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[54.240.197.234]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e3d4144f8sm1120262f8f.41.2026.10.23.10.29.12 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 23 Oct 2026 10:29:13 -0700 (PDT) From: Fred Griffoul To: Ackerley Tng Cc: Alex Williamson , Alexander Graf , Alexander Viro , Alexey Kardashevskiy , Andrew Morton , "Aneesh Kumar K.V" , Ashish Kalra , Baolin Wang , Baolu Lu , Bill Wendling , Borislav Petkov , Catalin Marinas , Christian Brauner , =?utf-8?q?Christian_K=C3=B6nig?= , Connor Williamson , Dave Hansen , Dave Jiang , David Hildenbrand , David Rientjes , David Woodhouse , Erdem Aktas , Frank van der Linden , Gregory Price , "H. Peter Anvin" , Hugh Dickins , Ingo Molnar , Jacob Pan , James Houghton , Jan Kara , Jason Gunthorpe , Jianxiong Gao , Joerg Roedel , Joey Gouly , John Starks , Jonathan Corbet , Justin Stitt , Kevin Tian , Lorenzo Stoakes , Marc Zyngier , Michael Roth , Mike Rapoport , Nathan Chancellor , Nick Desaulniers , Nicolin Chen , Oliver Upton , Paolo Bonzini , Pratyush Yadav , Randy Dunlap , Robin Murphy , Samiullah Khawaja , Sean Christopherson , Shuah Khan , Steffen Eiden , Steven Price , Suzuki K Poulose , Tarun Sahu , Thomas Gleixner , Tom Lendacky , Tycho Andersen , Vishal Annapurve , Vlastimil Babka , Will Deacon , Xu Yilun , Yan Zhao , Zenghui Yu , x86@kernel.org, Shuah Khan , Fuad Tabba , kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, llvm@lists.linux.dev Subject: Re: [PATCH RFC v2 34/50] KVM: guest_memfd: Skip checking outstanding references in PFN mode Date: Fri, 23 Oct 2026 17:29:11 +0000 Message-ID: <20261023172911.17557-1-griffoul@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261022-gmem-alternative-providers-v2-34-5dd1dc6c660a@google.com> References: <20261022-gmem-alternative-providers-v2-0-5dd1dc6c660a@google.com> <20261022-gmem-alternative-providers-v2-34-5dd1dc6c660a@google.com> X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 109AD40009 X-Stat-Signature: fa9cfs87uz9ak3w1b983kz3mhpaughmj X-Rspamd-Server: rspam01 X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=no autolearn_force=no version=4.0.1 X-HE-Tag: 1792776555-420373 X-HE-Meta: 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 HhKoRC5G 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 > + if (!kvm_gmem_is_pfn_mode(gi) && > + kvm_gmem_has_outstanding_references(inode, start, nr_pages, > err_index)) { In folio mode this check is also what guarantees that a private page belongs to the guest alone. In PFN mode there is nothing like it: if the provider also exposes the frame somewhere else, say a ring shared with a device, the VMM can still make it private. And it is not only this guest that suffers then. Whoever else uses the frame breaks: an RMP fault on SEV-SNP, a poisoned page or a machine check on TDX, a granule protection fault on CCA, or, with SW_PROTECTED, silent access to "private" memory. Only the provider knows about such frames. With an attributes output from get_pfn() (see my reply to 31/50), it could flag them as aliased, and guest_memfd would keep them shared: refuse the conversion, treat a private fault as a hole, and refuse populate. Fred