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[91.12.102.123]) by smtp.gmail.com with ESMTPSA id s63sm10249585wme.22.2021.11.22.06.57.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 22 Nov 2021 06:57:20 -0800 (PST) Message-ID: Date: Mon, 22 Nov 2021 15:57:17 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [RFC v2 PATCH 01/13] mm/shmem: Introduce F_SEAL_GUEST To: Jason Gunthorpe Cc: Chao Peng , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, qemu-devel@nongnu.org, 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 , Yu Zhang , "Kirill A . Shutemov" , luto@kernel.org, john.ji@intel.com, susie.li@intel.com, jun.nakajima@intel.com, dave.hansen@intel.com, ak@linux.intel.com References: <20211119134739.20218-1-chao.p.peng@linux.intel.com> <20211119134739.20218-2-chao.p.peng@linux.intel.com> <20211119151943.GH876299@ziepe.ca> <20211119160023.GI876299@ziepe.ca> <4efdccac-245f-eb1f-5b7f-c1044ff0103d@redhat.com> <20211122133145.GQ876299@ziepe.ca> <56c0dffc-5fc4-c337-3e85-a5c9ce619140@redhat.com> <20211122140148.GR876299@ziepe.ca> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20211122140148.GR876299@ziepe.ca> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: ffbhsc19mnrwjyhqhwkxqkbmbw8jpr3y X-Rspamd-Queue-Id: 2B79BB000806 X-Rspamd-Server: rspam07 Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="C9Wt5a/g"; spf=none (imf24.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-HE-Tag: 1637593042-467669 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: On 22.11.21 15:01, Jason Gunthorpe wrote: > On Mon, Nov 22, 2021 at 02:35:49PM +0100, David Hildenbrand wrote: >> On 22.11.21 14:31, Jason Gunthorpe wrote: >>> On Mon, Nov 22, 2021 at 10:26:12AM +0100, David Hildenbrand wrote: >>> >>>> I do wonder if we want to support sharing such memfds between processes >>>> in all cases ... we most certainly don't want to be able to share >>>> encrypted memory between VMs (I heard that the kernel has to forbid >>>> that). It would make sense in the use case you describe, though. >>> >>> If there is a F_SEAL_XX that blocks every kind of new access, who >>> cares if userspace passes the FD around or not? >> I was imagining that you actually would want to do some kind of "change >> ownership". But yeah, the intended semantics and all use cases we have >> in mind are not fully clear to me yet. If it's really "no new access" >> (side note: is "access" the right word?) then sure, we can pass the fd >> around. > > What is "ownership" in a world with kvm and iommu are reading pages > out of the same fd? In the world of encrypted memory / TDX, KVM somewhat "owns" that memory IMHO (for example, only it can migrate or swap out these pages; it's might be debatable if the TDX module or KVM actually "own" these pages ). -- Thanks, David / dhildenb