From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

The extended region (safe range) is a region of guest physical
address space which is unused and could be safely used to create
grant/foreign mappings instead of wasting real RAM pages from
the domain memory for establishing these mappings.

The extended regions are chosen at the domain creation time and
advertised to it via "reg" property under hypervisor node in
the guest device-tree. As region 0 is reserved for grant table
space (always present), the indexes for extended regions are 1...N.
If extended regions could not be allocated for some reason,
Xen doesn't fail and behaves as usual, so only inserts region 0.

Please note the following limitations:
- The extended region feature is only supported for 64-bit domain
  currently.
- The ACPI case is not covered.

***

As Dom0 is direct mapped domain on Arm (e.g. MFN == GFN)
the algorithm to choose extended regions for it is different
in comparison with the algorithm for non-direct mapped DomU.
What is more, that extended regions should be chosen differently
whether IOMMU is enabled or not.

Provide RAM not assigned to Dom0 if IOMMU is disabled or memory
holes found in host device-tree if otherwise. Make sure that
extended regions are 2MB-aligned and located within maximum possible
addressable physical memory range. The minimum size of extended
region is 64MB. The maximum number of extended regions is 128,
which is an artificial limit to minimize code changes (we reuse
struct meminfo to describe extended regions, so there are an array
field for 128 elements).

It worth mentioning that unallocated memory solution (when the IOMMU
is disabled) will work safely until Dom0 is able to allocate memory
outside of the original range.

Also introduce command line option to be able to globally enable or
disable support for extended regions for Dom0 (enabled by default).

Suggested-by: Julien Grall <jgrall@amazon.com>
Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

---
Please note, we need to decide which approach to use in find_unallocated_memory(),
you can find details at:
https://lore.kernel.org/xen-devel/28503e09-44c3-f623-bb8d-8778bb94225f@gmail.com/

Changes RFC -> V2:
   - update patch description
   - drop uneeded "extended-region" DT property

Changes V2 -> V3:
   - update patch description
   - add comment for "size" calculation in add_ext_regions()
   - clarify "end" calculation in find_unallocated_memory() and
     find_memory_holes()
   - only pick up regions with size >= 64MB
   - allocate reg dynamically instead of keeping on the stack in
     make_hypervisor_node()
   - do not show warning for 32-bit domain
   - drop Linux specific limits EXT_REGION_*
   - also cover "ranges" property in find_memory_holes()
   - add command line arg to enable/disable extended region support
---
 docs/misc/xen-command-line.pandoc |   7 +
 xen/arch/arm/domain_build.c       | 280 +++++++++++++++++++++++++++++++++++++-
 2 files changed, 284 insertions(+), 3 deletions(-)

diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
index 177e656..3bb8eb7 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -1081,6 +1081,13 @@ hardware domain is architecture dependent.
 Note that specifying zero as domU value means zero, while for dom0 it means
 to use the default.
 
+### ext_regions (Arm)
+> `= <boolean>`
+
+> Default : `true`
+
+Flag to globally enable or disable support for extended regions for dom0.
+
 ### flask
 > `= permissive | enforcing | late | disabled`
 
diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index d233d63..81997d5 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -34,6 +34,10 @@
 static unsigned int __initdata opt_dom0_max_vcpus;
 integer_param("dom0_max_vcpus", opt_dom0_max_vcpus);
 
+/* If true, the extended regions support is enabled for dom0 */
+static bool __initdata opt_ext_regions = true;
+boolean_param("ext_regions", opt_ext_regions);
+
 static u64 __initdata dom0_mem;
 static bool __initdata dom0_mem_set;
 
@@ -886,6 +890,233 @@ static int __init make_memory_node(const struct domain *d,
     return res;
 }
 
+static int __init add_ext_regions(unsigned long s, unsigned long e, void *data)
+{
+    struct meminfo *ext_regions = data;
+    paddr_t start, size;
+
+    if ( ext_regions->nr_banks >= ARRAY_SIZE(ext_regions->bank) )
+        return 0;
+
+    /* Both start and size of the extended region should be 2MB aligned */
+    start = (s + SZ_2M - 1) & ~(SZ_2M - 1);
+    if ( start > e )
+        return 0;
+
+    /*
+     * e is actually "end-1" because it is called by rangeset functions
+     * which are inclusive of the last address.
+     */
+    e += 1;
+    size = (e - start) & ~(SZ_2M - 1);
+    if ( size < MB(64) )
+        return 0;
+
+    ext_regions->bank[ext_regions->nr_banks].start = start;
+    ext_regions->bank[ext_regions->nr_banks].size = size;
+    ext_regions->nr_banks++;
+
+    return 0;
+}
+
+static int __init find_unallocated_memory(const struct kernel_info *kinfo,
+                                          struct meminfo *ext_regions)
+{
+    const struct meminfo *assign_mem = &kinfo->mem;
+    struct rangeset *unalloc_mem;
+    paddr_t start, end;
+    unsigned int i;
+    int res;
+
+    dt_dprintk("Find unallocated memory for extended regions\n");
+
+    unalloc_mem = rangeset_new(NULL, NULL, 0);
+    if ( !unalloc_mem )
+        return -ENOMEM;
+
+    /* Start with all available RAM */
+    for ( i = 0; i < bootinfo.mem.nr_banks; i++ )
+    {
+        start = bootinfo.mem.bank[i].start;
+        end = bootinfo.mem.bank[i].start + bootinfo.mem.bank[i].size;
+        res = rangeset_add_range(unalloc_mem, start, end - 1);
+        if ( res )
+        {
+            printk(XENLOG_ERR "Failed to add: %#"PRIx64"->%#"PRIx64"\n",
+                   start, end);
+            goto out;
+        }
+    }
+
+    /* Remove RAM assigned to Dom0 */
+    for ( i = 0; i < assign_mem->nr_banks; i++ )
+    {
+        start = assign_mem->bank[i].start;
+        end = assign_mem->bank[i].start + assign_mem->bank[i].size;
+        res = rangeset_remove_range(unalloc_mem, start, end - 1);
+        if ( res )
+        {
+            printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
+                   start, end);
+            goto out;
+        }
+    }
+
+    /* Remove reserved-memory regions */
+    for ( i = 0; i < bootinfo.reserved_mem.nr_banks; i++ )
+    {
+        start = bootinfo.reserved_mem.bank[i].start;
+        end = bootinfo.reserved_mem.bank[i].start +
+            bootinfo.reserved_mem.bank[i].size;
+        res = rangeset_remove_range(unalloc_mem, start, end - 1);
+        if ( res )
+        {
+            printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
+                   start, end);
+            goto out;
+        }
+    }
+
+    /* Remove grant table region */
+    start = kinfo->gnttab_start;
+    end = kinfo->gnttab_start + kinfo->gnttab_size;
+    res = rangeset_remove_range(unalloc_mem, start, end - 1);
+    if ( res )
+    {
+        printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
+               start, end);
+        goto out;
+    }
+
+    start = 0;
+    end = (1ULL << p2m_ipa_bits) - 1;
+    res = rangeset_report_ranges(unalloc_mem, start, end,
+                                 add_ext_regions, ext_regions);
+    if ( res )
+        ext_regions->nr_banks = 0;
+    else if ( !ext_regions->nr_banks )
+        res = -ENOENT;
+
+out:
+    rangeset_destroy(unalloc_mem);
+
+    return res;
+}
+
+static int __init find_memory_holes(const struct kernel_info *kinfo,
+                                    struct meminfo *ext_regions)
+{
+    struct dt_device_node *np;
+    struct rangeset *mem_holes;
+    paddr_t start, end;
+    unsigned int i;
+    int res;
+
+    dt_dprintk("Find memory holes for extended regions\n");
+
+    mem_holes = rangeset_new(NULL, NULL, 0);
+    if ( !mem_holes )
+        return -ENOMEM;
+
+    /* Start with maximum possible addressable physical memory range */
+    start = 0;
+    end = (1ULL << p2m_ipa_bits) - 1;
+    res = rangeset_add_range(mem_holes, start, end);
+    if ( res )
+    {
+        printk(XENLOG_ERR "Failed to add: %#"PRIx64"->%#"PRIx64"\n",
+               start, end);
+        goto out;
+    }
+
+    /*
+     * Remove regions described by "reg" and "ranges" properties where
+     * the memory is addressable (MMIO, RAM, PCI BAR, etc).
+     */
+    dt_for_each_device_node( dt_host, np )
+    {
+        unsigned int naddr;
+        u64 addr, size;
+
+        naddr = dt_number_of_address(np);
+
+        for ( i = 0; i < naddr; i++ )
+        {
+            res = dt_device_get_address(np, i, &addr, &size);
+            if ( res )
+            {
+                printk(XENLOG_ERR "Unable to retrieve address %u for %s\n",
+                       i, dt_node_full_name(np));
+                goto out;
+            }
+
+            start = addr & PAGE_MASK;
+            end = PAGE_ALIGN(addr + size);
+            res = rangeset_remove_range(mem_holes, start, end - 1);
+            if ( res )
+            {
+                printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
+                       start, end);
+                goto out;
+            }
+        }
+
+        if ( dt_device_type_is_equal(np, "pci" ) )
+        {
+            unsigned int range_size, nr_ranges;
+            int na, ns, pna;
+            const __be32 *ranges;
+            u32 len;
+
+            /*
+             * Looking for non-empty ranges property which in the context
+             * of the PCI host bridge device node describes the BARs for
+             * the PCI devices.
+             */
+            ranges = dt_get_property(np, "ranges", &len);
+            if ( !ranges || !len )
+                continue;
+
+            pna = dt_n_addr_cells(np);
+            na = dt_child_n_addr_cells(np);
+            ns = dt_child_n_size_cells(np);
+            range_size = pna + na + ns;
+            nr_ranges = len / sizeof(__be32) / range_size;
+
+            for ( i = 0; i < nr_ranges; i++, ranges += range_size )
+            {
+                /* Skip the child address and get the parent (CPU) address */
+                addr = dt_read_number(ranges + na, pna);
+                size = dt_read_number(ranges + na + pna, ns);
+
+                start = addr & PAGE_MASK;
+                end = PAGE_ALIGN(addr + size);
+                res = rangeset_remove_range(mem_holes, start, end - 1);
+                if ( res )
+                {
+                    printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
+                           start, end);
+                    goto out;
+                }
+            }
+        }
+    }
+
+    start = 0;
+    end = (1ULL << p2m_ipa_bits) - 1;
+    res = rangeset_report_ranges(mem_holes, start, end,
+                                 add_ext_regions,  ext_regions);
+    if ( res )
+        ext_regions->nr_banks = 0;
+    else if ( !ext_regions->nr_banks )
+        res = -ENOENT;
+
+out:
+    rangeset_destroy(mem_holes);
+
+    return res;
+}
+
 static int __init make_hypervisor_node(struct domain *d,
                                        const struct kernel_info *kinfo,
                                        int addrcells, int sizecells)
@@ -893,11 +1124,12 @@ static int __init make_hypervisor_node(struct domain *d,
     const char compat[] =
         "xen,xen-"__stringify(XEN_VERSION)"."__stringify(XEN_SUBVERSION)"\0"
         "xen,xen";
-    __be32 reg[4];
+    __be32 *reg, *cells;
     gic_interrupt_t intr;
-    __be32 *cells;
     int res;
     void *fdt = kinfo->fdt;
+    struct meminfo *ext_regions;
+    unsigned int i;
 
