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(p200300cbc706fb00f5c324b23d039d52.dip0.t-ipconnect.de. [2003:cb:c706:fb00:f5c3:24b2:3d03:9d52]) by smtp.gmail.com with ESMTPSA id j6-20020a05600c190600b003a31b79dc0esm26070221wmq.1.2022.08.05.11.06.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 05 Aug 2022 11:06:05 -0700 (PDT) Message-ID: Date: Fri, 5 Aug 2022 20:06:03 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v7 01/14] mm: Add F_SEAL_AUTO_ALLOCATE seal to memfd Content-Language: en-US To: Paolo Bonzini , Chao Peng , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-doc@vger.kernel.org, qemu-devel@nongnu.org, linux-kselftest@vger.kernel.org Cc: Jonathan Corbet , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H . Peter Anvin" , Hugh Dickins , Jeff Layton , "J . Bruce Fields" , Andrew Morton , Shuah Khan , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vlastimil Babka , Vishal Annapurve , Yu Zhang , "Kirill A . Shutemov" , luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com, ak@linux.intel.com, aarcange@redhat.com, ddutile@redhat.com, dhildenb@redhat.com, Quentin Perret , Michael Roth , mhocko@suse.com, Muchun Song References: <20220706082016.2603916-1-chao.p.peng@linux.intel.com> <20220706082016.2603916-2-chao.p.peng@linux.intel.com> <472207cf-ff71-563b-7b66-0c7bea9ea8ad@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <472207cf-ff71-563b-7b66-0c7bea9ea8ad@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On 05.08.22 19:55, Paolo Bonzini wrote: > On 7/21/22 11:44, David Hildenbrand wrote: >> >> Also, I*think* you can place pages via userfaultfd into shmem. Not >> sure if that would count "auto alloc", but it would certainly bypass >> fallocate(). > > Yeah, userfaultfd_register would probably have to forbid this for > F_SEAL_AUTO_ALLOCATE vmas. Maybe the memfile_node can be reused for > this, adding a new MEMFILE_F_NO_AUTO_ALLOCATE flags? Then > userfault_register would do something like > memfile_node_get_flags(vma->vm_file) and check the result. An alternative is to simply have the shmem allocation fail in a similar way. Maybe it does already, I haven't checked (don't think so). -- Thanks, David / dhildenb