Messages in this thread | | | From | Muchun Song <> | Date | Mon, 4 Apr 2022 23:24:01 +0800 | Subject | Re: [PATCH] arm64: mm: fix pmd_leaf() |
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On Mon, Apr 4, 2022 at 10:10 PM Aneesh Kumar K V <aneesh.kumar@linux.ibm.com> wrote: > > 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? >
All right. In order to exclude the pmd_none() case. How about the following code?
#define pmd_leaf(pmd) (pmd_val(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT))
Thanks.
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