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

[Tong Tiangen]

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@xxxxxxxxxx>
> > Acked-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
> > ---
> >   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 */
> .