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Date:   Mon, 4 Apr 2022 10:19:58 +0100
From:   Will Deacon <will@kernel.org>
To:     Muchun Song <songmuchun@bytedance.com>
Cc:     catalin.marinas@arm.com, akpm@linux-foundation.org,
        anshuman.khandual@arm.com, aneesh.kumar@linux.ibm.com,
        steven.price@arm.com, lengxujun2007@126.com, arnd@arndb.de,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        smuchun@gmail.com, duanxiongchun@bytedance.com,
        Qian Cai <quic_qiancai@quicinc.com>
Subject: Re: [PATCH] arm64: mm: fix pmd_leaf()
Message-ID: <20220404091957.GA22790@willie-the-truck>
References: <20220403024928.4125-1-songmuchun@bytedance.com>
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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.

Will