     dt_dprintk("Create hypervisor node\n");
 
@@ -919,12 +1151,54 @@ static int __init make_hypervisor_node(struct domain *d,
     if ( res )
         return res;
 
+    reg = xzalloc_array(__be32, (NR_MEM_BANKS + 1) * 4);
+    if ( !reg )
+        return -ENOMEM;
+
+    ext_regions = xzalloc(struct meminfo);
+    if ( !ext_regions )
+    {
+        xfree(reg);
+        return -ENOMEM;
+    }
+
+    if ( !opt_ext_regions )
+        printk(XENLOG_DEBUG "The extended regions support is disabled\n");
+    else if ( is_32bit_domain(d) )
+        printk(XENLOG_DEBUG "The extended regions are only supported for 64-bit guest currently\n");
+    else
+    {
+        if ( !is_iommu_enabled(d) )
+            res = find_unallocated_memory(kinfo, ext_regions);
+        else
+            res = find_memory_holes(kinfo, ext_regions);
+
+        if ( res )
+            printk(XENLOG_WARNING "Failed to allocate extended regions\n");
+    }
+
     /* reg 0 is grant table space */
     cells = &reg[0];
     dt_child_set_range(&cells, addrcells, sizecells,
                        kinfo->gnttab_start, kinfo->gnttab_size);
+    /* reg 1...N are extended regions */
+    for ( i = 0; i < ext_regions->nr_banks; i++ )
+    {
+        u64 start = ext_regions->bank[i].start;
+        u64 size = ext_regions->bank[i].size;
+
+        dt_dprintk("Extended region %d: %#"PRIx64"->%#"PRIx64"\n",
+                   i, start, start + size);
+
+        dt_child_set_range(&cells, addrcells, sizecells, start, size);
+    }
+
     res = fdt_property(fdt, "reg", reg,
-                       dt_cells_to_size(addrcells + sizecells));
+                       dt_cells_to_size(addrcells + sizecells) *
+                       (ext_regions->nr_banks + 1));
+    xfree(ext_regions);
+    xfree(reg);
+
     if ( res )
         return res;
 
-- 
2.7.4

On Fri, 24 Sep 2021, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> 
> The extended region (safe range) is a region of guest physical
> address space which is unused and could be safely used to create
> grant/foreign mappings instead of wasting real RAM pages from
> the domain memory for establishing these mappings.
> 
> The extended regions are chosen at the domain creation time and
> advertised to it via "reg" property under hypervisor node in
> the guest device-tree. As region 0 is reserved for grant table
> space (always present), the indexes for extended regions are 1...N.
> If extended regions could not be allocated for some reason,
> Xen doesn't fail and behaves as usual, so only inserts region 0.
> 
> Please note the following limitations:
> - The extended region feature is only supported for 64-bit domain
>   currently.
> - The ACPI case is not covered.
> 
> ***
> 
> As Dom0 is direct mapped domain on Arm (e.g. MFN == GFN)
> the algorithm to choose extended regions for it is different
> in comparison with the algorithm for non-direct mapped DomU.
> What is more, that extended regions should be chosen differently
> whether IOMMU is enabled or not.
> 
> Provide RAM not assigned to Dom0 if IOMMU is disabled or memory
> holes found in host device-tree if otherwise. Make sure that
> extended regions are 2MB-aligned and located within maximum possible
> addressable physical memory range. The minimum size of extended
> region is 64MB. The maximum number of extended regions is 128,
> which is an artificial limit to minimize code changes (we reuse
> struct meminfo to describe extended regions, so there are an array
> field for 128 elements).
> 
> It worth mentioning that unallocated memory solution (when the IOMMU
> is disabled) will work safely until Dom0 is able to allocate memory
> outside of the original range.
> 
> Also introduce command line option to be able to globally enable or
> disable support for extended regions for Dom0 (enabled by default).
> 
> Suggested-by: Julien Grall <jgrall@amazon.com>
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> ---
> Please note, we need to decide which approach to use in find_unallocated_memory(),
> you can find details at:
> https://lore.kernel.org/xen-devel/28503e09-44c3-f623-bb8d-8778bb94225f@gmail.com/
> 
> Changes RFC -> V2:
>    - update patch description
>    - drop uneeded "extended-region" DT property
> 
> Changes V2 -> V3:
>    - update patch description
>    - add comment for "size" calculation in add_ext_regions()
>    - clarify "end" calculation in find_unallocated_memory() and
>      find_memory_holes()
>    - only pick up regions with size >= 64MB
>    - allocate reg dynamically instead of keeping on the stack in
>      make_hypervisor_node()
>    - do not show warning for 32-bit domain
>    - drop Linux specific limits EXT_REGION_*
>    - also cover "ranges" property in find_memory_holes()
>    - add command line arg to enable/disable extended region support
> ---
>  docs/misc/xen-command-line.pandoc |   7 +
>  xen/arch/arm/domain_build.c       | 280 +++++++++++++++++++++++++++++++++++++-
>  2 files changed, 284 insertions(+), 3 deletions(-)
> 
> diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
> index 177e656..3bb8eb7 100644
> --- a/docs/misc/xen-command-line.pandoc
> +++ b/docs/misc/xen-command-line.pandoc
> @@ -1081,6 +1081,13 @@ hardware domain is architecture dependent.
>  Note that specifying zero as domU value means zero, while for dom0 it means
>  to use the default.
>  
> +### ext_regions (Arm)
> +> `= <boolean>`
> +
> +> Default : `true`
> +
> +Flag to globally enable or disable support for extended regions for dom0.

I'd say:

Flag to enable or disable extended regions for Dom0.

Extended regions are ranges of unused address space exposed to Dom0 as
"safe to use" for special memory mappings. Disable if your board device
tree is incomplete.


