From: Luca Fancellu <luca.fancellu@arm.com>
Implement the function early_fdt_map(), which is responsible for mapping
the Device Tree Blob in the early stages of the boot process, for MPU
systems.
We make use of the map_pages_to_xen() and destroy_xen_mappings() APIs.
In particular the latter function is necessary in the case that the
initial mapping of the fdt_header is insufficient to cover the entire
DTB, as we must destroy and then remap the region due to the APIs no
providing support for extending the size of an existing region.
Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>
Signed-off-by: Hari Limaye <hari.limaye@arm.com>
Reviewed-by: Ayan Kumar Halder <ayan.kumar.halder@amd.com>
---
Changes from v1:
- Add Ayan's R-b
---
xen/arch/arm/mpu/setup.c | 74 ++++++++++++++++++++++++++++++++++++++--
1 file changed, 72 insertions(+), 2 deletions(-)
diff --git a/xen/arch/arm/mpu/setup.c b/xen/arch/arm/mpu/setup.c
index b4da77003f..ab00cb944b 100644
--- a/xen/arch/arm/mpu/setup.c
+++ b/xen/arch/arm/mpu/setup.c
@@ -1,17 +1,87 @@
/* SPDX-License-Identifier: GPL-2.0-only */
+#include <xen/bootfdt.h>
#include <xen/bug.h>
#include <xen/init.h>
+#include <xen/libfdt/libfdt.h>
#include <xen/mm.h>
+#include <xen/pfn.h>
#include <xen/types.h>
#include <asm/setup.h>
+static paddr_t __initdata mapped_fdt_paddr = INVALID_PADDR;
+static paddr_t __initdata mapped_fdt_limit = INVALID_PADDR;
+
void __init setup_pagetables(void) {}
void * __init early_fdt_map(paddr_t fdt_paddr)
{
- BUG_ON("unimplemented");
- return NULL;
+ /* Map at least a page containing the DTB address, exclusive range */
+ paddr_t base = round_pgdown(fdt_paddr);
+ paddr_t limit = round_pgup(fdt_paddr + sizeof(struct fdt_header));
+ unsigned int flags = PAGE_HYPERVISOR_RO;
+ void *fdt_virt = (void *)fdt_paddr; /* virt == paddr for MPU */
+ int rc;
+ unsigned long nr_mfns;
+
+ /*
+ * Check whether the physical FDT address is set and meets the minimum
+ * alignment requirement. Since we are relying on MIN_FDT_ALIGN to be at
+ * least 8 bytes so that we always access the magic and size fields
+ * of the FDT header after mapping the first chunk, double check if
+ * that is indeed the case.
+ */
+ BUILD_BUG_ON(MIN_FDT_ALIGN < 8);
+ if ( !fdt_paddr || fdt_paddr % MIN_FDT_ALIGN )
+ return NULL;
+
+ /* DTB starting at this address has already been mapped. */
+ if ( mapped_fdt_paddr == fdt_paddr )
+ return fdt_virt;
+
+ /*
+ * DTB starting at a different address has been mapped, so destroy this
+ * before continuing.
+ */
+ if ( mapped_fdt_paddr != INVALID_PADDR )
+ {
+ rc = destroy_xen_mappings(round_pgdown(mapped_fdt_paddr),
+ mapped_fdt_limit);
+ if ( rc )
+ panic("Unable to unmap existing device-tree.\n");
+ }
+
+ nr_mfns = (limit - base) >> PAGE_SHIFT;
+
+ rc = map_pages_to_xen(base, maddr_to_mfn(base), nr_mfns, flags);
+ if ( rc )
+ panic("Unable to map the device-tree.\n");
+
+ mapped_fdt_paddr = fdt_paddr;
+ mapped_fdt_limit = limit;
+
+ if ( fdt_magic(fdt_virt) != FDT_MAGIC )
+ return NULL;
+
+ limit = round_pgup(fdt_paddr + fdt_totalsize(fdt_virt));
+
+ /* If the mapped range is not enough, map the rest of the DTB. */
+ if ( limit > mapped_fdt_limit )
+ {
+ rc = destroy_xen_mappings(base, mapped_fdt_limit);
+ if ( rc )
+ panic("Unable to unmap the device-tree header.\n");
+
+ nr_mfns = (limit - base) >> PAGE_SHIFT;
+
+ rc = map_pages_to_xen(base, maddr_to_mfn(base), nr_mfns, flags);
+ if ( rc )
+ panic("Unable to map the device-tree.\n");
+
+ mapped_fdt_limit = limit;
+ }
+
+ return fdt_virt;
}
/*
--
2.34.1
On 02/07/2025 16:14, Hari Limaye wrote:
> From: Luca Fancellu <luca.fancellu@arm.com>
>
> Implement the function early_fdt_map(), which is responsible for mapping
> the Device Tree Blob in the early stages of the boot process, for MPU
> systems.
>
> We make use of the map_pages_to_xen() and destroy_xen_mappings() APIs.
> In particular the latter function is necessary in the case that the
> initial mapping of the fdt_header is insufficient to cover the entire
> DTB, as we must destroy and then remap the region due to the APIs no
> providing support for extending the size of an existing region.
