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b=X97NYhOkX7I5225IniZPUTynTMXK2eRDsX0AxxEptwujehpTEDAI9lQY0FzAPY4Ij7 HeWSMRsCebZ/e31GAUVuIMhRqobEUXLYvFfjF4G+0qbE6Rqu0hkz/NIbekJyHVPsuYIy 68lIklKazfzbTFYp4R9b7hbjCb7QqPTJ/p+TyYoFfMTcWwIYJwIX73qcI6XLtxbY0ySz D3Bq5fWUykSAwIo0AX3+AiQ2OpLgSs4CBso/bANQ/GwDUI7ZHBLNhk1aBbfW6gH1W9Vc dCzpMFzb9IAckPdPMc8lxa/eu+po7jbYycAIAg25EgJHCBfTeOKtdlSrv1IiqzPVQrns j0RA== X-Forwarded-Encrypted: i=1; AHgh+Rrlz9TOmHGwqWPseL9ts2yVwoUWgE3YzGF3NmG2y2Pn3IHAyvtlZMHTu17q1L1voJWFIn6wn7mOkQ==@kvack.org X-Gm-Message-State: AOJu0Yx6DqoOPLYSn6pMLSssbuHUuUnuPJVGHPrJZQzRZQ97wuNqsStr yEHTVhPf8it7aCscmJyI+7og1Wx7ol+GvupcpddnJd8qtXlJU4YHmr+gFBTDxq33C9tRhIkpZez rYo83LQ== X-Received: from pglr26.prod.google.com ([2002:a63:515a:0:b0:c79:65ab:b3b4]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:430a:b0:3c3:9c4e:de3a with SMTP id adf61e73a8af0-3cc71989601mr7356121637.6.1786719899335; Fri, 14 Aug 2026 08:04:59 -0700 (PDT) Date: Fri, 14 Aug 2026 08:04:58 -0700 In-Reply-To: Mime-Version: 1.0 References: <20260807-gmem-inplace-conversion-v10-0-2fc18ee6d3ba@google.com> <20260807-gmem-inplace-conversion-v10-12-2fc18ee6d3ba@google.com> <1ec08cd8-3072-4753-ad5e-cd34956647f8@linux.intel.com> Message-ID: Subject: Re: [PATCH v10 12/41] KVM: guest_memfd: Call arch make_shared callback for to-shared conversion From: Sean Christopherson To: Ackerley Tng Cc: Binbin Wu , aik@amd.com, andrew.jones@linux.dev, 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 , John Hubbard , Peter Xu , tarunsahu@google.com, 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, Fuad Tabba Content-Type: text/plain; charset="us-ascii" X-Rspamd-Queue-Id: 5331140002 X-Rspam-User: X-Stat-Signature: 9gf4rg8pnkyz7h4rnckbka5kejb5x1oz X-Rspamd-Server: rspam06 X-HE-Tag: 1786719901-362390 X-HE-Meta: U2FsdGVkX19HtHB6XLivBEJGu+cE+8FUZtYYx/wxUizcio4CwpW+4FIBOgHTI7AN8sxLZ1reesW/IOUrSnMxk5CCsZiZeMJNDPJERyzvXofb9426CFhdKwaOES6eodRY6a5J4zSCrBrtBugn39nT77uPyTOfgSFR9+F2hHfIcF7kWircaIAvBhLdVf3CWEmxjakwAub2lhvzQmeaz6UcRif8drlWnZUy7WldMbn14nurny+eaex4QPaYK3KGYt7qiUEScg8ILw2kWOgDq9vzWaRz//nlnQH9t0R+VjO1b6XuPhzzDn9hN5DFXIqvoCWjSnet6m+K6mQldY4AreKhLOz7Ri1l3A6hXJQ3ugLciSWCwMk42I5v08m9Fw1NRLPCQkAyAKvOZ4Wp1gt7HEjpDJ5+VjWa64i16QCqtoMKU4tlrKDLVKs2rHP3pDJ4i+iK2hfHPX4oQvtrCGuFpN5mycDQUEhuY3BVvM4iTsHjsNJEQlxiw4zF18uXvryNmlQzenwXQlV/IXByMyRfiuvBtuixavgD6ysPIIpj0+xfGqtHpsK+TgF3icPn7h+48wVM/3jDrhqBugio/mnLkBj2FjpfHdmgCx6/qIKKSY00GAXF+hhf/xk7a90SBN/dfPSWhA4dPN2zutsW+mDmUhfWKTUhCJcrM94kM8dgaQHC2BqoujoJsjGRIx0CPQS4l4U6lgrZG2dQsWTy7f332C6ynrVIHZ1fhXfuGe1hKnm5HoJrjWoIyZkhc6LUuOfmEGX+6xMlvPIEeXVcYJmTZIUGIApwdKK0YCp6TNpcKeHdHP37BbAFyldxDYh3fcLzAHkP5gBmDw+mjj/9mCKSir9JZBhL4exa7T/HH2bbAMi7dFjZrflzdFu9P5e5/FhqQtsWzgLAmYTB31FLsOUBM5UJWs4GrNxm9ES5xk7WK3QrKQr8kYqkYco54gZjsTyfMryPruJqiixMO0tf6BGlUES P5MdiPUT 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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, Aug 13, 2026, Ackerley Tng wrote: > Sean Christopherson writes: > > That's why I think it's worth analyzing the cost: if it's in the > > noise, leave it alone. If it's meaningful, figure out a not-too-gross way to skip > > the entire thing if kvm_arch_gmem_make_shared() is a glorified nop in the end. > > Is noise defined relative to the entire conversion process? Would this > benchmark look like > > 1. Convert 4G to shared on TDX with CONFIG_AMD_SEV defined > 2. Convert 4G to shared on TDX without CONFIG_AMD_SEV defined > > and then compare the difference in time taken? That'd work, though I was envisioning something even simpler: use rdtsc() to count the cycles it takes to iterate over various ranges of memory. Do whatever is easiest for you though.