>  ### flask
>  > `= permissive | enforcing | late | disabled`
>  
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index d233d63..81997d5 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -34,6 +34,10 @@
>  static unsigned int __initdata opt_dom0_max_vcpus;
>  integer_param("dom0_max_vcpus", opt_dom0_max_vcpus);
>  
> +/* If true, the extended regions support is enabled for dom0 */
> +static bool __initdata opt_ext_regions = true;
> +boolean_param("ext_regions", opt_ext_regions);
> +
>  static u64 __initdata dom0_mem;
>  static bool __initdata dom0_mem_set;
>  
> @@ -886,6 +890,233 @@ static int __init make_memory_node(const struct domain *d,
>      return res;
>  }
>  
> +static int __init add_ext_regions(unsigned long s, unsigned long e, void *data)
> +{
> +    struct meminfo *ext_regions = data;
> +    paddr_t start, size;
> +
> +    if ( ext_regions->nr_banks >= ARRAY_SIZE(ext_regions->bank) )
> +        return 0;
> +
> +    /* Both start and size of the extended region should be 2MB aligned */
> +    start = (s + SZ_2M - 1) & ~(SZ_2M - 1);
> +    if ( start > e )
> +        return 0;
> +
> +    /*
> +     * e is actually "end-1" because it is called by rangeset functions
> +     * which are inclusive of the last address.
> +     */
> +    e += 1;
> +    size = (e - start) & ~(SZ_2M - 1);
> +    if ( size < MB(64) )
> +        return 0;
> +
> +    ext_regions->bank[ext_regions->nr_banks].start = start;
> +    ext_regions->bank[ext_regions->nr_banks].size = size;
> +    ext_regions->nr_banks++;
> +
> +    return 0;
> +}

This is a lot better


> +static int __init find_unallocated_memory(const struct kernel_info *kinfo,
> +                                          struct meminfo *ext_regions)
> +{
> +    const struct meminfo *assign_mem = &kinfo->mem;
> +    struct rangeset *unalloc_mem;
> +    paddr_t start, end;
> +    unsigned int i;
> +    int res;
> +
> +    dt_dprintk("Find unallocated memory for extended regions\n");
> +
> +    unalloc_mem = rangeset_new(NULL, NULL, 0);
> +    if ( !unalloc_mem )
> +        return -ENOMEM;
> +
> +    /* Start with all available RAM */
> +    for ( i = 0; i < bootinfo.mem.nr_banks; i++ )
> +    {
> +        start = bootinfo.mem.bank[i].start;
> +        end = bootinfo.mem.bank[i].start + bootinfo.mem.bank[i].size;
> +        res = rangeset_add_range(unalloc_mem, start, end - 1);
> +        if ( res )
> +        {
> +            printk(XENLOG_ERR "Failed to add: %#"PRIx64"->%#"PRIx64"\n",
> +                   start, end);
> +            goto out;
> +        }
> +    }
> +
> +    /* Remove RAM assigned to Dom0 */
> +    for ( i = 0; i < assign_mem->nr_banks; i++ )
> +    {
> +        start = assign_mem->bank[i].start;
> +        end = assign_mem->bank[i].start + assign_mem->bank[i].size;
> +        res = rangeset_remove_range(unalloc_mem, start, end - 1);
> +        if ( res )
> +        {
> +            printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
> +                   start, end);
> +            goto out;
> +        }
> +    }
> +
> +    /* Remove reserved-memory regions */
> +    for ( i = 0; i < bootinfo.reserved_mem.nr_banks; i++ )
> +    {
> +        start = bootinfo.reserved_mem.bank[i].start;
> +        end = bootinfo.reserved_mem.bank[i].start +
> +            bootinfo.reserved_mem.bank[i].size;
> +        res = rangeset_remove_range(unalloc_mem, start, end - 1);
> +        if ( res )
> +        {
> +            printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
> +                   start, end);
> +            goto out;
> +        }
> +    }
> +
> +    /* Remove grant table region */
> +    start = kinfo->gnttab_start;
> +    end = kinfo->gnttab_start + kinfo->gnttab_size;
> +    res = rangeset_remove_range(unalloc_mem, start, end - 1);
> +    if ( res )
> +    {
> +        printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
> +               start, end);
> +        goto out;
> +    }
> +
> +    start = 0;
> +    end = (1ULL << p2m_ipa_bits) - 1;
> +    res = rangeset_report_ranges(unalloc_mem, start, end,
> +                                 add_ext_regions, ext_regions);
> +    if ( res )
> +        ext_regions->nr_banks = 0;
> +    else if ( !ext_regions->nr_banks )
> +        res = -ENOENT;
> +
> +out:
> +    rangeset_destroy(unalloc_mem);
> +
> +    return res;
> +}
> +
> +static int __init find_memory_holes(const struct kernel_info *kinfo,
> +                                    struct meminfo *ext_regions)
> +{
> +    struct dt_device_node *np;
> +    struct rangeset *mem_holes;
> +    paddr_t start, end;
> +    unsigned int i;
> +    int res;
> +
> +    dt_dprintk("Find memory holes for extended regions\n");
> +
> +    mem_holes = rangeset_new(NULL, NULL, 0);
> +    if ( !mem_holes )
> +        return -ENOMEM;
> +
> +    /* Start with maximum possible addressable physical memory range */
> +    start = 0;
> +    end = (1ULL << p2m_ipa_bits) - 1;
> +    res = rangeset_add_range(mem_holes, start, end);
> +    if ( res )
> +    {
> +        printk(XENLOG_ERR "Failed to add: %#"PRIx64"->%#"PRIx64"\n",
> +               start, end);
> +        goto out;
> +    }
> +
> +    /*
> +     * Remove regions described by "reg" and "ranges" properties where
> +     * the memory is addressable (MMIO, RAM, PCI BAR, etc).
> +     */
> +    dt_for_each_device_node( dt_host, np )
> +    {
> +        unsigned int naddr;
> +        u64 addr, size;
> +
> +        naddr = dt_number_of_address(np);
> +
> +        for ( i = 0; i < naddr; i++ )
> +        {
> +            res = dt_device_get_address(np, i, &addr, &size);
> +            if ( res )
> +            {
> +                printk(XENLOG_ERR "Unable to retrieve address %u for %s\n",
> +                       i, dt_node_full_name(np));
> +                goto out;
> +            }
> +
> +            start = addr & PAGE_MASK;

PAGE_ALIGN(addr)


> +            end = PAGE_ALIGN(addr + size);
> +            res = rangeset_remove_range(mem_holes, start, end - 1);
> +            if ( res )
> +            {
> +                printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
> +                       start, end);
> +                goto out;
> +            }
> +        }
> +
> +        if ( dt_device_type_is_equal(np, "pci" ) )
> +        {
> +            unsigned int range_size, nr_ranges;
> +            int na, ns, pna;
> +            const __be32 *ranges;
> +            u32 len;
> +
> +            /*
> +             * Looking for non-empty ranges property which in the context
> +             * of the PCI host bridge device node describes the BARs for
> +             * the PCI devices.

I'd say that "it describes the PCI host bridge aperture"


> +             */
> +            ranges = dt_get_property(np, "ranges", &len);
> +            if ( !ranges || !len )
> +                continue;
> +
> +            pna = dt_n_addr_cells(np);
> +            na = dt_child_n_addr_cells(np);
> +            ns = dt_child_n_size_cells(np);
> +
> +            range_size = pna + na + ns;
> +
> +            nr_ranges = len / sizeof(__be32) / range_size;
> +
> +            for ( i = 0; i < nr_ranges; i++, ranges += range_size )
> +            {
> +                /* Skip the child address and get the parent (CPU) address */
> +                addr = dt_read_number(ranges + na, pna);
> +
> +                size = dt_read_number(ranges + na + pna, ns);

Parsing the PCI ranges property is never intuitive, but everything
checks out as far as I can tell


> +                start = addr & PAGE_MASK;

PAGE_ALIGN(start)


> +                end = PAGE_ALIGN(addr + size);
> +                res = rangeset_remove_range(mem_holes, start, end - 1);
> +                if ( res )
> +                {
> +                    printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
> +                           start, end);
> +                    goto out;
> +                }
> +            }
> +        }
> +    }
> +
> +    start = 0;
> +    end = (1ULL << p2m_ipa_bits) - 1;
> +    res = rangeset_report_ranges(mem_holes, start, end,
> +                                 add_ext_regions,  ext_regions);
> +    if ( res )
> +        ext_regions->nr_banks = 0;
> +    else if ( !ext_regions->nr_banks )
> +        res = -ENOENT;
> +
> +out:
> +    rangeset_destroy(mem_holes);
> +
> +    return res;
> +}
> +
>  static int __init make_hypervisor_node(struct domain *d,
>                                         const struct kernel_info *kinfo,
>                                         int addrcells, int sizecells)
> @@ -893,11 +1124,12 @@ static int __init make_hypervisor_node(struct domain *d,
>      const char compat[] =
>          "xen,xen-"__stringify(XEN_VERSION)"."__stringify(XEN_SUBVERSION)"\0"
>          "xen,xen";
> -    __be32 reg[4];
> +    __be32 *reg, *cells;
>      gic_interrupt_t intr;
> -    __be32 *cells;
>      int res;
>      void *fdt = kinfo->fdt;
> +    struct meminfo *ext_regions;
> +    unsigned int i;
>  
>      dt_dprintk("Create hypervisor node\n");
>  
> @@ -919,12 +1151,54 @@ static int __init make_hypervisor_node(struct domain *d,
>      if ( res )
>          return res;
>  
> +    reg = xzalloc_array(__be32, (NR_MEM_BANKS + 1) * 4);
> +    if ( !reg )
> +        return -ENOMEM;

Instead of (NR_MEM_BANKS + 1) * 4, shouldn't it be:

(ext_regions->nr_banks + 1) * (addrcells + sizecells)

?

xzalloc_array allocates a number of elements, not a number of bytes.


