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[34.91.112.229]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5dece1d3738sm2872600a12.46.2025.02.14.03.13.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 14 Feb 2025 03:13:46 -0800 (PST) Date: Fri, 14 Feb 2025 11:13:41 +0000 From: Quentin Perret To: Patrick Roy Cc: Fuad Tabba , kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, seanjc@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, xiaoyao.li@intel.com, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, yu.c.zhang@linux.intel.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@google.com, ackerleytng@google.com, mail@maciej.szmigiero.name, david@redhat.com, michael.roth@amd.com, wei.w.wang@intel.com, liam.merwick@oracle.com, isaku.yamahata@gmail.com, kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com, steven.price@arm.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com, quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, catalin.marinas@arm.com, james.morse@arm.com, yuzenghui@huawei.com, oliver.upton@linux.dev, maz@kernel.org, will@kernel.org, keirf@google.com, shuah@kernel.org, hch@infradead.org, jgg@nvidia.com, rientjes@google.com, jhubbard@nvidia.com, fvdl@google.com, hughd@google.com, jthoughton@google.com Subject: Re: [PATCH v3 09/11] KVM: arm64: Introduce KVM_VM_TYPE_ARM_SW_PROTECTED machine type Message-ID: References: <20250211121128.703390-1-tabba@google.com> <20250211121128.703390-10-tabba@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tuesday 11 Feb 2025 at 17:09:20 (+0000), Quentin Perret wrote: > Hi Patrick, > > On Tuesday 11 Feb 2025 at 16:32:31 (+0000), Patrick Roy wrote: > > I was hoping that SW_PROTECTED_VM will be the VM type that something > > like Firecracker could use, e.g. an interface to guest_memfd specifically > > _without_ pKVM, as Fuad was saying. > > I had, probably incorrectly, assumed that we'd eventually want to allow > gmem for all VMs, including traditional KVM VMs that don't have anything > special. Perhaps the gmem support could be exposed via a KVM_CAP in this > case? > > Anyway, no objection to the proposed approach in this patch assuming we > will eventually have HW_PROTECTED_VM for pKVM VMs, and that _that_ can be > bit 31 :). Thinking about this a bit deeper, I am still wondering what this new SW_PROTECTED VM type is buying us? Given that SW_PROTECTED VMs accept both guest-memfd backed memslots and traditional HVA-backed memslots, we could just make normal KVM guests accept guest-memfd memslots and get the same thing? Is there any reason not to do that instead? Even though SW_PROTECTED VMs are documented as 'unstable', the reality is this is UAPI and you can bet it will end up being relied upon, so I would prefer to have a solid reason for introducing this new VM type. Cheers, Quentin