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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id p3-20020a5d68c3000000b0021ee65426a2sm11153544wrw.65.2022.08.01.01.54.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Aug 2022 01:54:55 -0700 (PDT) From: Vitaly Kuznetsov To: Paolo Bonzini , Sean Christopherson Cc: kvm@vger.kernel.org, Anirudh Rayabharam , Wanpeng Li , Jim Mattson , Maxim Levitsky , linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 09/25] KVM: VMX: nVMX: Support TSC scaling and PERF_GLOBAL_CTRL with enlightened VMCS In-Reply-To: <62ac29cb-3270-a810-bad1-3692da448016@redhat.com> References: <20220714091327.1085353-1-vkuznets@redhat.com> <20220714091327.1085353-10-vkuznets@redhat.com> <48de7ea7-fc1a-6a83-3d6f-e04d26ea2f05@redhat.com> <870d507d-a516-5601-4d21-2bfd571cf008@redhat.com> <62ac29cb-3270-a810-bad1-3692da448016@redhat.com> Date: Mon, 01 Aug 2022 10:54:54 +0200 Message-ID: <875yjc2vj5.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Paolo Bonzini writes: > On 7/29/22 00:13, Sean Christopherson wrote: >> The only flaw in this is if KVM gets handed a CPUID model that enumerates support >> for 2025 (or whenever the next update comes) but not 2022. Hmm, though if Microsoft >> defines each new "version" as a full superset, then even that theoretical bug goes >> away. I'm happy to be optimistic for once and give this a shot. I definitely like >> that it makes it easier to see the deltas between versions. > > Okay, I have queued the series but I still haven't gone through all the > comments. So this will _not_ be in the 5.21 pull request. > > The first patch also needs a bit more thought to figure out the impact > on userspace and whether we can consider syndbg niche enough to not care. (Sorry for delayed replies here, I'm back from vacation now) The first patch is not a requirement for the rest of the series, we can discuss it separately. I, however, think that we can just keep checking HV_FEATURE_DEBUG_MSRS_AVAILABLE in hv_check_msr_access() to be compatible with existing QEMUs and make QEMU expose both HV_FEATURE_DEBUG_MSRS_AVAILABLE and HV_ACCESS_DEBUG_MSRS unconditionally when syndbg feature is enabled as we know that missing HV_ACCESS_DEBUG_MSRS is just a bug. I don't think we actually need to be so picky and support VMMs which want to set 'syndbg without access to it' and 'access to syndbg without syndbg' use-cases. All-or-nothing is likely good enough. -- Vitaly