Re: [PATCH v2 1/2] KVM: x86: Introduce arch specific has_protected_pmu state

[Sean Christopherson <seanjc@google.com>]

On Thu, May 07, 2026, Vishal Annapurve wrote:
> PMU state for TDX VMs is virtualized by TDX Module [1]. Introduce
> has_protected_pmu state to track the pmu state for such scenarios. Disable
> KVM's PMU virtualization framework if pmu state is protected as
> additional enlightenment is needed within KVM to control/manage the
> visibility of PMU state to such VMs.
> 
> Additionally disallow userspace VMM to toggle PMU state using
> KVM_CAP_PMU_CAPABILITY if pmu state is protected.
> 
> [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/include/asm/kvm_host.h | 1 +
>  arch/x86/kvm/x86.c              | 8 ++++++--
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> 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/x86.c b/arch/x86/kvm/x86.c
> index 0a1b63c63d1a..4836e206f64a 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) {

Align.

>  			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;

	kvm->arch.enable_pmu = enable_pmu && !kvm->arch.has_protected_pmu;

>  #if IS_ENABLED(CONFIG_HYPERV)
>  	spin_lock_init(&kvm->arch.hv_root_tdp_lock);
> -- 
> 2.54.0.563.g4f69b47b94-goog
>