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[91.12.100.253]) by smtp.gmail.com with ESMTPSA id f14sm8395872wry.40.2021.05.18.03.06.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 May 2021 03:06:44 -0700 (PDT) Subject: Re: [PATCH v19 5/8] mm: introduce memfd_secret system call to create "secret" memory areas To: Michal Hocko , Mike Rapoport Cc: Andrew Morton , Alexander Viro , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christopher Lameter , Dan Williams , Dave Hansen , Elena Reshetova , "H. Peter Anvin" , Hagen Paul Pfeifer , Ingo Molnar , James Bottomley , Kees Cook , "Kirill A. Shutemov" , Matthew Wilcox , Matthew Garrett , Mark Rutland , Mike Rapoport , Michael Kerrisk , Palmer Dabbelt , Palmer Dabbelt , Paul Walmsley , Peter Zijlstra , "Rafael J. Wysocki" , Rick Edgecombe , Roman Gushchin , Shakeel Butt , Shuah Khan , Thomas Gleixner , Tycho Andersen , Will Deacon , Yury Norov , linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org, x86@kernel.org References: <20210513184734.29317-1-rppt@kernel.org> <20210513184734.29317-6-rppt@kernel.org> From: David Hildenbrand Organization: Red Hat Message-ID: <8e114f09-60e4-2343-1c42-1beaf540c150@redhat.com> Date: Tue, 18 May 2021 12:06:42 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18.05.21 11:59, Michal Hocko wrote: > On Sun 16-05-21 10:29:24, Mike Rapoport wrote: >> On Fri, May 14, 2021 at 11:25:43AM +0200, David Hildenbrand wrote: > [...] >>>> + if (!page) >>>> + return VM_FAULT_OOM; >>>> + >>>> + err = set_direct_map_invalid_noflush(page, 1); >>>> + if (err) { >>>> + put_page(page); >>>> + return vmf_error(err); >>> >>> Would we want to translate that to a proper VM_FAULT_..., which would most >>> probably be VM_FAULT_OOM when we fail to allocate a pagetable? >> >> That's what vmf_error does, it translates -ESOMETHING to VM_FAULT_XYZ. > > I haven't read through the rest but this has just caught my attention. > Is it really reasonable to trigger the oom killer when you cannot > invalidate the direct mapping. From a quick look at the code it is quite > unlikely to se ENOMEM from that path (it allocates small pages) but this > can become quite sublte over time. Shouldn't this simply SIGBUS if it > cannot manipulate the direct mapping regardless of the underlying reason > for that? > OTOH, it means our kernel zones are depleted, so we'd better reclaim somehow ... -- Thanks, David / dhildenb