Messages in this thread Patch in this message |  | | Date | Wed, 6 May 2026 16:03:20 -0700 | | Subject | Re: [PATCH 2/2] KVM: TDX: Disable pmu virtualization for TDX VMs | | From | Sean Christopherson <> |
| |
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 :-/
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; }
|  |