[PATCH -fixes] riscv: Do not allow vmap pud mappings for 3-level page table

[PATCH -fixes] riscv: Do not allow vmap pud mappings for 3-level page table

[Alexandre Ghiti]

The vmalloc_fault() path was removed and to avoid syncing the vmalloc PGD
mappings, they are now preallocated. But if the kernel can use a PUD
mapping (which in sv39 is actually a PGD mapping) for large vmalloc
allocation, it will free the current unused preallocated PGD mapping and
install a new leaf one. Since there is no sync anymore, some page tables
lack this new mapping and that triggers a panic.

So only allow PUD mappings for sv48 and sv57.

Fixes: 7d3332be011e ("riscv: mm: Pre-allocate PGD entries for vmalloc/modules area")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---
 arch/riscv/include/asm/vmalloc.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/vmalloc.h b/arch/riscv/include/asm/vmalloc.h
index 58d3e447f191..924d01b56c9a 100644
--- a/arch/riscv/include/asm/vmalloc.h
+++ b/arch/riscv/include/asm/vmalloc.h
@@ -3,12 +3,14 @@
 
 #ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
 
+extern bool pgtable_l4_enabled, pgtable_l5_enabled;
+
 #define IOREMAP_MAX_ORDER (PUD_SHIFT)
 
 #define arch_vmap_pud_supported arch_vmap_pud_supported
 static inline bool arch_vmap_pud_supported(pgprot_t prot)
 {
-	return true;
+	return pgtable_l4_enabled || pgtable_l5_enabled;
 }
 
 #define arch_vmap_pmd_supported arch_vmap_pmd_supported
-- 
2.39.2


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Re: [PATCH -fixes] riscv: Do not allow vmap pud mappings for 3-level page table

[patchwork-bot+linux-riscv]

Hello:

This patch was applied to riscv/linux.git (fixes)
by Palmer Dabbelt <palmer@rivosinc.com>:

On Tue,  8 Aug 2023 15:07:09 +0200 you wrote:
> The vmalloc_fault() path was removed and to avoid syncing the vmalloc PGD
> mappings, they are now preallocated. But if the kernel can use a PUD
> mapping (which in sv39 is actually a PGD mapping) for large vmalloc
> allocation, it will free the current unused preallocated PGD mapping and
> install a new leaf one. Since there is no sync anymore, some page tables
> lack this new mapping and that triggers a panic.
> 
> [...]

Here is the summary with links:
  - [-fixes] riscv: Do not allow vmap pud mappings for 3-level page table
    https://git.kernel.org/riscv/c/d566bea4a638

You are awesome, thank you!
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