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Wed, 28 Feb 2024 10:18:47 +0800 Message-ID: Date: Wed, 28 Feb 2024 10:18:47 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird CC: , , , , , , , , , , , , , , , , Subject: Re: [Question] CoW on VM_PFNMAP vma during write fault Content-Language: en-US To: References: <20240227122814.3781907-1-mawupeng1@huawei.com> From: mawupeng In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.178.120] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpemd200001.china.huawei.com (7.185.36.224) X-Rspamd-Queue-Id: 0A817180008 X-Rspam-User: X-Stat-Signature: s8g8sikwrxuakyf7taii6xj1nbq5j9o8 X-Rspamd-Server: rspam03 X-HE-Tag: 1709086732-35816 X-HE-Meta: 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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 2024/2/28 10:10, Matthew Wilcox wrote: > On Wed, Feb 28, 2024 at 09:55:24AM +0800, 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). >> >> just a device fd with device-specify mmap which use remap_pfn_range to assign memory. > > But what meaning do you want MAP_PRIVATE of this fd to have? Does it > make sense to permit this, or should you rather just return -EINVAL if > somebody tries to mmap() with MAP_PRIVATE set? I think return -EINVAL if somebody tries to mmap() with MAP_PRIVATE and MAP_MAYWRITE is reasonable to me. Read to this pfnmap vma will not trigger fault. >