Set up fixmap mappings and the L0 page table for fixmap support.

Modify the Page Table Entries (PTEs) directly in arch_pmap_map()
instead of using set_fixmap() ( which relies on map_pages_to_xen() ).
This change is necessary because PMAP is used when the domain map
page infrastructure is not yet initialized so map_pages_to_xen()
called by set_fixmap() needs to map pages on demand, which then
calls pmap() again, resulting in a loop.
The same reasoning applies to pmap_unmap(), which also modifies
PTEs directly to avoid this issue.

Define new macros in riscv/config.h for calculating
the FIXMAP_BASE address, including BOOT_FDT_VIRT_{START, SIZE},
XEN_VIRT_SIZE, and XEN_VIRT_END.

Update the check for Xen size in riscv/lds.S to use
XEN_VIRT_SIZE instead of a hardcoded constant.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
---
Changes in V6:
 - avoid case mixing for address in RISC-V64 layout table.
 - move definition of FIXMAP_BASE to new line.
 - update the commit message.
---
Changes in V5:
 - move definition of FIXMAP_ADDR() to asm/fixmap.h
 - add gap size equal to 2 MB ( 512 * 4K one page table entry in L1 page table )
   between Xen, FDT and Fixmap.
 - drop the comment for FIX_LAST.
 - move +1 from FIX_LAST definition to FIXADDR_TOP to be aligned with Arm.
   ( probably everything below FIX_LAST will be moved to a separate header in asm/generic.h )
 - correct the "changes in V4: s/'fence r,r'/'fence rw, rw'
 - use write_atomic() in set_pte().
 - introduce read_pte().
---
Changes in V4:
 - move definitions of XEN_VIRT_SIZE, BOOT_FDT_VIRT_{START,SIZE}, FIXMAP_{BASE,ADDR}
   below XEN_VIRT_START to have definitions appear in order.
 - define FIX_LAST as (FIX_MISC + 1) to have a guard slot at the end.
 - s/enumerated/numbered in the comment
 - update the cycle which looks for L1 page table in setup_fixmap_mapping_function() and
   the comment above him.
 - drop fences inside write_pte() and put 'fence rw,rw' in setup_fixmap() before sfence_vma().
 - update the commit message
 - drop printk message inside setup_fixmap().
---
Changes in V3:
 - s/XEN_SIZE/XEN_VIRT_SIZE
 - drop usage of XEN_VIRT_END.
 - sort newly introduced defines in config.h by address
 - code style fixes
 - drop runtime check of that pte is valid as it was checked in L1 page table finding cycle by BUG_ON().
 - update implementation of write_pte() with FENCE rw, rw.
 - add BUILD_BUG_ON() to check that amount of entries aren't bigger then entries in page table.
 - drop set_fixmap, clear_fixmap declarations as they aren't used and defined now
 - update the commit message.
 - s/__ASM_FIXMAP_H/ASM_FIXMAP_H
 - add SPDX-License-Identifier: GPL-2.0 
---
 xen/arch/riscv/include/asm/config.h | 16 ++++++++--
 xen/arch/riscv/include/asm/fixmap.h | 46 +++++++++++++++++++++++++++++
 xen/arch/riscv/include/asm/mm.h     |  2 ++
 xen/arch/riscv/include/asm/page.h   | 13 ++++++++
 xen/arch/riscv/mm.c                 | 43 +++++++++++++++++++++++++++
 xen/arch/riscv/setup.c              |  2 ++
 xen/arch/riscv/xen.lds.S            |  2 +-
 7 files changed, 121 insertions(+), 3 deletions(-)
 create mode 100644 xen/arch/riscv/include/asm/fixmap.h

diff --git a/xen/arch/riscv/include/asm/config.h b/xen/arch/riscv/include/asm/config.h
index 50583aafdc..7dbb235685 100644
--- a/xen/arch/riscv/include/asm/config.h
+++ b/xen/arch/riscv/include/asm/config.h
@@ -41,8 +41,10 @@
  * Start addr          | End addr         | Slot       | area description
  * ============================================================================
  *                   .....                 L2 511          Unused
- *  0xffffffffc0600000  0xffffffffc0800000 L2 511          Fixmap
- *  0xffffffffc0200000  0xffffffffc0600000 L2 511          FDT
+ *  0xffffffffc0a00000  0xffffffffc0c00000 L2 511          Fixmap
+ *                   ..... ( 2 MB gap )
+ *  0xffffffffc0400000  0xffffffffc0800000 L2 511          FDT
+ *                   ..... ( 2 MB gap )
  *  0xffffffffc0000000  0xffffffffc0200000 L2 511          Xen
  *                   .....                 L2 510          Unused
  *  0x3200000000        0x7f40000000       L2 200-509      Direct map
@@ -74,6 +76,16 @@
 #error "unsupported RV_STAGE1_MODE"
 #endif
 
