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[54.240.197.234]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a30764e9e7sm17932475e9.2.2026.10.23.10.23.47 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 23 Oct 2026 10:23:48 -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 31/50] KVM: guest_memfd: Support getting PFNs for stage 2 from providers Date: Fri, 23 Oct 2026 17:23:47 +0000 Message-ID: <20261023172347.88443-1-griffoul@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261022-gmem-alternative-providers-v2-31-5dd1dc6c660a@google.com> References: <20261022-gmem-alternative-providers-v2-0-5dd1dc6c660a@google.com> <20261022-gmem-alternative-providers-v2-31-5dd1dc6c660a@google.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit > + int (*get_pfn)(void *provider, pgoff_t index, unsigned long *pfn, > + int *max_order); Should get_pfn() also return attributes of the frame? Only the provider knows them, and every mapping of the frame has to follow them. Two examples: - Read only. A provider may lend a page that the guest can read but not write. I know you dropped this from the sample to keep things simple, but without it guest_memfd maps every frame writable, and there is no other way to make a guest_memfd page read only. - Aliased. The frame is also reachable somewhere else, e.g. a ring shared with a device. Such a frame must not become private; see my reply to 34/50. A u32 of flags, with 0 for today's behaviour, would cover both and leave room for more later. Fred