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[2003:cb:c707:6e00:ff02:ec7a:ded5:ec1e]) by smtp.gmail.com with ESMTPSA id u18-20020a05600c4d1200b003c21ba7d7d6sm1493548wmp.44.2023.01.05.00.47.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Jan 2023 00:47:11 -0800 (PST) Message-ID: <1f934203-5220-01f6-42d1-65cc984a0201@redhat.com> Date: Thu, 5 Jan 2023 09:47:10 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH 3/3] mm/uffd: Detect pgtable allocation failures To: Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Mike Kravetz , Muchun Song , Nadav Amit , Andrea Arcangeli , James Houghton , Axel Rasmussen , Andrew Morton References: <20230104225207.1066932-1-peterx@redhat.com> <20230104225207.1066932-4-peterx@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230104225207.1066932-4-peterx@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 9B36340008 X-Stat-Signature: o99jaig469sqouepxh55irb1n143wcfc X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1672908435-40246 X-HE-Meta: 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 xR33Pchh mbnDo+MWvOIkBq+cret/ieFNCCQ0ZyN1hvEXbw/sfcyEjXErzCaj7UVQXUQx3fGC8XF8O6nkt1uhmn/zWgpB6HGxXpMdES4cNyrxyOyu6hQvTNlCWI9PrArMMRWAXT6htjyK0+TOCor/tNinwwD8kBDmKAaUpoJHJeVUAZBBlWmcbDNYyNDWIxt4IeQARJTFFg2fCxauSJKlxBN6wKdjsV3TdjA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000017, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 04.01.23 23:52, Peter Xu wrote: > Before this patch, when there's any pgtable allocation issues happened > during change_protection(), the error will be ignored from the syscall. > For shmem, there will be an error dumped into the host dmesg. Two issues > with that: > > (1) Doing a trace dump when allocation fails is not anything close to > grace.. s/..// > > (2) The user should be notified with any kind of such error, so the user > can trap it and decide what to do next, either by retrying, or stop > the process properly, or anything else. > > For userfault users, this will change the API of UFFDIO_WRITEPROTECT when > pgtable allocation failure happened. It should not normally break anyone, > though. If it breaks, then in good ways. > > One man-page update will be on the way to introduce the new -ENOMEM for > UFFDIO_WRITEPROTECT. Not marking stable so we keep the old behavior on the > 5.19-till-now kernels. We'd now fail after already having modified some state (protected some PTEs). I assume that can already happen when protecting across multiple VMAs and is expected, right? -- Thanks, David / dhildenb