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

[Anshuman Khandual <anshuman.khandual@arm.com>]

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.

> 
> 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.

> -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.

> +}
> +#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 */