Messages in this thread |  | | From | Vishal Annapurve <> | | Date | Wed, 6 May 2026 16:39:25 -0700 | | Subject | Re: [PATCH 2/2] KVM: TDX: Disable pmu virtualization for TDX VMs |
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On Wed, May 6, 2026 at 4:03 PM Sean Christopherson <seanjc@google.com> wrote: > > On Tue, May 05, 2026, FirstName LastName wrote: > > From: Vishal Annapurve <vannapurve@google.com> > > > > TDX module virtualizes PMU for TDX VMs[1]. Host has following > > toggles to control the PMU functionality exposed to TDX VMs: > > 1) Configure TD_PARAMS to allow guests to use performance monitoring. > > 2) Restrict the TD to a subset of the PEBS counters if supported. > > 3) Limit the TD to setup a certain perfmon events using basic/enhanced > > event filtering. > > > > KVM will need to be enlightened to support these toggles. Explicitly > > disable PMU virtualization for TDX VMs by default until such a support lands. > > > > [1] Section 15.2: https://cdrdv2.intel.com/v1/dl/getContent/733575 > > > > Suggested-by: Sean Christopherson <seanjc@google.com> > > Signed-off-by: Vishal Annapurve <vannapurve@google.com> > > --- > > arch/x86/kvm/vmx/tdx.c | 6 ++++++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c > > index 1e47c194af53..01498c25942d 100644 > > --- a/arch/x86/kvm/vmx/tdx.c > > +++ b/arch/x86/kvm/vmx/tdx.c > > @@ -638,6 +638,12 @@ int tdx_vm_init(struct kvm *kvm) > > kvm->arch.has_private_mem = true; > > kvm->arch.disabled_quirks |= KVM_X86_QUIRK_IGNORE_GUEST_PAT; > > > > + /* > > + * PMU support is provide by the TDX-Module (if enabled for the VM). > > + * From KVM's perspective, the VM doesn't have a virtual PMU. > > + */ > > + kvm->arch.enable_pmu = false; > > Gah, I forgot that KVM_CAP_PMU_CAPABILITY allows re-enabling PMU support (which > is really quite annoying). Unless we want to risk breaking userspace, the best > idea I can come up with is to add a has_protected_pmu flag, and then disallow > KVM_CAP_PMU_CAPABILITY. > > The question then becomes, do we keep patch 1 and also clear enable_pmu in tdx.c, > or do we keep the ordering and have kvm_arch_init_vm() consume has_protected_pmu? > Neither one is particularly awesome :-/
I am inclined to send the v2 with the latter option i.e. keep the ordering the same and have kvm_arch_init_vm() consume has_protected_pmu. Let's see how that goes.
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index c470e40a00aa..8371dcaaed1a 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -1422,6 +1422,7 @@ struct kvm_arch { > bool has_private_mem; > bool has_protected_state; > bool has_protected_eoi; > + bool has_protected_pmu; > bool pre_fault_allowed; > struct hlist_head *mmu_page_hash; > struct list_head active_mmu_pages; > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c > index 04ce321ebdf3..3ba295bd44f8 100644 > --- a/arch/x86/kvm/vmx/tdx.c > +++ b/arch/x86/kvm/vmx/tdx.c > @@ -635,6 +635,7 @@ int tdx_vm_init(struct kvm *kvm) > * i.e. all EOIs are accelerated and never trigger exits. > */ > kvm->arch.has_protected_eoi = true; > + kvm->arch.has_protected_pmu = true; > kvm->arch.has_private_mem = true; > kvm->arch.disabled_quirks |= KVM_X86_QUIRK_IGNORE_GUEST_PAT; > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 0a1b63c63d1a..57d78255c80c 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) { > kvm->arch.enable_pmu = !(cap->args[0] & KVM_PMU_CAP_DISABLE); > r = 0; > }
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