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Thu, 02 Nov 2023 08:48:50 -0700 (PDT) Message-ID: <6642c379-1023-4716-904f-4bbf076744c2@redhat.com> Date: Thu, 2 Nov 2023 16:48:41 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v13 16/35] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory To: David Matlack , Sean Christopherson Cc: Marc Zyngier , Oliver Upton , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexander Viro , Christian Brauner , "Matthew Wilcox (Oracle)" , Andrew Morton , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Xiaoyao Li , Xu Yilun , Chao Peng , Fuad Tabba , Jarkko Sakkinen , Anish Moorthy , Yu Zhang , Isaku Yamahata , =?UTF-8?B?TWlja2HDq2wgU2FsYcO8?= =?UTF-8?Q?n?= , Vlastimil Babka , Vishal Annapurve , Ackerley Tng , Maciej Szmigiero , David Hildenbrand , Quentin Perret , Michael Roth , Wang , Liam Merwick , Isaku Yamahata , "Kirill A . Shutemov" References: <20231027182217.3615211-1-seanjc@google.com> <20231027182217.3615211-17-seanjc@google.com> From: Paolo Bonzini Autocrypt: addr=pbonzini@redhat.com; keydata= xsEhBFRCcBIBDqDGsz4K0zZun3jh+U6Z9wNGLKQ0kSFyjN38gMqU1SfP+TUNQepFHb/Gc0E2 CxXPkIBTvYY+ZPkoTh5xF9oS1jqI8iRLzouzF8yXs3QjQIZ2SfuCxSVwlV65jotcjD2FTN04 hVopm9llFijNZpVIOGUTqzM4U55sdsCcZUluWM6x4HSOdw5F5Utxfp1wOjD/v92Lrax0hjiX DResHSt48q+8FrZzY+AUbkUS+Jm34qjswdrgsC5uxeVcLkBgWLmov2kMaMROT0YmFY6A3m1S P/kXmHDXxhe23gKb3dgwxUTpENDBGcfEzrzilWueOeUWiOcWuFOed/C3SyijBx3Av/lbCsHU Vx6pMycNTdzU1BuAroB+Y3mNEuW56Yd44jlInzG2UOwt9XjjdKkJZ1g0P9dwptwLEgTEd3Fo UdhAQyRXGYO8oROiuh+RZ1lXp6AQ4ZjoyH8WLfTLf5g1EKCTc4C1sy1vQSdzIRu3rBIjAvnC tGZADei1IExLqB3uzXKzZ1BZ+Z8hnt2og9hb7H0y8diYfEk2w3R7wEr+Ehk5NQsT2MPI2QBd wEv1/Aj1DgUHZAHzG1QN9S8wNWQ6K9DqHZTBnI1hUlkp22zCSHK/6FwUCuYp1zcAEQEAAc0j UGFvbG8gQm9uemluaSA8cGJvbnppbmlAcmVkaGF0LmNvbT7CwU0EEwECACMFAlRCcBICGwMH CwkIBwMCAQYVCAIJCgsEFgIDAQIeAQIXgAAKCRB+FRAMzTZpsbceDp9IIN6BIA0Ol7MoB15E 11kRz/ewzryFY54tQlMnd4xxfH8MTQ/mm9I482YoSwPMdcWFAKnUX6Yo30tbLiNB8hzaHeRj jx12K+ptqYbg+cevgOtbLAlL9kNgLLcsGqC2829jBCUTVeMSZDrzS97ole/YEez2qFpPnTV0 VrRWClWVfYh+JfzpXmgyhbkuwUxNFk421s4Ajp3d8nPPFUGgBG5HOxzkAm7xb1cjAuJ+oi/K CHfkuN+fLZl/u3E/fw7vvOESApLU5o0icVXeakfSz0LsygEnekDbxPnE5af/9FEkXJD5EoYG SEahaEtgNrR4qsyxyAGYgZlS70vkSSYJ+iT2rrwEiDlo31MzRo6Ba2FfHBSJ7lcYdPT7bbk9 AO3hlNMhNdUhoQv7M5HsnqZ6unvSHOKmReNaS9egAGdRN0/GPDWr9wroyJ65ZNQsHl9nXBqE AukZNr5oJO5vxrYiAuuTSd6UI/xFkjtkzltG3mw5ao2bBpk/V/YuePrJsnPFHG7NhizrxttB nTuOSCMo45pfHQ+XYd5K1+Cv/NzZFNWscm5htJ0HznY+oOsZvHTyGz3v91pn51dkRYN0otqr bQ4tlFFuVjArBZcapSIe6NV8C4cEiSTOwE0EVEJx7gEIAMeHcVzuv2bp9HlWDp6+RkZe+vtl