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[2003:cb:c733:f100:75e7:a0a4:9ac2:1abb]) by smtp.gmail.com with ESMTPSA id s16-20020a05600c45d000b00412b67388f0sm16209550wmo.6.2024.03.04.00.57.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 04 Mar 2024 00:57:39 -0800 (PST) Message-ID: <6e948123-df3a-4450-8fd3-76b9131a35a0@redhat.com> Date: Mon, 4 Mar 2024 09:57:38 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Question] CoW on VM_PFNMAP vma during write fault To: mawupeng , akpm@linux-foundation.org, khlebnikov@openvz.org, jaredeh@gmail.com, linmiaohe@huawei.com, hpa@zytor.com, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, cotte@de.ibm.com, npiggin@suse.de Cc: luto@kernel.org, peterz@infradead.org, linux-kernel@vger.kernel.org, x86@kernel.org, rdunlap@infradead.org, bhelgaas@google.com, linux-mm@kvack.org References: <20240227122814.3781907-1-mawupeng1@huawei.com> <234a5423-8d6d-444a-a27c-c772a71c9871@huawei.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: B5430180003 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: 4er45wa9oxw7ysw8s5tzfu5qn63uduo6 X-HE-Tag: 1709542967-724621 X-HE-Meta: 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 uL23w3R+ 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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 04.03.24 09:47, mawupeng wrote: > Hi Maintainers, kindly ping... > > On 2024/2/28 9:55, mawupeng wrote: >> >> >> On 2024/2/27 21:15, David Hildenbrand wrote: >>> On 27.02.24 14:00, David Hildenbrand wrote: >>>> On 27.02.24 13:28, Wupeng Ma wrote: >>>>> We find that a warn will be produced during our test, the detail log is >>>>> shown in the end. >>>>> >>>>> The core problem of this warn is that the first pfn of this pfnmap vma is >>>>> cleared during memory-failure. Digging into the source we find that this >>>>> problem can be triggered as following: >>>>> >>>>> // mmap with MAP_PRIVATE and specific fd which hook mmap >>>>> mmap(MAP_PRIVATE, fd) >>>>>     __mmap_region >>>>>       remap_pfn_range >>>>>       // set vma with pfnmap and the prot of pte is read only >>>>> >>>> >>>> Okay, so we get a MAP_PRIVATE VM_PFNMAP I assume. >>>> >>>> What fd is that exactly? Often, we disallow private mappings in the >>>> mmap() callback (for a good reason). > > We found this problem in 5.10, Commit 9f78bf330a66 ("xsk: support use vaddr as ring") Fix this > problem during supporting vaddr by remap VM_PFNMAP by VM_MIXEDMAP. But other modules which > use remap_pfn_range may still have this problem. I wrote a simple reproducer using MAP_PRIVATE of iouring queues on Friday. > > It do seems wired for private mappings, What is the good reason? I'm sure there are some use cases that require MAP_PRIVATE of such areas, and usually there is nothing wrong with that. It's just that the PAT implementation incompatible. I can submit a cleaned-up version of my patches. -- Cheers, David / dhildenb