> +
> +    ext_regions = xzalloc(struct meminfo);
> +    if ( !ext_regions )
> +    {
> +        xfree(reg);
> +        return -ENOMEM;
> +    }
> +
> +    if ( !opt_ext_regions )
> +        printk(XENLOG_DEBUG "The extended regions support is disabled\n");
> +    else if ( is_32bit_domain(d) )
> +        printk(XENLOG_DEBUG "The extended regions are only supported for 64-bit guest currently\n");

These checks should be before the memory allocations


> +    else
> +    {
> +        if ( !is_iommu_enabled(d) )
> +            res = find_unallocated_memory(kinfo, ext_regions);
> +        else
> +            res = find_memory_holes(kinfo, ext_regions);
> +
> +        if ( res )
> +            printk(XENLOG_WARNING "Failed to allocate extended regions\n");
> +    }
> +
>      /* reg 0 is grant table space */
>      cells = &reg[0];
>      dt_child_set_range(&cells, addrcells, sizecells,
>                         kinfo->gnttab_start, kinfo->gnttab_size);
> +    /* reg 1...N are extended regions */
> +    for ( i = 0; i < ext_regions->nr_banks; i++ )
> +    {
> +        u64 start = ext_regions->bank[i].start;
> +        u64 size = ext_regions->bank[i].size;
> +
> +        dt_dprintk("Extended region %d: %#"PRIx64"->%#"PRIx64"\n",
> +                   i, start, start + size);
> +
> +        dt_child_set_range(&cells, addrcells, sizecells, start, size);
> +    }
> +
>      res = fdt_property(fdt, "reg", reg,
> -                       dt_cells_to_size(addrcells + sizecells));
> +                       dt_cells_to_size(addrcells + sizecells) *
> +                       (ext_regions->nr_banks + 1));
> +    xfree(ext_regions);
> +    xfree(reg);
> +
>      if ( res )
>          return res;
>  
> -- 
> 2.7.4
> 

On 25.09.21 01:39, Stefano Stabellini wrote:

Hi Stefano

> On Fri, 24 Sep 2021, Oleksandr Tyshchenko wrote:
>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>
>> The extended region (safe range) is a region of guest physical
>> address space which is unused and could be safely used to create
>> grant/foreign mappings instead of wasting real RAM pages from
>> the domain memory for establishing these mappings.
>>
>> The extended regions are chosen at the domain creation time and
>> advertised to it via "reg" property under hypervisor node in
>> the guest device-tree. As region 0 is reserved for grant table
>> space (always present), the indexes for extended regions are 1...N.
>> If extended regions could not be allocated for some reason,
>> Xen doesn't fail and behaves as usual, so only inserts region 0.
>>
>> Please note the following limitations:
>> - The extended region feature is only supported for 64-bit domain
>>    currently.
>> - The ACPI case is not covered.
>>
>> ***
>>
>> As Dom0 is direct mapped domain on Arm (e.g. MFN == GFN)
>> the algorithm to choose extended regions for it is different
>> in comparison with the algorithm for non-direct mapped DomU.
>> What is more, that extended regions should be chosen differently
>> whether IOMMU is enabled or not.
>>
>> Provide RAM not assigned to Dom0 if IOMMU is disabled or memory
>> holes found in host device-tree if otherwise. Make sure that
>> extended regions are 2MB-aligned and located within maximum possible
>> addressable physical memory range. The minimum size of extended
>> region is 64MB. The maximum number of extended regions is 128,
>> which is an artificial limit to minimize code changes (we reuse
>> struct meminfo to describe extended regions, so there are an array
>> field for 128 elements).
>>
>> It worth mentioning that unallocated memory solution (when the IOMMU
>> is disabled) will work safely until Dom0 is able to allocate memory
>> outside of the original range.
>>
>> Also introduce command line option to be able to globally enable or
>> disable support for extended regions for Dom0 (enabled by default).
>>
>> Suggested-by: Julien Grall <jgrall@amazon.com>
>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>> ---
>> Please note, we need to decide which approach to use in find_unallocated_memory(),
>> you can find details at:
>> https://lore.kernel.org/xen-devel/28503e09-44c3-f623-bb8d-8778bb94225f@gmail.com/
>>
>> Changes RFC -> V2:
>>     - update patch description
>>     - drop uneeded "extended-region" DT property
>>
>> Changes V2 -> V3:
>>     - update patch description
>>     - add comment for "size" calculation in add_ext_regions()
>>     - clarify "end" calculation in find_unallocated_memory() and
>>       find_memory_holes()
>>     - only pick up regions with size >= 64MB
>>     - allocate reg dynamically instead of keeping on the stack in
>>       make_hypervisor_node()
>>     - do not show warning for 32-bit domain
>>     - drop Linux specific limits EXT_REGION_*
>>     - also cover "ranges" property in find_memory_holes()
>>     - add command line arg to enable/disable extended region support
>> ---
>>   docs/misc/xen-command-line.pandoc |   7 +
>>   xen/arch/arm/domain_build.c       | 280 +++++++++++++++++++++++++++++++++++++-
>>   2 files changed, 284 insertions(+), 3 deletions(-)
>>
>> diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
>> index 177e656..3bb8eb7 100644
>> --- a/docs/misc/xen-command-line.pandoc
>> +++ b/docs/misc/xen-command-line.pandoc
>> @@ -1081,6 +1081,13 @@ hardware domain is architecture dependent.
>>   Note that specifying zero as domU value means zero, while for dom0 it means
>>   to use the default.
>>   
>> +### ext_regions (Arm)
>> +> `= <boolean>`
>> +
>> +> Default : `true`
>> +
>> +Flag to globally enable or disable support for extended regions for dom0.
> I'd say:
>
> Flag to enable or disable extended regions for Dom0.
>
> Extended regions are ranges of unused address space exposed to Dom0 as
> "safe to use" for special memory mappings. Disable if your board device
> tree is incomplete.


ok, will update


>
>
>>   ### flask
>>   > `= permissive | enforcing | late | disabled`
>>   
>> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
>> index d233d63..81997d5 100644
>> --- a/xen/arch/arm/domain_build.c
>> +++ b/xen/arch/arm/domain_build.c
>> @@ -34,6 +34,10 @@
>>   static unsigned int __initdata opt_dom0_max_vcpus;
>>   integer_param("dom0_max_vcpus", opt_dom0_max_vcpus);
>>   
>> +/* If true, the extended regions support is enabled for dom0 */
>> +static bool __initdata opt_ext_regions = true;
>> +boolean_param("ext_regions", opt_ext_regions);
>> +
>>   static u64 __initdata dom0_mem;
>>   static bool __initdata dom0_mem_set;
>>   
>> @@ -886,6 +890,233 @@ static int __init make_memory_node(const struct domain *d,
>>       return res;
>>   }
>>   
>> +static int __init add_ext_regions(unsigned long s, unsigned long e, void *data)
>> +{
>> +    struct meminfo *ext_regions = data;
>> +    paddr_t start, size;
>> +
>> +    if ( ext_regions->nr_banks >= ARRAY_SIZE(ext_regions->bank) )
>> +        return 0;
>> +
>> +    /* Both start and size of the extended region should be 2MB aligned */
>> +    start = (s + SZ_2M - 1) & ~(SZ_2M - 1);
>> +    if ( start > e )
>> +        return 0;
>> +
>> +    /*
>> +     * e is actually "end-1" because it is called by rangeset functions
>> +     * which are inclusive of the last address.
>> +     */
>> +    e += 1;
>> +    size = (e - start) & ~(SZ_2M - 1);
>> +    if ( size < MB(64) )
>> +        return 0;
>> +
>> +    ext_regions->bank[ext_regions->nr_banks].start = start;
>> +    ext_regions->bank[ext_regions->nr_banks].size = size;
>> +    ext_regions->nr_banks++;
>> +
>> +    return 0;
>> +}
> This is a lot better

Great!


