Re: [RFC PATCH 6/9] kvm/x86: Add ARCH_CAP_VIRTUAL_ENUM for guest MSR_IA32_ARCH_CAPABILITIES

["Yang, Weijiang" <weijiang.yang@intel.com>]

On 12/11/2022 12:00 AM, Zhang Chen wrote:
> Add the 63 bit in MSR_IA32_ARCH_CAPABILITIES for enable the virtual MSRs.
> Virtual MSRs can allow guests to notify VMM whether or not
> they are using specific software mitigation, allowing a VMM
> to enable there hardware control only where necessary.
> As Intel spec defination, expose virtual MSR for guest.
> Make guest have ability to check virtual MSR 0x50000000.
>
> Signed-off-by: Zhang Chen <chen.zhang@intel.com>
> ---
>   arch/x86/kvm/vmx/vmx.c | 15 +++++++++++++++
>   arch/x86/kvm/vmx/vmx.h |  1 +
>   arch/x86/kvm/x86.c     | 16 +++++++++++++++-
>   3 files changed, 31 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 407061b369b4..6ed6b743be0e 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2001,6 +2001,12 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   	case MSR_IA32_DEBUGCTLMSR:
>   		msr_info->data = vmcs_read64(GUEST_IA32_DEBUGCTL);
>   		break;
> +	case MSR_VIRTUAL_ENUMERATION:
> +		if (!msr_info->host_initiated &&
> +		    !(vcpu->arch.arch_capabilities & ARCH_CAP_VIRTUAL_ENUM))
> +			return 1;
> +		msr_info->data = vmx->msr_virtual_enumeration;
> +		break;
>   	default:
>   	find_uret_msr:
>   		msr = vmx_find_uret_msr(vmx, msr_info->index);
> @@ -2375,6 +2381,15 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   		}
>   		ret = kvm_set_msr_common(vcpu, msr_info);
>   		break;
> +	case MSR_VIRTUAL_ENUMERATION:
> +		if (msr_info->host_initiated &&
> +		    !(vcpu->arch.arch_capabilities & ARCH_CAP_VIRTUAL_ENUM))
> +			return 1;
> +		if (data & ~VIRT_ENUM_MITIGATION_CTRL_SUPPORT)
> +			return 1;
> +		vmx->msr_virtual_enumeration = data &
> +						VIRT_ENUM_MITIGATION_CTRL_SUPPORT;
> +		break;
>   
>   	default:
>   	find_uret_msr:
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index c5a41ae14237..fc873cf45f70 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -298,6 +298,7 @@ struct vcpu_vmx {
>   	 * IA32_SPEC_CTRL_MSR.
>   	 */
>   	u64		      spec_ctrl_mask;
> +	u64		      msr_virtual_enumeration;
>   	u32		      msr_ia32_umwait_control;
>   
>   	/*
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 2835bd796639..6be0a3f1281f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1532,6 +1532,8 @@ static const u32 emulated_msrs_all[] = {
>   	MSR_IA32_VMX_EPT_VPID_CAP,
>   	MSR_IA32_VMX_VMFUNC,
>   
> +	MSR_VIRTUAL_ENUMERATION,
> +
>   	MSR_K7_HWCR,
>   	MSR_KVM_POLL_CONTROL,
>   };
> @@ -1567,6 +1569,7 @@ static const u32 msr_based_features_all[] = {
>   	MSR_IA32_UCODE_REV,
>   	MSR_IA32_ARCH_CAPABILITIES,
>   	MSR_IA32_PERF_CAPABILITIES,
> +	MSR_VIRTUAL_ENUMERATION,
>   };
>   
>   static u32 msr_based_features[ARRAY_SIZE(msr_based_features_all)];
> @@ -1588,7 +1591,8 @@ static unsigned int num_msr_based_features;
>   	 ARCH_CAP_SKIP_VMENTRY_L1DFLUSH | ARCH_CAP_SSB_NO | ARCH_CAP_MDS_NO | \
>   	 ARCH_CAP_PSCHANGE_MC_NO | ARCH_CAP_TSX_CTRL_MSR | ARCH_CAP_TAA_NO | \
>   	 ARCH_CAP_SBDR_SSDP_NO | ARCH_CAP_FBSDP_NO | ARCH_CAP_PSDP_NO | \
> -	 ARCH_CAP_FB_CLEAR | ARCH_CAP_RRSBA | ARCH_CAP_PBRSB_NO)
> +	 ARCH_CAP_FB_CLEAR | ARCH_CAP_RRSBA | ARCH_CAP_PBRSB_NO | \
> +	 ARCH_CAP_VIRTUAL_ENUM)
>   
>   static u64 kvm_get_arch_capabilities(void)
>   {
> @@ -1607,6 +1611,13 @@ static u64 kvm_get_arch_capabilities(void)
>   	 */
>   	data |= ARCH_CAP_PSCHANGE_MC_NO;
>   
> +	/*
> +	 * Virtual MSRs can allow guests to notify VMM whether or not
> +	 * they are using specific software mitigation, allowing a VMM
> +	 * to enable there hardware control only where necessary.
> +	 */
> +	data |= ARCH_CAP_VIRTUAL_ENUM;


IMO, this is:  data &= ARCH_CAP_VIRTUAL_ENUM; because it requires 
platform support.


> +
>   	/*
>   	 * If we're doing cache flushes (either "always" or "cond")
>   	 * we will do one whenever the guest does a vmlaunch/vmresume.
> @@ -1657,6 +1668,9 @@ static int kvm_get_msr_feature(struct kvm_msr_entry *msr)
>   	case MSR_IA32_UCODE_REV:
>   		rdmsrl_safe(msr->index, &msr->data);
>   		break;
> +	case MSR_VIRTUAL_ENUMERATION:
> +		msr->data = VIRT_ENUM_MITIGATION_CTRL_SUPPORT;


Need to check bit 63 of host MSR_ARCH_CAPABILITIES before expose the 
feature.


> +		break;
>   	default:
>   		return static_call(kvm_x86_get_msr_feature)(msr);
>   	}