linux-kernel - Re: [PATCH -next v6 5/6] arm64/mm: Enable ARCH_SUPPORTS_PAGE_TABLE

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Date:   Thu, 5 May 2022 14:46:51 +0800
From:   Tong Tiangen <tongtiangen@...wei.com>
To:     Catalin Marinas <catalin.marinas@....com>
CC:     Anshuman Khandual <anshuman.khandual@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Will Deacon <will@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-riscv@...ts.infradead.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Guohanjun <guohanjun@...wei.com>
Subject: Re: [PATCH -next v6 5/6] arm64/mm: Enable
 ARCH_SUPPORTS_PAGE_TABLE_CHECK



在 2022/5/5 1:26, Catalin Marinas 写道:
> On Tue, May 03, 2022 at 09:13:20AM +0800, Tong Tiangen wrote:
>> 在 2022/4/29 14:18, Anshuman Khandual 写道:
>>> On 4/26/22 13:40, Tong Tiangen wrote:
>>>> @@ -884,7 +928,11 @@ static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
>>>>    static inline pmd_t pmdp_huge_get_and_clear(struct mm_struct *mm,
>>>>    					    unsigned long address, pmd_t *pmdp)
>>>>    {
>>>> -	return pte_pmd(ptep_get_and_clear(mm, address, (pte_t *)pmdp));
>>>> +	pmd_t pmd = pte_pmd(__pte(xchg_relaxed(&pte_val(*(pte_t *)pmdp), 0)));
>>>
>>> Why there is any change here ? Why not just the following instead, like what you did
>>> in ptep_get_and_clear() above. The page table entry return value here just needs to
>>> be preserved for subsequent page table check helpers.
>>>
>>> 	pmd_t pmd = pte_pmd(ptep_get_and_clear(mm, address, (pte_t *)pmdp));
>>
>> The purpose of what I do here is to avoid doing page_table_check_pte_clear()
>> in ptep_get_and_clear(). there is no functional change here.
> 
> I'm fine with using xchg here but I'd go for pmd_val directly, no need
> for conversion to pte_t:
> 
> 	pmd_t pmd = __pmd(xchg_relaxed(&pmd_val(*pmdp), 0));
> 

OK, This implementation is good and avoids redundant conversion, will 
fix it next version.

Thanks,
Tong.