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AHgh+RodA4BDyV+EkelKVFqKq/GCnNgo6YM+X8dKPR5ov9WtKMnFqI31OsLnXlwyIRJU5lnmoM2vsyIlPg==@kvack.org X-Gm-Message-State: AOJu0YyfVSP4m0KTvTZKzpDG8Y57MvUMqnyHJ60Ql4E4IjU9UZnJkecU GYpBwoDaNUYGP16Axnr3i+nD01ZU6ffK1UD3Jmci5Z4rcpgECCPigtzYWvFmcshzEH25fzKw9Dl uC637Rw== X-Received: from plpn21.prod.google.com ([2002:a17:902:9695:b0:2c6:b814:535b]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:fd47:b0:2c0:b081:84b1 with SMTP id d9443c01a7336-2c7e1464d1amr26763135ad.10.1782320224855; Wed, 24 Jun 2026 09:57:04 -0700 (PDT) Date: Wed, 24 Jun 2026 09:57:04 -0700 In-Reply-To: <20260618-gmem-inplace-conversion-v8-18-9d2959357853@google.com> Mime-Version: 1.0 References: <20260618-gmem-inplace-conversion-v8-0-9d2959357853@google.com> <20260618-gmem-inplace-conversion-v8-18-9d2959357853@google.com> Message-ID: Subject: Re: [PATCH v8 18/46] KVM: guest_memfd: Handle lru_add fbatch refcounts during conversion safety check From: Sean Christopherson To: Ackerley Tng Cc: 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, yan.y.zhao@intel.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-Stat-Signature: hij3tywfodpu4qbirc1mcrb3rf1dww51 X-Rspamd-Queue-Id: 929D34000D X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1782320226-899713 X-HE-Meta: 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 q9R1p7Ig 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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 Thu, Jun 18, 2026, Ackerley Tng wrote: > When checking if a guest_memfd folio is safe for conversion, its refcount > is examined. A folio may be present in a per-CPU lru_add fbatch, which > temporarily increases its refcount. Under what circumstances does this happen, and what alternatives are there for userspace to work around the issue?