Re: [PATCH -next v5 3/5] mm: page_table_check: add hooks to public helpers

[Tong Tiangen <tongtiangen@huawei.com>]

在 2022/4/22 14:05, Anshuman Khandual 写道:
> 
> 
> On 4/21/22 13:50, Tong Tiangen wrote:
>> Move ptep_clear() to the include/linux/pgtable.h and add page table check
>> relate hooks to some helpers, it's prepare for support page table check
>> feature on new architecture.
> 
> Could instrumenting generic page table helpers (fallback instances when its
> corresponding __HAVE_ARCH_XXX is not defined on the platform), might add all
> the page table check hooks into paths on platforms which have not subscribed
> ARCH_SUPPORTS_PAGE_TABLE_CHECK in the first place ? Although these looks have
> !CONFIG_PAGE_TABLE_CHECK fallback stubs in the header, hence a build problem
> gets avoided.

Right, build problems are avoided by fallback stubs in the header file.

> 
>>
>> Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
>> Acked-by: Pasha Tatashin <pasha.tatashin@soleen.com>
>> ---
>>   arch/x86/include/asm/pgtable.h | 10 ----------
>>   include/linux/pgtable.h        | 26 ++++++++++++++++++--------
>>   2 files changed, 18 insertions(+), 18 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
>> index 564abe42b0f7..51cd39858f81 100644
>> --- a/arch/x86/include/asm/pgtable.h
>> +++ b/arch/x86/include/asm/pgtable.h
>> @@ -1073,16 +1073,6 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
>>   	return pte;
>>   }
>>   
>> -#define __HAVE_ARCH_PTEP_CLEAR
> 
> AFICS X86 is the only platform subscribing __HAVE_ARCH_PTEP_CLEAR. Hence if
> this is getting dropped for generic ptep_clear(), then no need to add back
> #ifnded __HAVE_ARCH_PTEP_CLEAR construct. Generic ptep_clear() is the only
> definition for all platforms ?
> 
> Also if this patch is trying to drop off __HAVE_ARCH_PTEP_CLEAR along with
> other page table check related changes, it needs to be done via a separate
> patch instead.

Agreed.
IMO, this fix can be patched later.

> 
>> -static inline void ptep_clear(struct mm_struct *mm, unsigned long addr,
>> -			      pte_t *ptep)
>> -{
>> -	if (IS_ENABLED(CONFIG_PAGE_TABLE_CHECK))
>> -		ptep_get_and_clear(mm, addr, ptep);
>> -	else
>> -		pte_clear(mm, addr, ptep);
>> -}
>> -
>>   #define __HAVE_ARCH_PTEP_SET_WRPROTECT
>>   static inline void ptep_set_wrprotect(struct mm_struct *mm,
>>   				      unsigned long addr, pte_t *ptep)
>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>> index 49ab8ee2d6d7..10d2d91edf20 100644
>> --- a/include/linux/pgtable.h
>> +++ b/include/linux/pgtable.h
>> @@ -12,6 +12,7 @@
>>   #include <linux/bug.h>
>>   #include <linux/errno.h>
>>   #include <asm-generic/pgtable_uffd.h>
>> +#include <linux/page_table_check.h>
>>   
>>   #if 5 - defined(__PAGETABLE_P4D_FOLDED) - defined(__PAGETABLE_PUD_FOLDED) - \
>>   	defined(__PAGETABLE_PMD_FOLDED) != CONFIG_PGTABLE_LEVELS
>> @@ -272,14 +273,6 @@ static inline bool arch_has_hw_pte_young(void)
>>   }
>>   #endif
>>   
>> -#ifndef __HAVE_ARCH_PTEP_CLEAR
>> -static inline void ptep_clear(struct mm_struct *mm, unsigned long addr,
>> -			      pte_t *ptep)
>> -{
>> -	pte_clear(mm, addr, ptep);
>> -}
>> -#endif
>> -
>>   #ifndef __HAVE_ARCH_PTEP_GET_AND_CLEAR
>>   static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
>>   				       unsigned long address,
>> @@ -287,10 +280,22 @@ static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
>>   {
>>   	pte_t pte = *ptep;
>>   	pte_clear(mm, address, ptep);
>> +	page_table_check_pte_clear(mm, address, pte);
>>   	return pte;
>>   }
>>   #endif
>>   
>> +#ifndef __HAVE_ARCH_PTEP_CLEAR
>> +static inline void ptep_clear(struct mm_struct *mm, unsigned long addr,
>> +			      pte_t *ptep)
>> +{
>> +	if (IS_ENABLED(CONFIG_PAGE_TABLE_CHECK))
>> +		ptep_get_and_clear(mm, addr, ptep);
>> +	else
>> +		pte_clear(mm, addr, ptep);
> 
> Could not this be reworked to avoid IS_ENABLED() ? This is confusing. If the page
> table hooks can be added to all potential page table paths via generic helpers,
> irrespective of CONFIG_PAGE_TABLE_CHECK option, there is no rationale for doing
> a IS_ENABLED() check here.
> 

 From the perspective of code logic, we need to check the pte before 
being cleared. Whether pte check is required depends on IS_ENABLED().

Are there any suggestions for better implementation?

Thank you,
Tong.

>> +}
>> +#endif
>> +
>>   #ifndef __HAVE_ARCH_PTEP_GET
>>   static inline pte_t ptep_get(pte_t *ptep)
>>   {
>> @@ -360,7 +365,10 @@ static inline pmd_t pmdp_huge_get_and_clear(struct mm_struct *mm,
>>   					    pmd_t *pmdp)
>>   {
>>   	pmd_t pmd = *pmdp;
>> +
>>   	pmd_clear(pmdp);
>> +	page_table_check_pmd_clear(mm, address, pmd);
>> +
>>   	return pmd;
>>   }
>>   #endif /* __HAVE_ARCH_PMDP_HUGE_GET_AND_CLEAR */
>> @@ -372,6 +380,8 @@ static inline pud_t pudp_huge_get_and_clear(struct mm_struct *mm,
>>   	pud_t pud = *pudp;
>>   
>>   	pud_clear(pudp);
>> +	page_table_check_pud_clear(mm, address, pud);
>> +
>>   	return pud;
>>   }
>>   #endif /* __HAVE_ARCH_PUDP_HUGE_GET_AND_CLEAR */
> .