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AFNElJ+8RmVwNKCaTC21GGs4n9rFAf9LCCL9M8ffcBniqgyJYX0s/EfFoSB1LaWOWTUDCHbDBJgFdpvNtA==@kvack.org X-Gm-Message-State: AOJu0Yysw2yzaE11uB2i9nH7H6R3vkSFpAB3pIx5ky4eAvwgeDf1tAkl rO5RLTQvVY8e0JhMMUyYv/QKhJuv1pcEcn1cPI+wse3RVw6K1mkij5P2Vy0+DhMwJJe3HFDufdJ Mu+EUuA== X-Received: from pgam26.prod.google.com ([2002:a05:6a02:2b5a:b0:c99:aff5:707d]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:6a11:b0:3bf:acb2:5d48 with SMTP id adf61e73a8af0-3bff4227b8fmr926021637.38.1782914000204; Wed, 01 Jul 2026 06:53:20 -0700 (PDT) Date: Wed, 1 Jul 2026 06:53:19 -0700 In-Reply-To: <25fdb77d-20f6-4b3a-8b3a-dbba0dc47046@intel.com> Mime-Version: 1.0 References: <20260618-gmem-inplace-conversion-v8-24-9d2959357853@google.com> <25fdb77d-20f6-4b3a-8b3a-dbba0dc47046@intel.com> Message-ID: Subject: Re: [PATCH v8 24/46] KVM: guest_memfd: Make in-place conversion the default\ From: Sean Christopherson To: Xiaoyao Li Cc: Yan Zhao , Ackerley Tng , aik@amd.com, andrew.jones@linux.dev, binbin.wu@linux.intel.com, brauner@kernel.org, chao.p.peng@linux.intel.com, david@kernel.org, jmattson@google.com, jthoughton@google.com, michael.roth@amd.com, oupton@kernel.org, pankaj.gupta@amd.com, qperret@google.com, rick.p.edgecombe@intel.com, rientjes@google.com, shivankg@amd.com, steven.price@arm.com, tabba@google.com, willy@infradead.org, wyihan@google.com, forkloop@google.com, pratyush@kernel.org, suzuki.poulose@arm.com, aneesh.kumar@kernel.org, liam@infradead.org, Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jonathan Corbet , Shuah Khan , Shuah Khan , Vishal Annapurve , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Youngjun Park , Qi Zheng , Shakeel Butt , Kiryl Shutsemau , Baoquan He , Jason Gunthorpe , Vlastimil Babka , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev Content-Type: text/plain; charset="us-ascii" X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: F2487180006 X-Stat-Signature: y67xa31oe418ue4mn8dicjqtxypuwkz4 X-HE-Tag: 1782914001-779830 X-HE-Meta: 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 NrBSZlRL 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jul 01, 2026, Xiaoyao Li wrote: > On 6/27/2026 3:06 AM, Sean Christopherson wrote: > > On Fri, Jun 26, 2026, Yan Zhao wrote: > > > My first impression of gmem_in_place_conversion=true was that it enforces gmem > > > in-place conversion. However, it actually only enforces per-gmem private/shared > > > attribute. > > > My worry was that people might think it's a kernel bug if userspace can still > > > have shared memory from other sources after they configured > > > gmem_in_place_conversion=true. > > Ah, I see where you're coming from. FWIW, truly enforcing in-place conversion > > is flat out impossible. E.g. userspace can simply replace the memslot, at which > > point the memory effectively reverts to shared. > > would something like below enforce the in-place conversion? No. > Userspace can create a memslot without gmem fd, but that memslot can only > serve as shared memory and cannot be converted. So it doesn't violate the > in-place conversion. But userspace can delete said memslot and replace it with a memslot pointing at a guest_memfd instance that was created without INIT_SHARED, at which point userspace has effected a shared=>private conversion.