Re: [PATCH] arm64: mm: fix pmd_leaf()

[Will Deacon]

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@xxxxxxxxxxx>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
>  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.

Will