Messages in this thread | | | From | Muchun Song <> | Date | Mon, 4 Apr 2022 19:40:05 +0800 | Subject | Re: [PATCH] arm64: mm: fix pmd_leaf() |
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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. >
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.
Thanks.
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