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[2003:cb:c706:fb00:f5c3:24b2:3d03:9d52]) by smtp.gmail.com with ESMTPSA id ck19-20020a5d5e93000000b0021ee65426a2sm3893063wrb.65.2022.08.05.06.28.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 05 Aug 2022 06:28:52 -0700 (PDT) Message-ID: <203c752f-9439-b5ae-056c-27b2631dcb81@redhat.com> Date: Fri, 5 Aug 2022 15:28:50 +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 05/14] mm/memfd: Introduce MFD_INACCESSIBLE flag Content-Language: en-US To: 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: Paolo Bonzini , 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> <20220706082016.2603916-6-chao.p.peng@linux.intel.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20220706082016.2603916-6-chao.p.peng@linux.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06.07.22 10:20, Chao Peng wrote: > Introduce a new memfd_create() flag indicating the content of the > created memfd is inaccessible from userspace through ordinary MMU > access (e.g., read/write/mmap). However, the file content can be > accessed via a different mechanism (e.g. KVM MMU) indirectly. > > It provides semantics required for KVM guest private memory support > that a file descriptor with this flag set is going to be used as the > source of guest memory in confidential computing environments such > as Intel TDX/AMD SEV but may not be accessible from host userspace. > > The flag can not coexist with MFD_ALLOW_SEALING, future sealing is > also impossible for a memfd created with this flag. It's kind of weird to have it that way. Why should the user have to care? It's the notifier requirement to have that, no? Why can't we handle that when register a notifier? If anything is already mapped, fail registering the notifier if the notifier has these demands. If registering succeeds, block it internally. Or what am I missing? We might not need the memfile set flag semantics eventually and would not have to expose such a flag to user space. -- Thanks, David / dhildenb