>
>
>> +static int __init find_unallocated_memory(const struct kernel_info *kinfo,
>> +                                          struct meminfo *ext_regions)
>> +{
>> +    const struct meminfo *assign_mem = &kinfo->mem;
>> +    struct rangeset *unalloc_mem;
>> +    paddr_t start, end;
>> +    unsigned int i;
>> +    int res;
>> +
>> +    dt_dprintk("Find unallocated memory for extended regions\n");
>> +
>> +    unalloc_mem = rangeset_new(NULL, NULL, 0);
>> +    if ( !unalloc_mem )
>> +        return -ENOMEM;
>> +
>> +    /* Start with all available RAM */
>> +    for ( i = 0; i < bootinfo.mem.nr_banks; i++ )
>> +    {
>> +        start = bootinfo.mem.bank[i].start;
>> +        end = bootinfo.mem.bank[i].start + bootinfo.mem.bank[i].size;
>> +        res = rangeset_add_range(unalloc_mem, start, end - 1);
>> +        if ( res )
>> +        {
>> +            printk(XENLOG_ERR "Failed to add: %#"PRIx64"->%#"PRIx64"\n",
>> +                   start, end);
>> +            goto out;
>> +        }
>> +    }
>> +
>> +    /* Remove RAM assigned to Dom0 */
>> +    for ( i = 0; i < assign_mem->nr_banks; i++ )
>> +    {
>> +        start = assign_mem->bank[i].start;
>> +        end = assign_mem->bank[i].start + assign_mem->bank[i].size;
>> +        res = rangeset_remove_range(unalloc_mem, start, end - 1);
>> +        if ( res )
>> +        {
>> +            printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
>> +                   start, end);
>> +            goto out;
>> +        }
>> +    }
>> +
>> +    /* Remove reserved-memory regions */
>> +    for ( i = 0; i < bootinfo.reserved_mem.nr_banks; i++ )
>> +    {
>> +        start = bootinfo.reserved_mem.bank[i].start;
>> +        end = bootinfo.reserved_mem.bank[i].start +
>> +            bootinfo.reserved_mem.bank[i].size;
>> +        res = rangeset_remove_range(unalloc_mem, start, end - 1);
>> +        if ( res )
>> +        {
>> +            printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
>> +                   start, end);
>> +            goto out;
>> +        }
>> +    }
>> +
>> +    /* Remove grant table region */
>> +    start = kinfo->gnttab_start;
>> +    end = kinfo->gnttab_start + kinfo->gnttab_size;
>> +    res = rangeset_remove_range(unalloc_mem, start, end - 1);
>> +    if ( res )
>> +    {
>> +        printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
>> +               start, end);
>> +        goto out;
>> +    }
>> +
>> +    start = 0;
>> +    end = (1ULL << p2m_ipa_bits) - 1;
>> +    res = rangeset_report_ranges(unalloc_mem, start, end,
>> +                                 add_ext_regions, ext_regions);
>> +    if ( res )
>> +        ext_regions->nr_banks = 0;
>> +    else if ( !ext_regions->nr_banks )
>> +        res = -ENOENT;
>> +
>> +out:
>> +    rangeset_destroy(unalloc_mem);
>> +
>> +    return res;
>> +}
>> +
>> +static int __init find_memory_holes(const struct kernel_info *kinfo,
>> +                                    struct meminfo *ext_regions)
>> +{
>> +    struct dt_device_node *np;
>> +    struct rangeset *mem_holes;
>> +    paddr_t start, end;
>> +    unsigned int i;
>> +    int res;
>> +
>> +    dt_dprintk("Find memory holes for extended regions\n");
>> +
>> +    mem_holes = rangeset_new(NULL, NULL, 0);
>> +    if ( !mem_holes )
>> +        return -ENOMEM;
>> +
>> +    /* Start with maximum possible addressable physical memory range */
>> +    start = 0;
>> +    end = (1ULL << p2m_ipa_bits) - 1;
>> +    res = rangeset_add_range(mem_holes, start, end);
>> +    if ( res )
>> +    {
>> +        printk(XENLOG_ERR "Failed to add: %#"PRIx64"->%#"PRIx64"\n",
>> +               start, end);
>> +        goto out;
>> +    }
>> +
>> +    /*
>> +     * Remove regions described by "reg" and "ranges" properties where
>> +     * the memory is addressable (MMIO, RAM, PCI BAR, etc).
>> +     */
>> +    dt_for_each_device_node( dt_host, np )
>> +    {
>> +        unsigned int naddr;
>> +        u64 addr, size;
>> +
>> +        naddr = dt_number_of_address(np);
>> +
>> +        for ( i = 0; i < naddr; i++ )
>> +        {
>> +            res = dt_device_get_address(np, i, &addr, &size);
>> +            if ( res )
>> +            {
>> +                printk(XENLOG_ERR "Unable to retrieve address %u for %s\n",
>> +                       i, dt_node_full_name(np));
>> +                goto out;
>> +            }
>> +
>> +            start = addr & PAGE_MASK;
> PAGE_ALIGN(addr)

Let's imagine we have reg = <0x0 0xee080200 0x0 0x700>;
So using PAGE_ALIGN(0xee080200) we will get a result aligned up - 
0xee081000, but this is not what we want here. But, the end should be 
aligned up.


>
>
>> +            end = PAGE_ALIGN(addr + size);
>> +            res = rangeset_remove_range(mem_holes, start, end - 1);
>> +            if ( res )
>> +            {
>> +                printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
>> +                       start, end);
>> +                goto out;
>> +            }
>> +        }
>> +
>> +        if ( dt_device_type_is_equal(np, "pci" ) )
>> +        {
>> +            unsigned int range_size, nr_ranges;
>> +            int na, ns, pna;
>> +            const __be32 *ranges;
>> +            u32 len;
>> +
>> +            /*
>> +             * Looking for non-empty ranges property which in the context
>> +             * of the PCI host bridge device node describes the BARs for
>> +             * the PCI devices.
> I'd say that "it describes the PCI host bridge aperture"

ok, will update


>
>
>> +             */
>> +            ranges = dt_get_property(np, "ranges", &len);
>> +            if ( !ranges || !len )
>> +                continue;
>> +
>> +            pna = dt_n_addr_cells(np);
>> +            na = dt_child_n_addr_cells(np);
>> +            ns = dt_child_n_size_cells(np);
>> +
>> +            range_size = pna + na + ns;
>> +
>> +            nr_ranges = len / sizeof(__be32) / range_size;
>> +
>> +            for ( i = 0; i < nr_ranges; i++, ranges += range_size )
>> +            {
>> +                /* Skip the child address and get the parent (CPU) address */
>> +                addr = dt_read_number(ranges + na, pna);
>> +
>> +                size = dt_read_number(ranges + na + pna, ns);
> Parsing the PCI ranges property is never intuitive, but everything
> checks out as far as I can tell
>
>
>> +                start = addr & PAGE_MASK;
> PAGE_ALIGN(start)

same here


>
>
>> +                end = PAGE_ALIGN(addr + size);
>> +                res = rangeset_remove_range(mem_holes, start, end - 1);
>> +                if ( res )
>> +                {
>> +                    printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
>> +                           start, end);
>> +                    goto out;
>> +                }
>> +            }
>> +        }
>> +    }
>> +
>> +    start = 0;
>> +    end = (1ULL << p2m_ipa_bits) - 1;
>> +    res = rangeset_report_ranges(mem_holes, start, end,
>> +                                 add_ext_regions,  ext_regions);
>> +    if ( res )
>> +        ext_regions->nr_banks = 0;
>> +    else if ( !ext_regions->nr_banks )
>> +        res = -ENOENT;
>> +
>> +out:
>> +    rangeset_destroy(mem_holes);
>> +
>> +    return res;
>> +}
>> +
>>   static int __init make_hypervisor_node(struct domain *d,
>>                                          const struct kernel_info *kinfo,
>>                                          int addrcells, int sizecells)
>> @@ -893,11 +1124,12 @@ static int __init make_hypervisor_node(struct domain *d,
>>       const char compat[] =
>>           "xen,xen-"__stringify(XEN_VERSION)"."__stringify(XEN_SUBVERSION)"\0"
>>           "xen,xen";
>> -    __be32 reg[4];
>> +    __be32 *reg, *cells;
>>       gic_interrupt_t intr;
>> -    __be32 *cells;
>>       int res;
>>       void *fdt = kinfo->fdt;
>> +    struct meminfo *ext_regions;
>> +    unsigned int i;
>>   
>>       dt_dprintk("Create hypervisor node\n");
>>   
>> @@ -919,12 +1151,54 @@ static int __init make_hypervisor_node(struct domain *d,
>>       if ( res )
>>           return res;
>>   
>> +    reg = xzalloc_array(__be32, (NR_MEM_BANKS + 1) * 4);
>> +    if ( !reg )
>> +        return -ENOMEM;
> Instead of (NR_MEM_BANKS + 1) * 4, shouldn't it be:
>
> (ext_regions->nr_banks + 1) * (addrcells + sizecells)
>
> ?

