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AHgh+RqlfoBiGkj1Biu6Ho7B8q/UR19iH2Gg5gA8TsLJZdRW1LUhZqsRp2xMt37kjhccjNRIUCrA8pt1RA==@kvack.org X-Gm-Message-State: AFuF++n31vDjONFS8EaQaCgSk7gdnp0LkfWR+p8XIX0SfXCHPSqRHoGZ Q7D3uJdBNd24Ue4DHojVXqPW6lTDJ/yZlSv8hvcPWVqiUlNMWg680Zdt3jLsi5PtC+RV98s/ZSr 6nNpzaw== X-Received: from pgbd18-n1.prod.google.com ([2002:a05:6a02:64d2:10b0:cc3:28ba:e8b1]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:7284:b0:3d0:cc29:ff63 with SMTP id adf61e73a8af0-3d7ae4ed97emr13763648637.12.1788287205983; Tue, 01 Sep 2026 11:26:45 -0700 (PDT) Date: Tue, 1 Sep 2026 11:26:45 -0700 In-Reply-To: Mime-Version: 1.0 References: <20260830-gmem-inplace-conversion-v12-0-85e5fd25252a@google.com> <20260830-gmem-inplace-conversion-v12-23-85e5fd25252a@google.com> Message-ID: Subject: Re: [PATCH v12 23/45] 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, 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 , 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, Randy Dunlap , Lorenzo Stoakes , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , 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, Xiaoyao Li Content-Type: text/plain; charset="us-ascii" X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: C8F4220002 X-Stat-Signature: 3daniqa5aujk9hr7rj3tifswrbrpncgz X-Rspam-User: X-HE-Tag: 1788287207-56856 X-HE-Meta: U2FsdGVkX1/WHJfGfQzOsQ/6IBTCtY5QHTlpbzFMfYdU3tPs3MgP+LaOCajlJVQnJxwfRjz1kPYcoredO8KD02+HDV6waGvOMd83ziBn65VUzzYxLWylDfDzQoD6ky9sX75hfIRyVpMzWw8aD/4zz35nwSndox/vVXeFTh0AdJSDYF68CY1phJu23/OVltbkB58o/VLd0D0sNynbVCJMX+q/GYD7ExKe+H5OYpBGr9NMe3j8LhZArGKXfQ8qGxwvoPOX6Xcs8lTO7h13mBUHYg6nUQwrTu4s49usVFOCJ37gqP5N7yN6Z8oAEmR9ghgkjvjWd6VYYO6lF2N/M+nL7IAm5guYVfygkTMcMh0vp81nulFkXJljPUsIwKvt/QLZR/6QVDRPTBxr4edjlCXZ/Gxx1KqOMfaRXkIxdAqw0l5LouLxLyJ0L+uHyrPsNK5OJoV33NlJXILA5xJerTu9wbWkpZYAUoi+d+fjAAY50YRC2napsClI6HIehPBfwJYJND79QkxMlPuSsJB85q5/o6oUHHCGdebzKFZRi5vXwkUxXNk2TDIN1ryzs1BIQtr20krBr6N2MVaFG7oDv+tSozFGmxQhLgPbbv/0mJfZRiQS7j2snE9g9bEz7C3FOrrpaFLqrpeLW/W1UckFNRDYcuXjRiQpUwItMq64J5bKeDDtKwFMN9Ozctu5Xvej47wmIXEqcUHS/WGoNTCpOFXymkadggjub+HHVZPTqE5I87VPLG9mwYrRpuIu4nISidQkVV5piUG9jbjGF6swiYW/bqMKuSsNyXqBqnpeilcPKRERiZQVIBtafVbdWhYK3lBzaT3+pRGaeoV+jIBVwAXvU4BhrUE0plh2Gs6oUd7t9+7DTp9zld+KwHY16v/2u0P9YR/6PWKs8HLmyFCql8BLM6o5cxA0q4Ffd7CCC295n1gvNZK9v0TKqwrQaIWDoO0mSFx1Kqoimm0GYXbc7Me dTinB1Qv 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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 Tue, Sep 01, 2026, Fuad Tabba wrote: > Hi Sean, Ackerley, > > On Mon, 31 Aug 2026 at 01:25, Ackerley Tng via B4 Relay > wrote: > ... > > + kvm.gmem_in_place_conversion= > > + [KVM] Controls whether KVM enables in-place conversion > > + support for guest_memfd and tracks the private/shared > > + state of memory per guest_memfd instead of per VM. > > + > > + If enabled, KVM enables the KVM_SET_MEMORY_ATTRIBUTES2 > > + ioctl on guest_memfd file descriptors and disables the > > + legacy VM-scoped KVM_SET_MEMORY_ATTRIBUTES ioctl for > > + private memory state tracking. Only the > > + KVM_MEMORY_ATTRIBUTE_PRIVATE attribute moves to > > + per-guest_memfd tracking; other attributes remain > > + per-VM. > > + > > + This parameter toggles KVM's in-place conversion > > + capability support. Whether a VMM uses separate backends > > + or out-of-place memory management is determined by > > + userspace VMM design. > > + > > + Note, this parameter is only available when > > + CONFIG_KVM_VM_MEMORY_ATTRIBUTES=y. When > > + CONFIG_KVM_VM_MEMORY_ATTRIBUTES is not set, in-place > > + conversion is unconditionally enabled. > > + > > + Default is Y (on). > > The parameter is only settable when CONFIG_KVM_VM_MEMORY_ATTRIBUTES=y, and > in that config gmem_in_place_conversion initialises to > !IS_ENABLED(CONFIG_KVM_VM_MEMORY_ATTRIBUTES), i.e. N, not Y. Is the doc line > wrong, or is N-by-default not what was intended here? The doc is wrong. The intent is to maintain backwards compatibility with existing deployments if KVM_VM_MEMORY_ATTRIBUTES=y. > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > index 05c518c9b8078..929fd3e1a01e6 100644 > > --- a/virt/kvm/kvm_main.c > > +++ b/virt/kvm/kvm_main.c > > @@ -103,7 +103,10 @@ static bool __ro_after_init allow_unsafe_mappings; > > module_param(allow_unsafe_mappings, bool, 0444); > > > > #ifdef kvm_arch_has_private_mem > > -bool __ro_after_init gmem_in_place_conversion = false; > > +bool __ro_after_init gmem_in_place_conversion = !IS_ENABLED(CONFIG_KVM_VM_MEMORY_ATTRIBUTES); > > +#ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES > > +module_param(gmem_in_place_conversion, bool, 0444); > > +#endif > > EXPORT_SYMBOL_FOR_KVM_INTERNAL(gmem_in_place_conversion); > > #endif