Re: [PATCH -next v6 5/6] arm64/mm: Enable ARCH_SUPPORTS_PAGE_TABLE_CHECK

From: Tong Tiangen <tongtiangen@huawei.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: 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>,
	Will Deacon <will@kernel.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>, <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>
Subject: Re: [PATCH -next v6 5/6] arm64/mm: Enable ARCH_SUPPORTS_PAGE_TABLE_CHECK
Date: Thu, 5 May 2022 14:46:51 +0800	[thread overview]
Message-ID: <3f0439c7-9c25-b83a-58dd-9c3d638b9236@huawei.com> (raw)
In-Reply-To: <YnK3U3qDhhgwaULb@arm.com>

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.