I think, yes ... But, with other modifications. Please see below


>
> xzalloc_array allocates a number of elements, not a number of bytes.
>
>
>> +
>> +    ext_regions = xzalloc(struct meminfo);
>> +    if ( !ext_regions )
>> +    {
>> +        xfree(reg);
>> +        return -ENOMEM;
>> +    }
>> +
>> +    if ( !opt_ext_regions )
>> +        printk(XENLOG_DEBUG "The extended regions support is disabled\n");
>> +    else if ( is_32bit_domain(d) )
>> +        printk(XENLOG_DEBUG "The extended regions are only supported for 64-bit guest currently\n");
> These checks should be before the memory allocations

Good point! Indeed there is no sense of whole "ext_regions" allocations 
if we are not going to handle extended regions. Also there is no need
to allocate "reg" array with maximum possible elements in advance 
(NR_MEM_BANKS + 1) * 4, we can allocate it afterwards when we clearly 
know how many elements we really need
(nr_ext_regions + 1) * 4, as you suggested above.


Below the changes to this function on top of current patch:

@@ -1128,8 +1127,8 @@ static int __init make_hypervisor_node(struct 
domain *d,
      gic_interrupt_t intr;
      int res;
      void *fdt = kinfo->fdt;
-    struct meminfo *ext_regions;
-    unsigned int i;
+    struct meminfo *ext_regions = NULL;
+    unsigned int i, nr_ext_regions;

      dt_dprintk("Create hypervisor node\n");

@@ -1151,23 +1150,22 @@ static int __init make_hypervisor_node(struct 
domain *d,
      if ( res )
          return res;

-    reg = xzalloc_array(__be32, (NR_MEM_BANKS + 1) * 4);
-    if ( !reg )
-        return -ENOMEM;
-
-    ext_regions = xzalloc(struct meminfo);
-    if ( !ext_regions )
-    {
-        xfree(reg);
-        return -ENOMEM;
-    }
-
      if ( !opt_ext_regions )
+    {
          printk(XENLOG_DEBUG "The extended regions support is disabled\n");
+        nr_ext_regions = 0;
+    }
      else if ( is_32bit_domain(d) )
+    {
          printk(XENLOG_DEBUG "The extended regions are only supported 
for 64-bit guest currently\n");
+        nr_ext_regions = 0;
+    }
      else
      {
+        ext_regions = xzalloc(struct meminfo);
+        if ( !ext_regions )
+            return -ENOMEM;
+
          if ( !is_iommu_enabled(d) )
              res = find_unallocated_memory(kinfo, ext_regions);
          else
@@ -1175,6 +1173,14 @@ static int __init make_hypervisor_node(struct 
domain *d,

          if ( res )
              printk(XENLOG_WARNING "Failed to allocate extended 
regions\n");
+        nr_ext_regions = ext_regions->nr_banks;
+    }
+
+    reg = xzalloc_array(__be32, (nr_ext_regions + 1) * (addrcells + 
sizecells));
+    if ( !reg )
+    {
+        xfree(ext_regions);
+        return -ENOMEM;
      }

      /* reg 0 is grant table space */
@@ -1182,7 +1188,7 @@ static int __init make_hypervisor_node(struct 
domain *d,
      dt_child_set_range(&cells, addrcells, sizecells,
                         kinfo->gnttab_start, kinfo->gnttab_size);
      /* reg 1...N are extended regions */
-    for ( i = 0; i < ext_regions->nr_banks; i++ )
+    for ( i = 0; i < nr_ext_regions; i++ )
      {
          u64 start = ext_regions->bank[i].start;
          u64 size = ext_regions->bank[i].size;
@@ -1195,7 +1201,7 @@ static int __init make_hypervisor_node(struct 
domain *d,

      res = fdt_property(fdt, "reg", reg,
                         dt_cells_to_size(addrcells + sizecells) *
-                       (ext_regions->nr_banks + 1));
+                       (nr_ext_regions + 1));
      xfree(ext_regions);
      xfree(reg);

(END)



>
>
>> +    else
>> +    {
>> +        if ( !is_iommu_enabled(d) )
>> +            res = find_unallocated_memory(kinfo, ext_regions);
>> +        else
>> +            res = find_memory_holes(kinfo, ext_regions);
>> +
>> +        if ( res )
>> +            printk(XENLOG_WARNING "Failed to allocate extended regions\n");
>> +    }
>> +
>>       /* reg 0 is grant table space */
>>       cells = &reg[0];
>>       dt_child_set_range(&cells, addrcells, sizecells,
>>                          kinfo->gnttab_start, kinfo->gnttab_size);
>> +    /* reg 1...N are extended regions */
>> +    for ( i = 0; i < ext_regions->nr_banks; i++ )
>> +    {
>> +        u64 start = ext_regions->bank[i].start;
>> +        u64 size = ext_regions->bank[i].size;
>> +
>> +        dt_dprintk("Extended region %d: %#"PRIx64"->%#"PRIx64"\n",
>> +                   i, start, start + size);
>> +
>> +        dt_child_set_range(&cells, addrcells, sizecells, start, size);
>> +    }
>> +
>>       res = fdt_property(fdt, "reg", reg,
>> -                       dt_cells_to_size(addrcells + sizecells));
>> +                       dt_cells_to_size(addrcells + sizecells) *
>> +                       (ext_regions->nr_banks + 1));
>> +    xfree(ext_regions);
>> +    xfree(reg);
>> +
>>       if ( res )
>>           return res;
>>   
>> -- 
>> 2.7.4
>>
-- 
Regards,

