Re: [PATCH v4 1/3] KVM: x86: Provide per VM capability for disabling PMU virtualization

[Like Xu <like.xu.linux@gmail.com>]

On 22/1/2022 6:29 am, David Dunn wrote:
> KVM_CAP_PMU_DISABLE is used to disable PMU virtualization on individual
> x86 VMs.  PMU configuration must be done prior to creating VCPUs.
> 
> To enable future extension, KVM_CAP_PMU_CAPABILITY reports available
> settings via bitmask when queried via check_extension.
> 
> For VMs that have PMU virtualization disabled, CPUID leaf 0xA will be
> cleared to notify guests.
> 
> Signed-off-by: David Dunn <daviddunn@google.com>
> ---
>   Documentation/virt/kvm/api.rst  | 21 +++++++++++++++++++++
>   arch/x86/include/asm/kvm_host.h |  1 +
>   arch/x86/kvm/cpuid.c            |  8 ++++++++
>   arch/x86/kvm/svm/pmu.c          |  2 +-
>   arch/x86/kvm/vmx/pmu_intel.c    |  2 +-
>   arch/x86/kvm/x86.c              | 12 ++++++++++++
>   include/uapi/linux/kvm.h        |  4 ++++
>   tools/include/uapi/linux/kvm.h  |  4 ++++
>   8 files changed, 52 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index bb8cfddbb22d..375d35e8ac47 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -7559,3 +7559,24 @@ The argument to KVM_ENABLE_CAP is also a bitmask, and must be a subset
>   of the result of KVM_CHECK_EXTENSION.  KVM will forward to userspace
>   the hypercalls whose corresponding bit is in the argument, and return
>   ENOSYS for the others.
> +
> +8.35 KVM_CAP_PMU_CAPABILITY
> +---------------------------
> +
> +:Capability KVM_CAP_PMU_CAPABILITY
> +:Architectures: x86
> +:Type: vm

:Parameters: args[0] defines ....
:Returns: 0 on success, -EINVAL when args[0] contains invalid bits

> +
> +This capability alters PMU virtualization in KVM.
> +
> +Calling KVM_CHECK_EXTENSION for this capability returns a bitmask of
> +PMU virtualization capabilities that can be adjusted on a VM.
> +
> +The argument to KVM_ENABLE_CAP is also a bitmask and selects specific
> +PMU virtualization capabilities to be applied to the VM.  This can
> +only be invoked on a VM prior to the creation of VCPUs.
> +
> +At this time, KVM_CAP_PMU_DISABLE is the only capability.  Setting
> +this capability will disable PMU virtualization for that VM.  When
> +PMU virtualization is disabled, CPUID leaf 0xA will always be cleared
> +to properly inform Intel guests.

Valid bits in args[0] are::

   #define KVM_CAP_PMU_DISABLE      (1 << 0)


> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 682ad02a4e58..5cdcd4a7671b 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1232,6 +1232,7 @@ struct kvm_arch {
>   	hpa_t	hv_root_tdp;
>   	spinlock_t hv_root_tdp_lock;
>   #endif
> +	bool enable_pmu;
>   };
>   
>   struct kvm_vm_stat {
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 3902c28fb6cb..a91c4a00c913 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -217,6 +217,14 @@ static void __kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu, struct kvm_cpuid_e
>   		cpuid_entry_change(best, X86_FEATURE_OSPKE,
>   				   kvm_read_cr4_bits(vcpu, X86_CR4_PKE));
>   
> +	best = cpuid_entry2_find(entries, nent, 0xA, 0);
> +	if (best && !vcpu->kvm->arch.enable_pmu) {
> +		best->eax = 0;
> +		best->ebx = 0;
> +		best->ecx = 0;
> +		best->edx = 0;
> +	}

Sorry, I don't think we should do this stuff for the buggy user space.

