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

Yang, Weijiang
2022-12-21T04:04:46Z

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);
> }