>
> Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>
> Signed-off-by: Hari Limaye <hari.limaye@arm.com>
> Reviewed-by: Ayan Kumar Halder <ayan.kumar.halder@amd.com>
> ---
> Changes from v1:
> - Add Ayan's R-b
> ---
> xen/arch/arm/mpu/setup.c | 74 ++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 72 insertions(+), 2 deletions(-)
>
> diff --git a/xen/arch/arm/mpu/setup.c b/xen/arch/arm/mpu/setup.c
> index b4da77003f..ab00cb944b 100644
> --- a/xen/arch/arm/mpu/setup.c
> +++ b/xen/arch/arm/mpu/setup.c
> @@ -1,17 +1,87 @@
> /* SPDX-License-Identifier: GPL-2.0-only */
>
> +#include <xen/bootfdt.h>
> #include <xen/bug.h>
> #include <xen/init.h>
> +#include <xen/libfdt/libfdt.h>
> #include <xen/mm.h>
> +#include <xen/pfn.h>
> #include <xen/types.h>
> #include <asm/setup.h>
>
> +static paddr_t __initdata mapped_fdt_paddr = INVALID_PADDR;
I think it would be better to name it mapped_fdt_base, given that in MPU
everything refers to base,limit.
> +static paddr_t __initdata mapped_fdt_limit = INVALID_PADDR;
> +
> void __init setup_pagetables(void) {}
>
> void * __init early_fdt_map(paddr_t fdt_paddr)
> {
> - BUG_ON("unimplemented");
> - return NULL;
> + /* Map at least a page containing the DTB address, exclusive range */
> + paddr_t base = round_pgdown(fdt_paddr);
> + paddr_t limit = round_pgup(fdt_paddr + sizeof(struct fdt_header));
> + unsigned int flags = PAGE_HYPERVISOR_RO;
> + void *fdt_virt = (void *)fdt_paddr; /* virt == paddr for MPU */
> + int rc;
> + unsigned long nr_mfns;
> +
> + /*
> + * Check whether the physical FDT address is set and meets the minimum
> + * alignment requirement. Since we are relying on MIN_FDT_ALIGN to be at
> + * least 8 bytes so that we always access the magic and size fields
> + * of the FDT header after mapping the first chunk, double check if
> + * that is indeed the case.
> + */
> + BUILD_BUG_ON(MIN_FDT_ALIGN < 8);
> + if ( !fdt_paddr || fdt_paddr % MIN_FDT_ALIGN )
> + return NULL;
> +
> + /* DTB starting at this address has already been mapped. */
When can this happen?
> + if ( mapped_fdt_paddr == fdt_paddr )
> + return fdt_virt;
> +
> + /*
> + * DTB starting at a different address has been mapped, so destroy this
> + * before continuing.
> + */
> + if ( mapped_fdt_paddr != INVALID_PADDR )
> + {
> + rc = destroy_xen_mappings(round_pgdown(mapped_fdt_paddr),
> + mapped_fdt_limit);
> + if ( rc )
> + panic("Unable to unmap existing device-tree.\n");
NIT: no need for a dot at the end. It only takes space and is really not needed.
> + }
> +
> + nr_mfns = (limit - base) >> PAGE_SHIFT;
> +
> + rc = map_pages_to_xen(base, maddr_to_mfn(base), nr_mfns, flags);
> + if ( rc )
> + panic("Unable to map the device-tree.\n");
> +
> + mapped_fdt_paddr = fdt_paddr;
> + mapped_fdt_limit = limit;
> +
> + if ( fdt_magic(fdt_virt) != FDT_MAGIC )
> + return NULL;
> +
> + limit = round_pgup(fdt_paddr + fdt_totalsize(fdt_virt));
You're missing a sanity check for MAX_FDT_SIZE
> +
> + /* If the mapped range is not enough, map the rest of the DTB. */
> + if ( limit > mapped_fdt_limit )
> + {
> + rc = destroy_xen_mappings(base, mapped_fdt_limit);
> + if ( rc )
> + panic("Unable to unmap the device-tree header.\n");
> +
> + nr_mfns = (limit - base) >> PAGE_SHIFT;
> +
> + rc = map_pages_to_xen(base, maddr_to_mfn(base), nr_mfns, flags);
> + if ( rc )
> + panic("Unable to map the device-tree.\n");
> +
> + mapped_fdt_limit = limit;
> + }
> +
> + return fdt_virt;
> }
>
> /*
~Michal
Hi Michal, Thank you for reviewing the patch. To answer the following question: > > + /* DTB starting at this address has already been mapped. */ > When can this happen? In xen/arch/arm/setup.c `start_xen` early_fdt_map(fdt_paddr) is called twice, before and after `setup_page_tables` - which is a no-op on an MPU system. This seemed like the neatest way to handle this - but maybe you'd prefer further clarification in the comment here? Many thanks, Hari
On 11/07/2025 08:05, Hari Limaye wrote: > Hi Michal, > > > > Thank you for reviewing the patch. To answer the following question: > >> > + /* DTB starting at this address has already been mapped. */ > >> When can this happen? > > > > In xen/arch/arm/setup.c `start_xen` early_fdt_map(fdt_paddr) is called twice, > > before and after `setup_page_tables` - which is a no-op on an MPU system. This > > seemed like the neatest way to handle this - but maybe you'd prefer further > > clarification in the comment here? Yes, I would like this comment to be improved a bit. ~Michal
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