Oleksandr Tyshchenko

On Sat, 25 Sep 2021, Oleksandr wrote:
> On 25.09.21 01:39, Stefano Stabellini wrote:
> > On Fri, 24 Sep 2021, Oleksandr Tyshchenko wrote:
> > > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> > > 
> > > The extended region (safe range) is a region of guest physical
> > > address space which is unused and could be safely used to create
> > > grant/foreign mappings instead of wasting real RAM pages from
> > > the domain memory for establishing these mappings.
> > > 
> > > The extended regions are chosen at the domain creation time and
> > > advertised to it via "reg" property under hypervisor node in
> > > the guest device-tree. As region 0 is reserved for grant table
> > > space (always present), the indexes for extended regions are 1...N.
> > > If extended regions could not be allocated for some reason,
> > > Xen doesn't fail and behaves as usual, so only inserts region 0.
> > > 
> > > Please note the following limitations:
> > > - The extended region feature is only supported for 64-bit domain
> > >    currently.
> > > - The ACPI case is not covered.
> > > 
> > > ***
> > > 
> > > As Dom0 is direct mapped domain on Arm (e.g. MFN == GFN)
> > > the algorithm to choose extended regions for it is different
> > > in comparison with the algorithm for non-direct mapped DomU.
> > > What is more, that extended regions should be chosen differently
> > > whether IOMMU is enabled or not.
> > > 
> > > Provide RAM not assigned to Dom0 if IOMMU is disabled or memory
> > > holes found in host device-tree if otherwise. Make sure that
> > > extended regions are 2MB-aligned and located within maximum possible
> > > addressable physical memory range. The minimum size of extended
> > > region is 64MB. The maximum number of extended regions is 128,
> > > which is an artificial limit to minimize code changes (we reuse
> > > struct meminfo to describe extended regions, so there are an array
> > > field for 128 elements).
> > > 
> > > It worth mentioning that unallocated memory solution (when the IOMMU
> > > is disabled) will work safely until Dom0 is able to allocate memory
> > > outside of the original range.
> > > 
> > > Also introduce command line option to be able to globally enable or
> > > disable support for extended regions for Dom0 (enabled by default).
> > > 
> > > Suggested-by: Julien Grall <jgrall@amazon.com>
> > > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> > > ---
> > > Please note, we need to decide which approach to use in
> > > find_unallocated_memory(),
> > > you can find details at:
> > > https://lore.kernel.org/xen-devel/28503e09-44c3-f623-bb8d-8778bb94225f@gmail.com/
> > > 
> > > Changes RFC -> V2:
> > >     - update patch description
> > >     - drop uneeded "extended-region" DT property
> > > 
> > > Changes V2 -> V3:
> > >     - update patch description
> > >     - add comment for "size" calculation in add_ext_regions()
> > >     - clarify "end" calculation in find_unallocated_memory() and
> > >       find_memory_holes()
> > >     - only pick up regions with size >= 64MB
> > >     - allocate reg dynamically instead of keeping on the stack in
> > >       make_hypervisor_node()
> > >     - do not show warning for 32-bit domain
> > >     - drop Linux specific limits EXT_REGION_*
> > >     - also cover "ranges" property in find_memory_holes()
> > >     - add command line arg to enable/disable extended region support
> > > ---
> > >   docs/misc/xen-command-line.pandoc |   7 +
> > >   xen/arch/arm/domain_build.c       | 280
> > > +++++++++++++++++++++++++++++++++++++-
> > >   2 files changed, 284 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/docs/misc/xen-command-line.pandoc
> > > b/docs/misc/xen-command-line.pandoc
> > > index 177e656..3bb8eb7 100644
> > > --- a/docs/misc/xen-command-line.pandoc
> > > +++ b/docs/misc/xen-command-line.pandoc
> > > @@ -1081,6 +1081,13 @@ hardware domain is architecture dependent.
> > >   Note that specifying zero as domU value means zero, while for dom0 it
> > > means
> > >   to use the default.
> > >   +### ext_regions (Arm)
> > > +> `= <boolean>`
> > > +
> > > +> Default : `true`
> > > +
> > > +Flag to globally enable or disable support for extended regions for dom0.
> > I'd say:
> > 
> > Flag to enable or disable extended regions for Dom0.
> > 
> > Extended regions are ranges of unused address space exposed to Dom0 as
> > "safe to use" for special memory mappings. Disable if your board device
> > tree is incomplete.
> 
> 
> ok, will update
> 
> 
> > 
> > 
> > >   ### flask
> > >   > `= permissive | enforcing | late | disabled`
> > >   diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> > > index d233d63..81997d5 100644
> > > --- a/xen/arch/arm/domain_build.c
> > > +++ b/xen/arch/arm/domain_build.c
> > > @@ -34,6 +34,10 @@
> > >   static unsigned int __initdata opt_dom0_max_vcpus;
> > >   integer_param("dom0_max_vcpus", opt_dom0_max_vcpus);
> > >   +/* If true, the extended regions support is enabled for dom0 */
> > > +static bool __initdata opt_ext_regions = true;
> > > +boolean_param("ext_regions", opt_ext_regions);
> > > +
> > >   static u64 __initdata dom0_mem;
> > >   static bool __initdata dom0_mem_set;
> > >   @@ -886,6 +890,233 @@ static int __init make_memory_node(const struct
> > > domain *d,
> > >       return res;
> > >   }
> > >   +static int __init add_ext_regions(unsigned long s, unsigned long e,
> > > void *data)
> > > +{
> > > +    struct meminfo *ext_regions = data;
> > > +    paddr_t start, size;
> > > +
> > > +    if ( ext_regions->nr_banks >= ARRAY_SIZE(ext_regions->bank) )
> > > +        return 0;
> > > +
> > > +    /* Both start and size of the extended region should be 2MB aligned
> > > */
> > > +    start = (s + SZ_2M - 1) & ~(SZ_2M - 1);
> > > +    if ( start > e )
> > > +        return 0;
> > > +
> > > +    /*
> > > +     * e is actually "end-1" because it is called by rangeset functions
> > > +     * which are inclusive of the last address.
> > > +     */
> > > +    e += 1;
> > > +    size = (e - start) & ~(SZ_2M - 1);
> > > +    if ( size < MB(64) )
> > > +        return 0;
> > > +
> > > +    ext_regions->bank[ext_regions->nr_banks].start = start;
> > > +    ext_regions->bank[ext_regions->nr_banks].size = size;
> > > +    ext_regions->nr_banks++;
> > > +
> > > +    return 0;
> > > +}
> > This is a lot better
> 
> Great!
> 
> 
> > 
> > 
> > > +static int __init find_unallocated_memory(const struct kernel_info
> > > *kinfo,
> > > +                                          struct meminfo *ext_regions)
> > > +{
> > > +    const struct meminfo *assign_mem = &kinfo->mem;
> > > +    struct rangeset *unalloc_mem;
> > > +    paddr_t start, end;
> > > +    unsigned int i;
> > > +    int res;
> > > +
> > > +    dt_dprintk("Find unallocated memory for extended regions\n");
> > > +
> > > +    unalloc_mem = rangeset_new(NULL, NULL, 0);
> > > +    if ( !unalloc_mem )
> > > +        return -ENOMEM;
> > > +
> > > +    /* Start with all available RAM */
> > > +    for ( i = 0; i < bootinfo.mem.nr_banks; i++ )
> > > +    {
> > > +        start = bootinfo.mem.bank[i].start;
> > > +        end = bootinfo.mem.bank[i].start + bootinfo.mem.bank[i].size;
> > > +        res = rangeset_add_range(unalloc_mem, start, end - 1);
> > > +        if ( res )
> > > +        {
> > > +            printk(XENLOG_ERR "Failed to add: %#"PRIx64"->%#"PRIx64"\n",
> > > +                   start, end);
> > > +            goto out;
> > > +        }
> > > +    }
> > > +
> > > +    /* Remove RAM assigned to Dom0 */
> > > +    for ( i = 0; i < assign_mem->nr_banks; i++ )
> > > +    {
> > > +        start = assign_mem->bank[i].start;
> > > +        end = assign_mem->bank[i].start + assign_mem->bank[i].size;
> > > +        res = rangeset_remove_range(unalloc_mem, start, end - 1);
> > > +        if ( res )
> > > +        {
> > > +            printk(XENLOG_ERR "Failed to remove:
> > > %#"PRIx64"->%#"PRIx64"\n",
> > > +                   start, end);
> > > +            goto out;
> > > +        }
> > > +    }
> > > +
> > > +    /* Remove reserved-memory regions */
> > > +    for ( i = 0; i < bootinfo.reserved_mem.nr_banks; i++ )
> > > +    {
> > > +        start = bootinfo.reserved_mem.bank[i].start;
> > > +        end = bootinfo.reserved_mem.bank[i].start +
> > > +            bootinfo.reserved_mem.bank[i].size;
> > > +        res = rangeset_remove_range(unalloc_mem, start, end - 1);
> > > +        if ( res )
> > > +        {
> > > +            printk(XENLOG_ERR "Failed to remove:
> > > %#"PRIx64"->%#"PRIx64"\n",
> > > +                   start, end);
> > > +            goto out;
> > > +        }
> > > +    }
> > > +
> > > +    /* Remove grant table region */
> > > +    start = kinfo->gnttab_start;
> > > +    end = kinfo->gnttab_start + kinfo->gnttab_size;
> > > +    res = rangeset_remove_range(unalloc_mem, start, end - 1);
> > > +    if ( res )
> > > +    {
> > > +        printk(XENLOG_ERR "Failed to remove: %#"PRIx64"->%#"PRIx64"\n",
> > > +               start, end);
> > > +        goto out;
> > > +    }
> > > +
> > > +    start = 0;
> > > +    end = (1ULL << p2m_ipa_bits) - 1;
> > > +    res = rangeset_report_ranges(unalloc_mem, start, end,
> > > +                                 add_ext_regions, ext_regions);
> > > +    if ( res )
> > > +        ext_regions->nr_banks = 0;
> > > +    else if ( !ext_regions->nr_banks )
> > > +        res = -ENOENT;
> > > +
> > > +out:
> > > +    rangeset_destroy(unalloc_mem);
> > > +
> > > +    return res;
> > > +}
> > > +
> > > +static int __init find_memory_holes(const struct kernel_info *kinfo,
> > > +                                    struct meminfo *ext_regions)
> > > +{
> > > +    struct dt_device_node *np;
> > > +    struct rangeset *mem_holes;
> > > +    paddr_t start, end;
> > > +    unsigned int i;
> > > +    int res;
> > > +
> > > +    dt_dprintk("Find memory holes for extended regions\n");
> > > +
> > > +    mem_holes = rangeset_new(NULL, NULL, 0);
> > > +    if ( !mem_holes )
> > > +        return -ENOMEM;
> > > +
> > > +    /* Start with maximum possible addressable physical memory range */
> > > +    start = 0;
> > > +    end = (1ULL << p2m_ipa_bits) - 1;
> > > +    res = rangeset_add_range(mem_holes, start, end);
> > > +    if ( res )
> > > +    {
> > > +        printk(XENLOG_ERR "Failed to add: %#"PRIx64"->%#"PRIx64"\n",
> > > +               start, end);
> > > +        goto out;
> > > +    }
> > > +
> > > +    /*
> > > +     * Remove regions described by "reg" and "ranges" properties where
> > > +     * the memory is addressable (MMIO, RAM, PCI BAR, etc).
> > > +     */
> > > +    dt_for_each_device_node( dt_host, np )
> > > +    {
> > > +        unsigned int naddr;
> > > +        u64 addr, size;
> > > +
> > > +        naddr = dt_number_of_address(np);
> > > +
> > > +        for ( i = 0; i < naddr; i++ )
> > > +        {
> > > +            res = dt_device_get_address(np, i, &addr, &size);
> > > +            if ( res )
> > > +            {
> > > +                printk(XENLOG_ERR "Unable to retrieve address %u for
> > > %s\n",
> > > +                       i, dt_node_full_name(np));
> > > +                goto out;
> > > +            }
> > > +
> > > +            start = addr & PAGE_MASK;
> > PAGE_ALIGN(addr)
> 
> Let's imagine we have reg = <0x0 0xee080200 0x0 0x700>;
> So using PAGE_ALIGN(0xee080200) we will get a result aligned up - 0xee081000,
> but this is not what we want here. But, the end should be aligned up.

