Re: [PATCH -next v2 2/4] mm: page_table_check: add hooks to public helpers

[Tong Tiangen <tongtiangen@huawei.com>]

在 2022/3/24 10:12, Pasha Tatashin 写道:
> On Wed, Mar 23, 2022 at 10:07 PM Tong Tiangen <tongtiangen@huawei.com> wrote:
>>
>>
>>
>> 在 2022/3/24 1:42, Pasha Tatashin 写道:
>>> On Tue, Mar 22, 2022 at 10:25 AM Tong Tiangen <tongtiangen@huawei.com> 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.
>>>>
>>>> Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
>>>> ---
>>>>    arch/x86/include/asm/pgtable.h | 10 ----------
>>>>    include/linux/pgtable.h        | 27 +++++++++++++++++++--------
>>>>    2 files changed, 19 insertions(+), 18 deletions(-)
>>>>
>>>> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
>>>> index 8cd6514e3052..8c85f2eabbaa 100644
>>>> --- a/arch/x86/include/asm/pgtable.h
>>>> +++ b/arch/x86/include/asm/pgtable.h
>>>> @@ -1077,16 +1077,6 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
>>>>           return pte;
>>>>    }
>>>>
>>>> -#define __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);
>>>> -}
>>>> -
>>>>    #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 f4f4077b97aa..d27fd0ed84a9 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
>>>> @@ -259,14 +260,6 @@ static inline int pmdp_clear_flush_young(struct vm_area_struct *vma,
>>>>    #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>>>>    #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,
>>>> @@ -274,10 +267,23 @@ 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)
>>>> +{
>>>> +#ifdef CONFIG_PAGE_TABLE_CHECK
>>>> +       ptep_get_and_clear(mm, addr, ptep);
>>>> +#else
>>>> +       pte_clear(mm, addr, ptep);
>>>> +#endif
>>>
>>> I have a preference to use if (IS_ENABLED(CONFIG_PAGE_TABLE_CHECK))
>>> instead of #ifdef. The end result is the same. Otherwise it looks
>>> good.
>>>
>>> Thanks,
>>> Pasha
>>> .
>>
>> I have a little hesitation when making this change , in theory, add if
>> here may affect the performance a little in some scenarios. However, the
>> impact on the whole call path should be small.
> 
> I do not think so, the compiler should optimize out IS_ENABLED() when
> not enabled, no?
> 

You are right.

https://www.kernel.org/doc/Documentation/process/coding-style.rst

The compiler will constant-fold the conditional away, and include or 
exclude the block of code just as with an #ifdef, so this will **not add 
any runtime overhead**.

Thanks :)

>>
>> I will send v3 using if (IS_ENABLED(CONFIG_PAGE_TABLE_CHECK)).
>>
>> Thanks.
>> Tong
>> .
> .