+#define GAP_SIZE                MB(2)
+
+#define XEN_VIRT_SIZE           MB(2)
+
+#define BOOT_FDT_VIRT_START     (XEN_VIRT_START + XEN_VIRT_SIZE + GAP_SIZE)
+#define BOOT_FDT_VIRT_SIZE      MB(4)
+
+#define FIXMAP_BASE \
+    (BOOT_FDT_VIRT_START + BOOT_FDT_VIRT_SIZE + GAP_SIZE)
+
 #define DIRECTMAP_SLOT_END      509
 #define DIRECTMAP_SLOT_START    200
 #define DIRECTMAP_VIRT_START    SLOTN(DIRECTMAP_SLOT_START)
diff --git a/xen/arch/riscv/include/asm/fixmap.h b/xen/arch/riscv/include/asm/fixmap.h
new file mode 100644
index 0000000000..63732df36c
--- /dev/null
+++ b/xen/arch/riscv/include/asm/fixmap.h
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * fixmap.h: compile-time virtual memory allocation
+ */
+#ifndef ASM_FIXMAP_H
+#define ASM_FIXMAP_H
+
+#include <xen/bug.h>
+#include <xen/page-size.h>
+#include <xen/pmap.h>
+
+#include <asm/page.h>
+
+#define FIXMAP_ADDR(n) (FIXMAP_BASE + (n) * PAGE_SIZE)
+
+/* Fixmap slots */
+#define FIX_PMAP_BEGIN (0) /* Start of PMAP */
+#define FIX_PMAP_END (FIX_PMAP_BEGIN + NUM_FIX_PMAP - 1) /* End of PMAP */
+#define FIX_MISC (FIX_PMAP_END + 1)  /* Ephemeral mappings of hardware */
+
+#define FIX_LAST FIX_MISC
+
+#define FIXADDR_START FIXMAP_ADDR(0)
+#define FIXADDR_TOP FIXMAP_ADDR(FIX_LAST + 1)
+
+#ifndef __ASSEMBLY__
+
+/*
+ * Direct access to xen_fixmap[] should only happen when {set,
+ * clear}_fixmap() is unusable (e.g. where we would end up to
+ * recursively call the helpers).
+ */
+extern pte_t xen_fixmap[];
+
+#define fix_to_virt(slot) ((void *)FIXMAP_ADDR(slot))
+
+static inline unsigned int virt_to_fix(vaddr_t vaddr)
+{
+    BUG_ON(vaddr >= FIXADDR_TOP || vaddr < FIXADDR_START);
+
+    return ((vaddr - FIXADDR_START) >> PAGE_SHIFT);
+}
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* ASM_FIXMAP_H */
diff --git a/xen/arch/riscv/include/asm/mm.h b/xen/arch/riscv/include/asm/mm.h
index 25af9e1aaa..a0bdc2bc3a 100644
--- a/xen/arch/riscv/include/asm/mm.h
+++ b/xen/arch/riscv/include/asm/mm.h
@@ -255,4 +255,6 @@ static inline unsigned int arch_get_dma_bitsize(void)
     return 32; /* TODO */
 }
 
+void setup_fixmap_mappings(void);
+
 #endif /* _ASM_RISCV_MM_H */
diff --git a/xen/arch/riscv/include/asm/page.h b/xen/arch/riscv/include/asm/page.h
index c831e16417..a7419b93b2 100644
--- a/xen/arch/riscv/include/asm/page.h
+++ b/xen/arch/riscv/include/asm/page.h
@@ -9,6 +9,7 @@
 #include <xen/bug.h>
 #include <xen/types.h>
 
+#include <asm/atomic.h>
 #include <asm/mm.h>
 #include <asm/page-bits.h>
 
@@ -81,6 +82,18 @@ static inline void flush_page_to_ram(unsigned long mfn, bool sync_icache)
     BUG_ON("unimplemented");
 }
 
