On 31.08.24 10:35, Barry Song wrote:
From: Barry Song <v-songbaohua@xxxxxxxx>
Hi Ryan, David,
it seems contpte_ptep_set_access_flags() has never advanced
pte pfn, and it is setting all entries' pfn to the first
subpage. But I feel quite strange we never have a bug reported.
Am I missing something?
Fixes: 4602e5757bcc ("arm64/mm: wire up PTE_CONT for user mappings")
Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
---
arch/arm64/mm/contpte.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c
index a3edced29ac1..10dcd2641184 100644
--- a/arch/arm64/mm/contpte.c
+++ b/arch/arm64/mm/contpte.c
@@ -421,8 +421,10 @@ int contpte_ptep_set_access_flags(struct vm_area_struct *vma,
ptep = contpte_align_down(ptep);
start_addr = addr = ALIGN_DOWN(addr, CONT_PTE_SIZE);
- for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE)
+ for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) {
__ptep_set_access_flags(vma, addr, ptep, entry, 0);
+ entry = pte_advance_pfn(entry, 1);
+ }
if (dirty)
__flush_tlb_range(vma, start_addr, addr,
Taking a closer look at __ptep_set_access_flags(), there is:
/* only preserve the access flags and write permission *
pte_val(entry) &= PTE_RDONLY | PTE_AF | PTE_WRITE | PTE_DIRTY;
So it looks like it doesn't need the PFN?
OTOH, there is the initial:
if (pte_same(pte, entry))
return 0;
check that might accelerate things.
So unless I am missing something, this works as expected? (and if the
pte_same() would frequently be taken with your change would be worthwile
to optimize)
--
Cheers,
David / dhildenb
