linux-kernel - Re: [PATCH -next v2 2/4] mm: page_table

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Date:   Wed, 23 Mar 2022 22:12:02 -0400
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     Tong Tiangen <tongtiangen@...wei.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH -next v2 2/4] mm: page_table_check: add hooks to public helpers

On Wed, Mar 23, 2022 at 10:07 PM Tong Tiangen <tongtiangen@...wei.com> wrote:
>
>
>
> 在 2022/3/24 1:42, Pasha Tatashin 写道:
> > On Tue, Mar 22, 2022 at 10:25 AM Tong Tiangen <tongtiangen@...wei.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@...wei.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?

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