+/* Write a pagetable entry. */
+static inline void write_pte(pte_t *p, pte_t pte)
+{
+    write_atomic(p, pte);
+}
+
+/* Read a pagetable entry. */
+static inline pte_t read_pte(pte_t *p)
+{
+    return read_atomic(p);
+}
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_RISCV_PAGE_H */
diff --git a/xen/arch/riscv/mm.c b/xen/arch/riscv/mm.c
index 7d09e781bf..b8ff91cf4e 100644
--- a/xen/arch/riscv/mm.c
+++ b/xen/arch/riscv/mm.c
@@ -12,6 +12,7 @@
 #include <asm/early_printk.h>
 #include <asm/csr.h>
 #include <asm/current.h>
+#include <asm/fixmap.h>
 #include <asm/page.h>
 #include <asm/processor.h>
 
@@ -49,6 +50,9 @@ stage1_pgtbl_root[PAGETABLE_ENTRIES];
 pte_t __section(".bss.page_aligned") __aligned(PAGE_SIZE)
 stage1_pgtbl_nonroot[PGTBL_INITIAL_COUNT * PAGETABLE_ENTRIES];
 
+pte_t __section(".bss.page_aligned") __aligned(PAGE_SIZE)
+xen_fixmap[PAGETABLE_ENTRIES];
+
 #define HANDLE_PGTBL(curr_lvl_num)                                          \
     index = pt_index(curr_lvl_num, page_addr);                              \
     if ( pte_is_valid(pgtbl[index]) )                                       \
@@ -191,6 +195,45 @@ static bool __init check_pgtbl_mode_support(struct mmu_desc *mmu_desc,
     return is_mode_supported;
 }
 
+void __init setup_fixmap_mappings(void)
+{
+    pte_t *pte, tmp;
+    unsigned int i;
+
+    BUILD_BUG_ON(FIX_LAST >= PAGETABLE_ENTRIES);
+
+    pte = &stage1_pgtbl_root[pt_index(HYP_PT_ROOT_LEVEL, FIXMAP_ADDR(0))];
+
+    /*
+     * In RISC-V page table levels are numbered from Lx to L0 where
+     * x is the highest page table level for currect  MMU mode ( for example,
+     * for Sv39 has 3 page tables so the x = 2 (L2 -> L1 -> L0) ).
+     *
+     * In this cycle we want to find L1 page table because as L0 page table
+     * xen_fixmap[] will be used.
+     */
+    for ( i = HYP_PT_ROOT_LEVEL; i-- > 1; )
+    {
+        BUG_ON(!pte_is_valid(*pte));
+
+        pte = (pte_t *)LOAD_TO_LINK(pte_to_paddr(*pte));
+        pte = &pte[pt_index(i, FIXMAP_ADDR(0))];
+    }
+
+    BUG_ON(pte_is_valid(*pte));
+
+    tmp = paddr_to_pte(LINK_TO_LOAD((unsigned long)&xen_fixmap), PTE_TABLE);
+    write_pte(pte, tmp);
+
+    RISCV_FENCE(rw, rw);
+    sfence_vma();
+
+    /*
+     * We only need the zeroeth table allocated, but not the PTEs set, because
+     * set_fixmap() will set them on the fly.
+     */
+}
+
 /*
  * setup_initial_pagetables:
  *
diff --git a/xen/arch/riscv/setup.c b/xen/arch/riscv/setup.c
index 4defad68f4..13f0e8c77d 100644
--- a/xen/arch/riscv/setup.c
+++ b/xen/arch/riscv/setup.c
@@ -46,6 +46,8 @@ void __init noreturn start_xen(unsigned long bootcpu_id,
     test_macros_from_bug_h();
 #endif
 
+    setup_fixmap_mappings();
+
     printk("All set up\n");
 
     for ( ;; )
diff --git a/xen/arch/riscv/xen.lds.S b/xen/arch/riscv/xen.lds.S
index 070b19d915..7a683f6065 100644
--- a/xen/arch/riscv/xen.lds.S
+++ b/xen/arch/riscv/xen.lds.S
@@ -181,6 +181,6 @@ ASSERT(!SIZEOF(.got.plt),  ".got.plt non-empty")
  * Changing the size of Xen binary can require an update of
  * PGTBL_INITIAL_COUNT.
  */
-ASSERT(_end - _start <= MB(2), "Xen too large for early-boot assumptions")
+ASSERT(_end - _start <= XEN_VIRT_SIZE, "Xen too large for early-boot assumptions")
 
 ASSERT(_ident_end - _ident_start <= IDENT_AREA_SIZE, "identity region is too big");
-- 
2.46.0

On 02.09.2024 19:01, Oleksii Kurochko wrote:
> Set up fixmap mappings and the L0 page table for fixmap support.
> 
> Modify the Page Table Entries (PTEs) directly in arch_pmap_map()
> instead of using set_fixmap() ( which relies on map_pages_to_xen() ).

