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Wed, 6 Mar 2024 16:10:21 +0800 Subject: Re: [PATCH 3/8] mm: Return the address from page_mapped_in_vma() To: Matthew Wilcox CC: , Naoya Horiguchi , Andrew Morton References: <20240229212036.2160900-1-willy@infradead.org> <20240229212036.2160900-4-willy@infradead.org> <6a173610-9805-650b-60e7-b2a2aa504178@huawei.com> From: Miaohe Lin Message-ID: Date: Wed, 6 Mar 2024 16:10:20 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.173.135.154] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To canpemm500002.china.huawei.com (7.192.104.244) X-Rspamd-Queue-Id: E79B72001C X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 4tpn6a8a9ur1irgpmhtpk6mqo6r56j36 X-HE-Tag: 1709712625-977082 X-HE-Meta: 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 hPz780VY yCo/0HGKkpVVnF5ioxs8Tn/S/cSsVPIWIvw5Q29GH6UPa2HXP6JgsNmcXNgLftkiRLpX+IsHujxLc/lWf2zPTfKu2ps2yAVHG0FcO4OJYiCyE4mtdGC6FWAMbzwc2P7V/YjIWZomjCuzYPso0NJTIrFzVMhWTqT+LBcTIOQxwrIkdlkbWvDL1zVCNjA== 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 2024/3/6 4:09, Matthew Wilcox wrote: > On Mon, Mar 04, 2024 at 08:31:56PM +0800, Miaohe Lin wrote: >> On 2024/3/1 5:20, Matthew Wilcox (Oracle) wrote: >>> The only user of this function calls page_address_in_vma() immediately >>> after page_mapped_in_vma() calculates it and uses it to return true/false. >>> Return the address instead, allowing memory-failure to skip the call >>> to page_address_in_vma(). >> >> IIUC, this patch will change the semantic slightly. There is one corner >> case where page_mapped_in_vma() returns true but page_address_in_vma() >> returns -EFAULT if mremap is done after the check. In that case, >> SIGKILL will be sent to the user. But with this patch applied, SIGBUS >> will be sent to the user with address before doing mremap. Or am I >> miss something? > > Isn't that an example of a race that userspace can't possibly rely on? You're right. Userspace shouldn't possibly rely on it. Thanks. > It can't observe where the kernel has got to in its processing of the > fault, so it's OK if we behave if the mremap() has happened before, > during or after the two calls. > . >