Messages in this thread | | | Date | Mon, 4 Apr 2022 19:40:24 +0530 | Subject | Re: [PATCH] arm64: mm: fix pmd_leaf() | From | Aneesh Kumar K V <> |
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On 4/4/22 5:10 PM, Muchun Song wrote: > On Mon, Apr 4, 2022 at 5:20 PM Will Deacon <will@kernel.org> wrote: >> >> On Sun, Apr 03, 2022 at 10:49:28AM +0800, Muchun Song wrote: >>> The pmd_leaf() is used to test a leaf mapped PMD, however, it misses >>> the PROT_NONE mapped PMD on arm64. Fix it. A real world issue [1] >>> caused by this was reported by Qian Cai. >>> >>> Link: https://patchwork.kernel.org/comment/24798260/ [1] >>> Fixes: 8aa82df3c123 ("arm64: mm: add p?d_leaf() definitions") >>> Reported-by: Qian Cai <quic_qiancai@quicinc.com> >>> Signed-off-by: Muchun Song <songmuchun@bytedance.com> >>> --- >>> arch/arm64/include/asm/pgtable.h | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h >>> index 94e147e5456c..09eaae46a19b 100644 >>> --- a/arch/arm64/include/asm/pgtable.h >>> +++ b/arch/arm64/include/asm/pgtable.h >>> @@ -535,7 +535,7 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn, >>> PMD_TYPE_TABLE) >>> #define pmd_sect(pmd) ((pmd_val(pmd) & PMD_TYPE_MASK) == \ >>> PMD_TYPE_SECT) >>> -#define pmd_leaf(pmd) pmd_sect(pmd) >>> +#define pmd_leaf(pmd) (pmd_present(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT)) >>> #define pmd_bad(pmd) (!pmd_table(pmd)) >>> >>> #define pmd_leaf_size(pmd) (pmd_cont(pmd) ? CONT_PMD_SIZE : PMD_SIZE) >> >> A bunch of the users of pmd_leaf() already check pmd_present() -- is it >> documented that we need to handle this check inside the macro? afaict x86 >> doesn't do this either.
ppc64 also doesn't do a pmd_present check.
>> > > arm64 is different from x86 here. pmd_leaf() could return true for > the none pmd without pmd_present() check, the check of > pmd_present() aims to exclude the pmd_none() case. However, > it could work properly on x86 without pmd_present() or pmd_none(). > So we don't see pmd_present() or pmd_none() check in pmd_leaf(). > For this reason, I think this check is necessary. > > BTW, there are some users of pmd_leaf() (e.g. apply_to_pmd_range, > walk_pmd_range, ptdump_pmd_entry) which do not check pmd_present() > or pmd_none() before the call of pmd_leaf(). So it is also necessary > to add the check. >
I would expect pmd_leaf check to return true, if the said pmd page table entry can point to a leaf page table entry which can also be a not present page table entry?
-aneesh
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