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AJvYcCV0rl1P04lapn6x3++aumz7kToPdfPLgXBTHo4H7NSDeN2CR/XtXuwIjIPfTlf5DJZ/6VHlyWvOcw==@kvack.org X-Gm-Message-State: AOJu0YwJZEoN4YwPitWw2iSfNDJESYQJl65cs4Mwi0HA2SM7oZviwfFu aMyEm1QH1pfx66c8YTJlxIch4T5X/nrkHSOAMgNsSGUKy02sTPbV1IV/zgVzhN4= X-Google-Smtp-Source: AGHT+IHzEyIAn5BZKdsgEF+tkgsjaGhBmdzJxEgxGtA7eOAAo7NB0TYXIZ9VX90RiBa6VatggNPMRg== X-Received: by 2002:a05:6a20:9f4e:b0:1c4:a531:bafd with SMTP id adf61e73a8af0-1cad7f8b77dmr2391092637.18.1724234617078; Wed, 21 Aug 2024 03:03:37 -0700 (PDT) Received: from [10.84.144.49] ([203.208.167.150]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7127aef610esm9588632b3a.129.2024.08.21.03.03.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 21 Aug 2024 03:03:36 -0700 (PDT) Message-ID: <83142dc8-edcf-4e47-8215-8b359a2b7156@bytedance.com> Date: Wed, 21 Aug 2024 18:03:30 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 06/14] mm: handle_pte_fault() use pte_offset_map_maywrite_nolock() Content-Language: en-US To: David Hildenbrand Cc: LEROY Christophe , "hughd@google.com" , "willy@infradead.org" , "muchun.song@linux.dev" , "vbabka@kernel.org" , "akpm@linux-foundation.org" , "rppt@kernel.org" , "vishal.moola@gmail.com" , "peterx@redhat.com" , "ryan.roberts@arm.com" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "linux-arm-kernel@lists.infradead.org" , "linuxppc-dev@lists.ozlabs.org" References: <239432a0bc56464e58a6baf3622fdc72526c8d57.1724226076.git.zhengqi.arch@bytedance.com> <6a586524-5116-4eaf-b4f3-c1aea290d7c1@cs-soprasteria.com> <4b867535-8481-4fa1-bed1-ad25a76682f0@redhat.com> <61c05197-0baa-4680-ad24-5965ba37dc35@redhat.com> From: Qi Zheng In-Reply-To: <61c05197-0baa-4680-ad24-5965ba37dc35@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: A1AB780027 X-Stat-Signature: qqb6joiarmxk6ugipxdjsnkngpubpqge X-Rspam-User: X-HE-Tag: 1724234618-548650 X-HE-Meta: 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 b/f9TojO 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2024/8/21 17:53, David Hildenbrand wrote: > On 21.08.24 11:51, Qi Zheng wrote: >> >> >> On 2024/8/21 17:41, David Hildenbrand wrote: >>> On 21.08.24 11:24, Qi Zheng wrote: >>>> >>>> >>>> On 2024/8/21 17:17, LEROY Christophe wrote: >>>>> >>>>> >>>>> Le 21/08/2024 à 10:18, Qi Zheng a écrit : >>>>>> In handle_pte_fault(), we may modify the vmf->pte after acquiring the >>>>>> vmf->ptl, so convert it to using pte_offset_map_maywrite_nolock(). >>>>>> But >>>>>> since we already do the pte_same() check, so there is no need to get >>>>>> pmdval to do pmd_same() check, just pass NULL to pmdvalp parameter. >>>>>> >>>>>> Signed-off-by: Qi Zheng >>>>>> --- >>>>>>      mm/memory.c | 9 +++++++-- >>>>>>      1 file changed, 7 insertions(+), 2 deletions(-) >>>>>> >>>>>> diff --git a/mm/memory.c b/mm/memory.c >>>>>> index 93c0c25433d02..d3378e98faf13 100644 >>>>>> --- a/mm/memory.c >>>>>> +++ b/mm/memory.c >>>>>> @@ -5504,9 +5504,14 @@ static vm_fault_t handle_pte_fault(struct >>>>>> vm_fault *vmf) >>>>>>               * pmd by anon khugepaged, since that takes mmap_lock in >>>>>> write >>>>>>               * mode; but shmem or file collapse to THP could still >>>>>> morph >>>>>>               * it into a huge pmd: just retry later if so. >>>>>> +         * >>>>>> +         * Use the maywrite version to indicate that vmf->pte >>>>>> will be >>>>>> +         * modified, but since we will use pte_same() to detect the >>>>>> +         * change of the pte entry, there is no need to get pmdval. >>>>>>               */ >>>>>> -        vmf->pte = pte_offset_map_nolock(vmf->vma->vm_mm, vmf->pmd, >>>>>> -                         vmf->address, &vmf->ptl); >>>>>> +        vmf->pte = pte_offset_map_maywrite_nolock(vmf->vma->vm_mm, >>>>>> +                              vmf->pmd, vmf->address, >>>>>> +                              NULL, &vmf->ptl); >>> >>> I think we discussed that passing NULL should be forbidden for that >>> function. >> >> Yes, but for some maywrite case, there is no need to get pmdval to >> do pmd_same() check. So I passed NULL and added a comment to >> explain this. > > I wonder if it's better to pass a dummy variable instead. One has to > think harder why that is required compared to blindly passing "NULL" :) You are afraid that subsequent caller will abuse this function, right? My initial concern was that this would add a useless local vaiable, but perhaps that is not a big deal. Both are fine for me. ;) >