What do you derive this from? There's no set_fixmap() here, and hence
it's unknown how it is going to be implemented. The most you can claim
is that it is expected that it will use map_pages_to_xen(), which in
turn ...

> This change is necessary because PMAP is used when the domain map
> page infrastructure is not yet initialized so map_pages_to_xen()
> called by set_fixmap() needs to map pages on demand, which then
> calls pmap() again, resulting in a loop.

... is only expected to use arch_pmap_map().

> @@ -81,6 +82,18 @@ static inline void flush_page_to_ram(unsigned long mfn, bool sync_icache)
>      BUG_ON("unimplemented");
>  }
>  
> +/* Write a pagetable entry. */
> +static inline void write_pte(pte_t *p, pte_t pte)
> +{
> +    write_atomic(p, pte);
> +}
> +
> +/* Read a pagetable entry. */
> +static inline pte_t read_pte(pte_t *p)

const pte_t *?

Jan

On Tue, 2024-09-10 at 12:01 +0200, Jan Beulich wrote:
> On 02.09.2024 19:01, Oleksii Kurochko wrote:
> > Set up fixmap mappings and the L0 page table for fixmap support.
> > 
> > Modify the Page Table Entries (PTEs) directly in arch_pmap_map()
> > instead of using set_fixmap() ( which relies on map_pages_to_xen()
> > ).
> 
> What do you derive this from? There's no set_fixmap() here, and hence
> it's unknown how it is going to be implemented.
I derived it from the my code where is set_fixmap() is implemented but
agree that in brackets it is better to write "will use
map_pages_to_xen()" instead of "which relies on map_pages_to_xen()".

>  The most you can claim
> is that it is expected that it will use map_pages_to_xen(), which in
> turn ...
> 
> > This change is necessary because PMAP is used when the domain map
> > page infrastructure is not yet initialized so map_pages_to_xen()
> > called by set_fixmap() needs to map pages on demand, which then
> > calls pmap() again, resulting in a loop.
> 
> ... is only expected to use arch_pmap_map().
it is what is written in the message, isn't it? But I am okay to change
this part of the commit message to:
   {set, clear}_fixmap() is expected to be implemented using
   map_pages_to_xen(), which, in turn, is only expected to use
   arch_pmap_map().

> 
> > @@ -81,6 +82,18 @@ static inline void flush_page_to_ram(unsigned
> > long mfn, bool sync_icache)
> >      BUG_ON("unimplemented");
> >  }
> >  
> > +/* Write a pagetable entry. */
> > +static inline void write_pte(pte_t *p, pte_t pte)
> > +{
> > +    write_atomic(p, pte);
> > +}
> > +
> > +/* Read a pagetable entry. */
> > +static inline pte_t read_pte(pte_t *p)
> 
> const pte_t *?
It would be better to make it const. Thanks.

~ Oleksii

On 10.09.2024 17:55, oleksii.kurochko@gmail.com wrote:
> On Tue, 2024-09-10 at 12:01 +0200, Jan Beulich wrote:
>> On 02.09.2024 19:01, Oleksii Kurochko wrote:
>>> Set up fixmap mappings and the L0 page table for fixmap support.
>>>
>>> Modify the Page Table Entries (PTEs) directly in arch_pmap_map()
>>> instead of using set_fixmap() ( which relies on map_pages_to_xen()
>>> ).
>>
>> What do you derive this from? There's no set_fixmap() here, and hence
>> it's unknown how it is going to be implemented.
> I derived it from the my code where is set_fixmap() is implemented but
> agree that in brackets it is better to write "will use
> map_pages_to_xen()" instead of "which relies on map_pages_to_xen()".
> 
>>  The most you can claim
>> is that it is expected that it will use map_pages_to_xen(), which in
>> turn ...
>>
>>> This change is necessary because PMAP is used when the domain map
>>> page infrastructure is not yet initialized so map_pages_to_xen()
>>> called by set_fixmap() needs to map pages on demand, which then
>>> calls pmap() again, resulting in a loop.
>>
>> ... is only expected to use arch_pmap_map().
> it is what is written in the message, isn't it?

Not quite - the original sentence is written as if map_pages_to_xen()
existed already in the code base, or was brought into existence by
this very patch. (Of course I mean the real function, not the stub
that's there.)

Jan