You are right, we want to be conservative here, So PAGE_ALIGN is fine
for end, but for start we need "& PAGE_MASK".


 
> > > +            end = PAGE_ALIGN(addr + size);
> > > +            res = rangeset_remove_range(mem_holes, start, end - 1);
> > > +            if ( res )
> > > +            {
> > > +                printk(XENLOG_ERR "Failed to remove:
> > > %#"PRIx64"->%#"PRIx64"\n",
> > > +                       start, end);
> > > +                goto out;
> > > +            }
> > > +        }
> > > +
> > > +        if ( dt_device_type_is_equal(np, "pci" ) )
> > > +        {
> > > +            unsigned int range_size, nr_ranges;
> > > +            int na, ns, pna;
> > > +            const __be32 *ranges;
> > > +            u32 len;
> > > +
> > > +            /*
> > > +             * Looking for non-empty ranges property which in the context
> > > +             * of the PCI host bridge device node describes the BARs for
> > > +             * the PCI devices.
> > I'd say that "it describes the PCI host bridge aperture"
> 
> ok, will update
> 
> 
> > 
> > 
> > > +             */
> > > +            ranges = dt_get_property(np, "ranges", &len);
> > > +            if ( !ranges || !len )
> > > +                continue;
> > > +
> > > +            pna = dt_n_addr_cells(np);
> > > +            na = dt_child_n_addr_cells(np);
> > > +            ns = dt_child_n_size_cells(np);
> > > +
> > > +            range_size = pna + na + ns;
> > > +
> > > +            nr_ranges = len / sizeof(__be32) / range_size;
> > > +
> > > +            for ( i = 0; i < nr_ranges; i++, ranges += range_size )
> > > +            {
> > > +                /* Skip the child address and get the parent (CPU)
> > > address */
> > > +                addr = dt_read_number(ranges + na, pna);
> > > +
> > > +                size = dt_read_number(ranges + na + pna, ns);
> > Parsing the PCI ranges property is never intuitive, but everything
> > checks out as far as I can tell
> > 
> > 
> > > +                start = addr & PAGE_MASK;
> > PAGE_ALIGN(start)
> 
> same here
> 
> 
> > 
> > 
> > > +                end = PAGE_ALIGN(addr + size);
> > > +                res = rangeset_remove_range(mem_holes, start, end - 1);
> > > +                if ( res )
> > > +                {
> > > +                    printk(XENLOG_ERR "Failed to remove:
> > > %#"PRIx64"->%#"PRIx64"\n",
> > > +                           start, end);
> > > +                    goto out;
> > > +                }
> > > +            }
> > > +        }
> > > +    }
> > > +
> > > +    start = 0;
> > > +    end = (1ULL << p2m_ipa_bits) - 1;
> > > +    res = rangeset_report_ranges(mem_holes, start, end,
> > > +                                 add_ext_regions,  ext_regions);
> > > +    if ( res )
> > > +        ext_regions->nr_banks = 0;
> > > +    else if ( !ext_regions->nr_banks )
> > > +        res = -ENOENT;
> > > +
> > > +out:
> > > +    rangeset_destroy(mem_holes);
> > > +
> > > +    return res;
> > > +}
> > > +
> > >   static int __init make_hypervisor_node(struct domain *d,
> > >                                          const struct kernel_info *kinfo,
> > >                                          int addrcells, int sizecells)
> > > @@ -893,11 +1124,12 @@ static int __init make_hypervisor_node(struct
> > > domain *d,
> > >       const char compat[] =
> > >           "xen,xen-"__stringify(XEN_VERSION)"."__stringify(XEN_SUBVERSION)"\0"
> > >           "xen,xen";
> > > -    __be32 reg[4];
> > > +    __be32 *reg, *cells;
> > >       gic_interrupt_t intr;
> > > -    __be32 *cells;
> > >       int res;
> > >       void *fdt = kinfo->fdt;
> > > +    struct meminfo *ext_regions;
> > > +    unsigned int i;
> > >         dt_dprintk("Create hypervisor node\n");
> > >   @@ -919,12 +1151,54 @@ static int __init make_hypervisor_node(struct
> > > domain *d,
> > >       if ( res )
> > >           return res;
> > >   +    reg = xzalloc_array(__be32, (NR_MEM_BANKS + 1) * 4);
> > > +    if ( !reg )
> > > +        return -ENOMEM;
> > Instead of (NR_MEM_BANKS + 1) * 4, shouldn't it be:
> > 
> > (ext_regions->nr_banks + 1) * (addrcells + sizecells)
> > 
> > ?
> 
> I think, yes ... But, with other modifications. Please see below
> 
> 
> > 
> > xzalloc_array allocates a number of elements, not a number of bytes.
> > 
> > 
> > > +
> > > +    ext_regions = xzalloc(struct meminfo);
> > > +    if ( !ext_regions )
> > > +    {
> > > +        xfree(reg);
> > > +        return -ENOMEM;
> > > +    }
> > > +
> > > +    if ( !opt_ext_regions )
> > > +        printk(XENLOG_DEBUG "The extended regions support is
> > > disabled\n");
> > > +    else if ( is_32bit_domain(d) )
> > > +        printk(XENLOG_DEBUG "The extended regions are only supported for
> > > 64-bit guest currently\n");
> > These checks should be before the memory allocations
> 
> Good point! Indeed there is no sense of whole "ext_regions" allocations if we
> are not going to handle extended regions. Also there is no need
> to allocate "reg" array with maximum possible elements in advance
> (NR_MEM_BANKS + 1) * 4, we can allocate it afterwards when we clearly know how
> many elements we really need
> (nr_ext_regions + 1) * 4, as you suggested above.
> 
> 
> Below the changes to this function on top of current patch:
> 
> @@ -1128,8 +1127,8 @@ static int __init make_hypervisor_node(struct domain *d,
>      gic_interrupt_t intr;
>      int res;
>      void *fdt = kinfo->fdt;
> -    struct meminfo *ext_regions;
> -    unsigned int i;
> +    struct meminfo *ext_regions = NULL;
> +    unsigned int i, nr_ext_regions;
> 
>      dt_dprintk("Create hypervisor node\n");
> 
> @@ -1151,23 +1150,22 @@ static int __init make_hypervisor_node(struct domain
> *d,
>      if ( res )
>          return res;
> 
> -    reg = xzalloc_array(__be32, (NR_MEM_BANKS + 1) * 4);
> -    if ( !reg )
> -        return -ENOMEM;
> -
> -    ext_regions = xzalloc(struct meminfo);
> -    if ( !ext_regions )
> -    {
> -        xfree(reg);
> -        return -ENOMEM;
> -    }
> -
>      if ( !opt_ext_regions )
> +    {
>          printk(XENLOG_DEBUG "The extended regions support is disabled\n");
> +        nr_ext_regions = 0;
> +    }
>      else if ( is_32bit_domain(d) )
> +    {
>          printk(XENLOG_DEBUG "The extended regions are only supported for
> 64-bit guest currently\n");
> +        nr_ext_regions = 0;
> +    }
>      else
>      {
> +        ext_regions = xzalloc(struct meminfo);
> +        if ( !ext_regions )
> +            return -ENOMEM;
> +
>          if ( !is_iommu_enabled(d) )
>              res = find_unallocated_memory(kinfo, ext_regions);
>          else
> @@ -1175,6 +1173,14 @@ static int __init make_hypervisor_node(struct domain
> *d,
> 
>          if ( res )
>              printk(XENLOG_WARNING "Failed to allocate extended regions\n");
> +        nr_ext_regions = ext_regions->nr_banks;
> +    }
> +
> +    reg = xzalloc_array(__be32, (nr_ext_regions + 1) * (addrcells +
> sizecells));
> +    if ( !reg )
> +    {
> +        xfree(ext_regions);
> +        return -ENOMEM;
>      }
> 
>      /* reg 0 is grant table space */
> @@ -1182,7 +1188,7 @@ static int __init make_hypervisor_node(struct domain *d,
>      dt_child_set_range(&cells, addrcells, sizecells,
>                         kinfo->gnttab_start, kinfo->gnttab_size);
>      /* reg 1...N are extended regions */
> -    for ( i = 0; i < ext_regions->nr_banks; i++ )
> +    for ( i = 0; i < nr_ext_regions; i++ )
>      {
>          u64 start = ext_regions->bank[i].start;
>          u64 size = ext_regions->bank[i].size;
> @@ -1195,7 +1201,7 @@ static int __init make_hypervisor_node(struct domain *d,
> 
>      res = fdt_property(fdt, "reg", reg,
>                         dt_cells_to_size(addrcells + sizecells) *
> -                       (ext_regions->nr_banks + 1));
> +                       (nr_ext_regions + 1));
>      xfree(ext_regions);
>      xfree(reg);
> 

Yep, that's what I meant, thanks