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AFNElJ8LMfOsdhwuTb8VbAkrAk7bRGAi52dHUdGLo5eOVxYikp21H8WWRzZ/VXpzHt4Hs6yOCyMvWGa1jw==@kvack.org X-Gm-Message-State: AOJu0Yz+8GrqeAjrVVfMkCQH6nu3zkhcm/VbHr8sPNXNJkcBGH9Au1NM DNZxzAHkonMReGhsGDZTQgYqUX89KjUtji2ngNaUWobqWx24GWjHvKIyAZbIrQk8scDi+BHmDPR QlzV7UQ== X-Received: from pjjj1.prod.google.com ([2002:a17:90a:601:b0:368:adeb:4994]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:2548:b0:35f:b5df:453 with SMTP id 98e67ed59e1d1-36a45630166mr2922293a91.22.1779373302968; Thu, 21 May 2026 07:21:42 -0700 (PDT) Date: Thu, 21 May 2026 07:21:42 -0700 In-Reply-To: Mime-Version: 1.0 References: <20260507-gmem-inplace-conversion-v6-0-91ab5a8b19a4@google.com> <20260507-gmem-inplace-conversion-v6-19-91ab5a8b19a4@google.com> Message-ID: Subject: Re: [PATCH v6 19/43] KVM: Let userspace disable per-VM mem attributes, enable per-gmem attributes From: Sean Christopherson To: Fuad Tabba Cc: ackerleytng@google.com, aik@amd.com, andrew.jones@linux.dev, binbin.wu@linux.intel.com, brauner@kernel.org, chao.p.peng@linux.intel.com, david@kernel.org, ira.weiny@intel.com, 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, 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 , Baoquan He , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Youngjun Park , Qi Zheng , Shakeel Butt , Kiryl Shutsemau , 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: im3h7oe6g8uh85mbcp8hfkqrh9qm9rkp X-Rspamd-Queue-Id: E2D9E4000C X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1779373304-502598 X-HE-Meta: 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 smqSVCcV 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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, May 21, 2026, Fuad Tabba wrote: > Hi Ackerley, > > On Thu, 7 May 2026 at 21:22, Ackerley Tng via B4 Relay > wrote: > > > > From: Sean Christopherson > > > > Make vm_memory_attributes a module parameter so that userspace can disable > > the use of memory attributes on the VM level. > > > > To avoid inconsistencies in the way memory attributes are tracked in KVM > > and guest_memfd, the vm_memory_attributes module_param is made > > read-only (0444). > > > > Make CONFIG_KVM_VM_MEMORY_ATTRIBUTES selectable, only for (CoCo) VM types > > that might use vm_memory_attributes. > > > > Signed-off-by: Sean Christopherson > > Signed-off-by: Ackerley Tng > > Config files always confuse me, but Sashiko might be onto something: > > https://sashiko.dev/#/patchset/20260507-gmem-inplace-conversion-v6-0-91ab5a8b19a4%40google.com?part=19 : Since this prompt does not have a default value, will it default to N : and silently drop KVM_VM_MEMORY_ATTRIBUTES during configuration updates : like make olddefconfig? : : Existing userspace VMMs that rely on the KVM_SET_MEMORY_ATTRIBUTES ioctl : for TDX or SEV VMs might fail to boot if the feature is unexpectedly : compiled out. Could a default y be used to preserve backwards : compatibility for existing configurations? > I think this partially goes back to commit 6, the one I flagged > yesterday. But also adding "default y" to KVM_VM_MEMORY_ATTRIBUTES? > The default value should at least fix this issue, but I'm not sure if > it would cause other problems... Hrm. As much as I want per-gmem attributes to be the default going forward, silently breaking existing setups isn't great. On the other hand, I'm *very* skeptical there are any SNP or TDX deployments using a distro kernel, so I'm still leaning towards forcing the issue and turning per-VM attributes off by default.