For others, Reviewed-by: Like Xu <likexu@tencent.com>

> +
>   	best = cpuid_entry2_find(entries, nent, 0xD, 0);
>   	if (best)
>   		best->ebx = xstate_required_size(vcpu->arch.xcr0, false);
> diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
> index 5aa45f13b16d..d4de52409335 100644
> --- a/arch/x86/kvm/svm/pmu.c
> +++ b/arch/x86/kvm/svm/pmu.c
> @@ -101,7 +101,7 @@ static inline struct kvm_pmc *get_gp_pmc_amd(struct kvm_pmu *pmu, u32 msr,
>   {
>   	struct kvm_vcpu *vcpu = pmu_to_vcpu(pmu);
>   
> -	if (!enable_pmu)
> +	if (!vcpu->kvm->arch.enable_pmu)
>   		return NULL;
>   
>   	switch (msr) {
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index 466d18fc0c5d..2c5868d77268 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -487,7 +487,7 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
>   	pmu->reserved_bits = 0xffffffff00200000ull;
>   
>   	entry = kvm_find_cpuid_entry(vcpu, 0xa, 0);
> -	if (!entry || !enable_pmu)
> +	if (!entry || !vcpu->kvm->arch.enable_pmu)
>   		return;
>   	eax.full = entry->eax;
>   	edx.full = entry->edx;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 55518b7d3b96..a033f019a3f0 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4326,6 +4326,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   		if (r < sizeof(struct kvm_xsave))
>   			r = sizeof(struct kvm_xsave);
>   		break;
> +	case KVM_CAP_PMU_CAPABILITY:
> +		r = enable_pmu ? KVM_CAP_PMU_MASK : 0;
> +		break;
>   	}
>   	default:
>   		break;
> @@ -5937,6 +5940,14 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>   		kvm->arch.exit_on_emulation_error = cap->args[0];
>   		r = 0;
>   		break;
> +	case KVM_CAP_PMU_CAPABILITY:
> +		r = -EINVAL;
> +		if (!enable_pmu || kvm->created_vcpus > 0 ||
> +		    cap->args[0] & ~KVM_CAP_PMU_MASK)
> +			break;
> +		kvm->arch.enable_pmu = !(cap->args[0] & KVM_CAP_PMU_DISABLE);
> +		r = 0;
> +		break;
>   	default:
>   		r = -EINVAL;
>   		break;
> @@ -11562,6 +11573,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>   	raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);
>   
>   	kvm->arch.guest_can_read_msr_platform_info = true;
> +	kvm->arch.enable_pmu = enable_pmu;
>   
>   #if IS_ENABLED(CONFIG_HYPERV)
>   	spin_lock_init(&kvm->arch.hv_root_tdp_lock);
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 9563d294f181..1c5e6e172817 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1133,6 +1133,7 @@ struct kvm_ppc_resize_hpt {
>   #define KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM 206
>   #define KVM_CAP_VM_GPA_BITS 207
>   #define KVM_CAP_XSAVE2 208
> +#define KVM_CAP_PMU_CAPABILITY 209
>   
>   #ifdef KVM_CAP_IRQ_ROUTING
>   
> @@ -1972,6 +1973,9 @@ struct kvm_dirty_gfn {
>   #define KVM_BUS_LOCK_DETECTION_OFF             (1 << 0)
>   #define KVM_BUS_LOCK_DETECTION_EXIT            (1 << 1)
>   
> +#define KVM_CAP_PMU_DISABLE                    (1 << 0)
> +#define KVM_CAP_PMU_MASK                       (KVM_CAP_PMU_DISABLE)
> +
>   /**
>    * struct kvm_stats_header - Header of per vm/vcpu binary statistics data.
>    * @flags: Some extra information for header, always 0 for now.
> diff --git a/tools/include/uapi/linux/kvm.h b/tools/include/uapi/linux/kvm.h
> index 9563d294f181..a361cf6e8604 100644
> --- a/tools/include/uapi/linux/kvm.h
> +++ b/tools/include/uapi/linux/kvm.h
> @@ -1133,6 +1133,7 @@ struct kvm_ppc_resize_hpt {
>   #define KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM 206
>   #define KVM_CAP_VM_GPA_BITS 207
>   #define KVM_CAP_XSAVE2 208
> +#define KVM_CAP_PMU_CAPABILITY 209
>   
>   #ifdef KVM_CAP_IRQ_ROUTING
>   
> @@ -1972,6 +1973,9 @@ struct kvm_dirty_gfn {
>   #define KVM_BUS_LOCK_DETECTION_OFF             (1 << 0)
>   #define KVM_BUS_LOCK_DETECTION_EXIT            (1 << 1)
>   
> +#define KVM_CAP_PMU_DISABLE                    (1 << 0)
> +#define KVM_CAP_PMU_MASK                       (KVM_PMU_CONFIG_DISABLE)
> +
>   /**
>    * struct kvm_stats_header - Header of per vm/vcpu binary statistics data.
>    * @flags: Some extra information for header, always 0 for now.