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From: Steven Price <steven.price@arm.com>
To: Will Deacon <will@kernel.org>, Muchun Song <songmuchun@bytedance.com>
Cc: catalin.marinas@arm.com, akpm@linux-foundation.org,
	anshuman.khandual@arm.com, aneesh.kumar@linux.ibm.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()
Date: Mon, 4 Apr 2022 11:51:13 +0100	[thread overview]
Message-ID: <14d1bb4c-f58b-12d6-1034-c851263acafd@arm.com> (raw)
In-Reply-To: <20220404091957.GA22790@willie-the-truck>

On 04/04/2022 10:19, Will Deacon 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.

The documentation is with the fallback implementations that always
return 0:

> /*
>  * p?d_leaf() - true if this entry is a final mapping to a physical address.
>  * This differs from p?d_huge() by the fact that they are always available (if
>  * the architecture supports large pages at the appropriate level) even
>  * if CONFIG_HUGETLB_PAGE is not defined.
>  * Only meaningful when called on a valid entry.
>  */

I guess the term "valid entry" is a bit vague but my intention was that
meant p?d_present().

I have to admit I hadn't considered PROT_NONE mappings before.

Steve

WARNING: multiple messages have this Message-ID (diff)
From: Steven Price <steven.price@arm.com>
To: Will Deacon <will@kernel.org>, Muchun Song <songmuchun@bytedance.com>
Cc: catalin.marinas@arm.com, akpm@linux-foundation.org,
	anshuman.khandual@arm.com, aneesh.kumar@linux.ibm.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()
Date: Mon, 4 Apr 2022 11:51:13 +0100	[thread overview]
Message-ID: <14d1bb4c-f58b-12d6-1034-c851263acafd@arm.com> (raw)
In-Reply-To: <20220404091957.GA22790@willie-the-truck>

On 04/04/2022 10:19, Will Deacon 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.

The documentation is with the fallback implementations that always
return 0:

> /*
>  * p?d_leaf() - true if this entry is a final mapping to a physical address.
>  * This differs from p?d_huge() by the fact that they are always available (if
>  * the architecture supports large pages at the appropriate level) even
>  * if CONFIG_HUGETLB_PAGE is not defined.
>  * Only meaningful when called on a valid entry.
>  */

I guess the term "valid entry" is a bit vague but my intention was that
meant p?d_present().

I have to admit I hadn't considered PROT_NONE mappings before.

Steve

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  reply	other threads:[~2022-04-04 10:51 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-03  2:49 [PATCH] arm64: mm: fix pmd_leaf() Muchun Song
2022-04-03  2:49 ` Muchun Song
2022-04-04  9:19 ` Will Deacon
2022-04-04  9:19   ` Will Deacon
2022-04-04 10:51   ` Steven Price [this message]
2022-04-04 10:51     ` Steven Price
2022-04-04 11:40   ` Muchun Song
2022-04-04 11:40     ` Muchun Song
2022-04-04 14:10     ` Aneesh Kumar K V
2022-04-04 14:10       ` Aneesh Kumar K V
2022-04-04 15:24       ` Muchun Song
2022-04-04 15:24         ` Muchun Song

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