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[34.91.112.229]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ab7b35b0d2csm564886966b.122.2025.02.11.08.29.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 Feb 2025 08:29:51 -0800 (PST) Date: Tue, 11 Feb 2025 16:29:48 +0000 From: Quentin Perret To: Fuad Tabba Cc: 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, roypat@amazon.co.uk, 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 1E5541C0009 X-Stat-Signature: 7ztugm84meuy6h4n3eem33kmwdkphprh X-HE-Tag: 1739291393-152635 X-HE-Meta: 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 a3AjscZ4 rebwzdxow9moaOuZmHWrl14B3G/AI5LUesNKOKPKGcRXbzykX2D9lKkFrTGTKH3qp5grCegPcFvNT8voylWTJfKyS/DRPZlvdgmoexgJx+AIeAwm5iP0USWc2HDkAlMe8tAgn52K2TfSDJTimiTDoMIyDkBRPE7AlphXsOZNtQcBKISWAQWhxwsvGpyl5Oga+rmEgkGb4gBOpQFfdwmEDakSZPc5qiAVTZV5K52dolQsbkmPWA8Ii5TVSPZuD50wLmKtcrfYNdKDK4xplsH12qk/WtXuy+qPSX1JAX5CgA6WRqpwdMN5Pw6qdl2yEm+otUs221qj9y1GVsC0x6mkm9hT6XPDGqlEu9wIOzOAcIcfQX62pmSf/qAKUM8xOi5KRYXw7G2Qz4Fmmj8BVO9vqKs6vYbouZPQyXVTHDsD4298Zr4kGtA67LHUB6Efxz8HOTMsFAPgU4LClIfLJKbUbGtp6gQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.001487, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tuesday 11 Feb 2025 at 16:17:25 (+0000), Fuad Tabba wrote: > Hi Quentin, > > On Tue, 11 Feb 2025 at 16:12, Quentin Perret wrote: > > > > Hi Fuad, > > > > On Tuesday 11 Feb 2025 at 12:11:25 (+0000), Fuad Tabba wrote: > > > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > > > index 117937a895da..f155d3781e08 100644 > > > --- a/include/uapi/linux/kvm.h > > > +++ b/include/uapi/linux/kvm.h > > > @@ -652,6 +652,12 @@ struct kvm_enable_cap { > > > #define KVM_VM_TYPE_ARM_IPA_SIZE_MASK 0xffULL > > > #define KVM_VM_TYPE_ARM_IPA_SIZE(x) \ > > > ((x) & KVM_VM_TYPE_ARM_IPA_SIZE_MASK) > > > + > > > +#define KVM_VM_TYPE_ARM_SW_PROTECTED (1UL << 9) > > > > FWIW, the downstream Android code has used bit 31 since forever > > for that. > > > > Although I very much believe that upstream should not care about the > > downstream mess in general, in this particular instance bit 9 really > > isn't superior in any way, and there's a bunch of existing userspace > > code that uses bit 31 today as we speak. It is very much Android's > > problem to update these userspace programs if we do go with bit 9 > > upstream, but I don't really see how that would benefit upstream > > either. > > > > So, given that there is no maintenance cost for upstream to use bit 31 > > instead of 9, I'd vote for using bit 31 and ease the landing with > > existing userspace code, unless folks are really opinionated with this > > stuff :) > > My thinking is that this bit does _not_ mean pKVM. It means an > experimental software VM that is similar to the x86 > KVM_X86_SW_PROTECTED_VM. Hence why I didn't choose bit 31. > > From Documentation/virt/kvm/api.rst (for x86): > > ''' > Note, KVM_X86_SW_PROTECTED_VM is currently only for development and testing. > Do not use KVM_X86_SW_PROTECTED_VM for "real" VMs, and especially not in > production. The behavior and effective ABI for software-protected VMs is > unstable. > ''' > > which is similar to the documentation I added here. Aha, I see, but are we going to allocate _another_ bit for protected VMs proper once they're supported? Or just update the doc for the existing bit? If the latter, then I guess this discussion can still happen :) Thanks, Quentin