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Message-ID: <8ce3eb46-2b18-e268-1013-d713c4c8f90b@huawei.com>
Date:   Mon, 25 Apr 2022 19:34:14 +0800
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Subject: Re: [PATCH -next v5 3/5] mm: page_table_check: add hooks to public
 helpers
To:     Anshuman Khandual <anshuman.khandual@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Pasha Tatashin <pasha.tatashin@soleen.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>
CC:     <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-riscv@lists.infradead.org>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Guohanjun <guohanjun@huawei.com>
References: <20220421082042.1167967-1-tongtiangen@huawei.com>
 <20220421082042.1167967-4-tongtiangen@huawei.com>
 <7fc56f41-a3c2-76be-7a20-dda392f3c4fc@arm.com>
 <eaf17cfc-880e-2181-b253-d520781c428f@huawei.com>
 <0f4de9db-1e36-b9d8-bd94-6e3ec3842940@arm.com>
From:   Tong Tiangen <tongtiangen@huawei.com>
In-Reply-To: <0f4de9db-1e36-b9d8-bd94-6e3ec3842940@arm.com>
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在 2022/4/25 13:52, Anshuman Khandual 写道:
> 
> 
> On 4/24/22 09:40, Tong Tiangen wrote:
>>
>>
>> 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.
> 
> Although there might not be a build problem as such, but should non subscribing
> platforms get their page table helpers instrumented with page table check hooks
> in the first place ? The commit message should address these questions.
> 
Add description in commit message to explain that:
Non subscription platforms will call a fallback ptc stubs when getting 
their page table helpers[1] in include/linux/pgtable.h.

[1] 
ptep_clear/ptep_get_and_clear/pmdp_huge_get_and_clear/pudp_huge_get_and_clear

Am i right? :)

Thanks,
Tong.
>>
>>>
>>>>
>>>> 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?
> 
> But other generic page table helpers already have page table check hooks
> instrumented without IS_ENABLED() checks, then why this is any different.
> 
Maybe i understand what you said, the more reasonable implement is:

static inline pte_t ptep_get_and_clear(struct mm_struct *mm, unsigned 
long address, pte_t *ptep)
  {
  	pte_t pte = *ptep;
  	pte_clear(mm, address, ptep);
	page_table_check_pte_clear(mm, address, pte);
  	return pte;
  }

static inline void ptep_clear(struct mm_struct *mm, unsigned long addr, 
pte_t *ptep)
{
	ptep_get_and_clear(mm, address, ptep);
}

>>
>> 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 */
>>> .
> .