KwAHplb/WH59j2wyG8V6i33+6MlSSJMOFnYUCCL77bucx9uImI5nX24PIlqT+zasVEEVGSRF m8dgkcJDB7Tps0IkNrUi4yof3B3shR+vMY3i3Ip0e41zKx0CvlAhMOo6otaHmcxr35sWq1Jk tLkbn3wG+fPQCVudJJECvVQ//UAthSSEklA50QtD2sBkmQ14ZryEyTHQ+E42K3j2IUmOLriF dNr9NvE1QGmGyIcbw2NIVEBOK/GWxkS5+dmxM2iD4Jdaf2nSn3jlHjEXoPwpMs0KZsgdU0pP JQzMUMwmB1wM8JxovFlPYrhNT9MAEQEAAcLBMwQYAQIACQUCVEJx7gIbDAAKCRB+FRAMzTZp sadRDqCctLmYICZu4GSnie4lKXl+HqlLanpVMOoFNnWs9oRP47MbE2wv8OaYh5pNR9VVgyhD OG0AU7oidG36OeUlrFDTfnPYYSF/mPCxHttosyt8O5kabxnIPv2URuAxDByz+iVbL+RjKaGM GDph56ZTswlx75nZVtIukqzLAQ5fa8OALSGum0cFi4ptZUOhDNz1onz61klD6z3MODi0sBZN Aj6guB2L/+2ZwElZEeRBERRd/uommlYuToAXfNRdUwrwl9gRMiA0WSyTb190zneRRDfpSK5d usXnM/O+kr3Dm+Ui+UioPf6wgbn3T0o6I5BhVhs4h4hWmIW7iNhPjX1iybXfmb1gAFfjtHfL xRUr64svXpyfJMScIQtBAm0ihWPltXkyITA92ngCmPdHa6M1hMh4RDX+Jf1fiWubzp1voAg0 JBrdmNZSQDz0iKmSrx8xkoXYfA3bgtFN8WJH2xgFL28XnqY4M6dLhJwV3z08tPSRqYFm4NMP dRsn0/7oymhneL8RthIvjDDQ5ktUjMe8LtHr70OZE/TT88qvEdhiIVUogHdo4qBrk41+gGQh b906Dudw5YhTJFU3nC6bbF2nrLlB4C/XSiH76ZvqzV0Z/cAMBo5NF/w= In-Reply-To: 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-Rspam-User: X-Stat-Signature: hnnewa7u55risx9u5qxwsq1o84wcuryw X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 49F35100013 X-HE-Tag: 1698940133-804523 X-HE-Meta: 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 GEmtFm0E 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 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: List-Subscribe: List-Unsubscribe: On 10/31/23 23:39, David Matlack wrote: >>> Maybe can you sketch out how you see this proposal being extensible to >>> using guest_memfd for shared mappings? >> For in-place conversions, e.g. pKVM, no additional guest_memfd is needed. What's >> missing there is the ability to (safely) mmap() guest_memfd, e.g. KVM needs to >> ensure there are no outstanding references when converting back to private. >> >> For TDX/SNP, assuming we don't find a performant and robust way to do in-place >> conversions, a second fd+offset pair would be needed. > Is there a way to support non-in-place conversions within a single guest_memfd? For TDX/SNP, you could have a hook from KVM_SET_MEMORY_ATTRIBUTES to guest memory. The hook would invalidate now-private parts if they have a VMA, causing a SIGSEGV/EFAULT if the host touches them. It would forbid mappings from multiple gfns to a single offset of the guest_memfd, because then the shared vs. private attribute would be tied to the offset. This should not be a problem; for example, in the case of SNP, the RMP already requires a single mapping from host physical address to guest physical address. Paolo