linux-kernel - Re: [RFC 07/33] KVM: x86: hyper-v: Introduce KVM_CAP_HYPERV

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Message-ID: <fcd7567a1b45c6779882f696fe2fdac8c6702b3b.camel@redhat.com>
Date:   Tue, 28 Nov 2023 09:16:13 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Nicolas Saenz Julienne <nsaenz@...zon.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
        pbonzini@...hat.com, seanjc@...gle.com, vkuznets@...hat.com,
        anelkz@...zon.com, graf@...zon.com, dwmw@...zon.co.uk,
        jgowans@...zon.com, corbert@....net, kys@...rosoft.com,
        haiyangz@...rosoft.com, decui@...rosoft.com, x86@...nel.org,
        linux-doc@...r.kernel.org
Subject: Re: [RFC 07/33] KVM: x86: hyper-v: Introduce KVM_CAP_HYPERV_VSM

On Wed, 2023-11-08 at 11:17 +0000, Nicolas Saenz Julienne wrote:
> Introduce a new capability to enable Hyper-V Virtual Secure Mode (VSM)
> emulation support.
> 
> Signed-off-by: Nicolas Saenz Julienne <nsaenz@...zon.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 2 ++
>  arch/x86/kvm/hyperv.h           | 5 +++++
>  arch/x86/kvm/x86.c              | 5 +++++
>  include/uapi/linux/kvm.h        | 1 +
>  4 files changed, 13 insertions(+)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 00cd21b09f8c..7712e31b7537 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1118,6 +1118,8 @@ struct kvm_hv {
>  
>  	struct hv_partition_assist_pg *hv_pa_pg;
>  	struct kvm_hv_syndbg hv_syndbg;
> +
> +	bool hv_enable_vsm;
>  };
>  
>  struct msr_bitmap_range {
> diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
> index f83b8db72b11..2bfed69ba0db 100644
> --- a/arch/x86/kvm/hyperv.h
> +++ b/arch/x86/kvm/hyperv.h
> @@ -238,4 +238,9 @@ static inline int kvm_hv_verify_vp_assist(struct kvm_vcpu *vcpu)
>  
>  int kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu);
>  
> +static inline bool kvm_hv_vsm_enabled(struct kvm *kvm)
> +{
> +       return kvm->arch.hyperv.hv_enable_vsm;
> +}
> +
>  #endif
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 4cd3f00475c1..b0512e433032 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4485,6 +4485,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_HYPERV_CPUID:
>  	case KVM_CAP_HYPERV_ENFORCE_CPUID:
>  	case KVM_CAP_SYS_HYPERV_CPUID:
> +	case KVM_CAP_HYPERV_VSM:
>  	case KVM_CAP_PCI_SEGMENT:
>  	case KVM_CAP_DEBUGREGS:
>  	case KVM_CAP_X86_ROBUST_SINGLESTEP:
> @@ -6519,6 +6520,10 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>  		}
>  		mutex_unlock(&kvm->lock);
>  		break;
> +	case KVM_CAP_HYPERV_VSM:
> +		kvm->arch.hyperv.hv_enable_vsm = true;
> +		r = 0;
> +		break;
>  	default:
>  		r = -EINVAL;
>  		break;
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 5ce06a1eee2b..168b6ac6ebe5 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1226,6 +1226,7 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_CAP_GUEST_MEMFD 233
>  #define KVM_CAP_VM_TYPES 234
>  #define KVM_CAP_APIC_ID_GROUPS 235
> +#define KVM_CAP_HYPERV_VSM 237
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  

Do we actually need this? Can we detect if the userspace wants VSM using
guest CPUID?

Of course if we need to add a new ioctl or something it will have to be
done together with a new capability, and since we will need at least to
know a vCPU's VTL, we will probably need this capability.

Best regards,
	Maxim Levitsky