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AFNElJ8kfJPBTlIfWZg6O5KL0Pr5vNj1LTOcxQZJ1Cqwhsj5QMcDY2fw1pwdhesnX0DoHGdwXms=@vger.kernel.org X-Gm-Message-State: AOJu0YzHEaB/TEv+6kyE940srRhOoWoalBl+zsE/gqWK9Wfjz5U/tYyZ 5U5MjohgA7axYgw2EMcVshBbzuC+NkgjehOkp2SdJ1Lf6EaRXn9BuERIh9ZbdtiDwuptwj+puVe jOhXB0A== X-Received: from pgar3.prod.google.com ([2002:a05:6a02:2e83:b0:c80:1ab9:b111]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:a106:b0:398:787c:d2e4 with SMTP id adf61e73a8af0-3aa5a8fdfdamr10252140637.17.1778184706829; Thu, 07 May 2026 13:11:46 -0700 (PDT) Date: Thu, 7 May 2026 13:11:46 -0700 In-Reply-To: <20260507142402.2175933-1-vannapurve@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260507142402.2175933-1-vannapurve@google.com> Message-ID: Subject: Re: [PATCH v3 1/1] KVM: x86: Introduce has_protected_pmu state for TDX VMs From: Sean Christopherson To: Vishal Annapurve Cc: pbonzini@redhat.com, dave.hansen@linux.intel.com, rick.p.edgecombe@intel.com, dapeng1.mi@linux.intel.com, mizhang@google.com, kai.huang@intel.com, jmattson@google.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Thu, May 07, 2026, Vishal Annapurve wrote: > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 0a1b63c63d1a..99a383455d46 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -6910,7 +6910,8 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, > break; > > mutex_lock(&kvm->lock); > - if (!kvm->created_vcpus && !kvm->arch.created_mediated_pmu) { > + if (!kvm->created_vcpus && !kvm->arch.created_mediated_pmu && > + !kvm->arch.has_protected_pmu) { An offlist Sashiko review pointed out that this will prevent doing KVM_PMU_CAP_DISABLE on a TDX VM, which could prove problematic if userspace is already explicitly disabling vPMU support for TDX. I was thinking that wouldn't be a problem since KVM already disallows KVM_PMU_CAP_DISABLE if enable_pmu=false, but in that case KVM doesn't advertise KVM_CAP_PMU_VALID_MASK: r = enable_pmu ? KVM_CAP_PMU_VALID_MASK : 0; And unless I'm misreading QEMU code, this will indeed be a problem. Argh. I was going to suggest something sightly fancier, but we rather stupidly didn't provide a flag for ENABLE, and so we can't feed has_protected_pmu into the valid mask. Lame. The other super minor detail is that kvm->arch.has_protected_pmu isn't guarded by kvm->lock, and I really hope we never get to that point (e.g. for SNP). So instead of disallowing KVM_CAP_PMU_CAPABILITY entirely, this? diff --git arch/x86/kvm/x86.c arch/x86/kvm/x86.c index dc69b8cebe0b..b833a2596430 100644 --- arch/x86/kvm/x86.c +++ arch/x86/kvm/x86.c @@ -6911,6 +6911,13 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, if (!enable_pmu || (cap->args[0] & ~KVM_CAP_PMU_VALID_MASK)) break; + if (kvm->arch.has_protected_pmu) { + WARN_ON_ONCE(kvm->arch.enable_pmu); + if (cap->args[0] == KVM_PMU_CAP_DISABLE) + r = 0; + break; + } + mutex_lock(&kvm->lock); if (!kvm->created_vcpus && !kvm->arch.created_mediated_pmu) { kvm->arch.enable_pmu = !(cap->args[0] & KVM_PMU_CAP_DISABLE); > kvm->arch.enable_pmu = !(cap->args[0] & KVM_PMU_CAP_DISABLE); > r = 0; > } > @@ -13375,7 +13376,10 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) > kvm->arch.default_tsc_khz = max_tsc_khz ? : tsc_khz; > kvm->arch.apic_bus_cycle_ns = APIC_BUS_CYCLE_NS_DEFAULT; > kvm->arch.guest_can_read_msr_platform_info = true; > - kvm->arch.enable_pmu = enable_pmu; > + if (kvm->arch.has_protected_pmu) > + kvm->arch.enable_pmu = false; > + else > + kvm->arch.enable_pmu = enable_pmu; > > #if IS_ENABLED(CONFIG_HYPERV) > spin_lock_init(&kvm->arch.hv_root_tdp_lock); > -- > 2.54.0.563.g4f69b47b94-goog >