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References: <20240410143446.797262-1-chao.gao@intel.com> <20240410143446.797262-8-chao.gao@intel.com>
In-Reply-To: <20240410143446.797262-8-chao.gao@intel.com>
From: Jim Mattson <jmattson@google.com>
Date: Thu, 11 Apr 2024 21:22:40 -0700
Message-ID: <CALMp9eQwDJfioseiWinHN8fJSb-nrs8Eq_YezX7y+q3HEaX77Q@mail.gmail.com>
Subject: Re: [RFC PATCH v3 07/10] KVM: x86: Advertise ARCH_CAP_VIRTUAL_ENUM support
To: Chao Gao <chao.gao@intel.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, 
	daniel.sneddon@linux.intel.com, pawan.kumar.gupta@linux.intel.com, 
	Zhang Chen <chen.zhang@intel.com>, Sean Christopherson <seanjc@google.com>, 
	Paolo Bonzini <pbonzini@redhat.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, 
	Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org, 
	"H. Peter Anvin" <hpa@zytor.com>
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On Wed, Apr 10, 2024 at 8:08=E2=80=AFAM Chao Gao <chao.gao@intel.com> wrote=
:
>
> From: Zhang Chen <chen.zhang@intel.com>
>
> Bit 63 of IA32_ARCH_CAPABILITIES MSR indicates availablility of the
> VIRTUAL_ENUMERATION_MSR (index 0x50000000) which enumerates features
> like e.g., mitigation enumeration that in turn is used for the guest to
> report software mitigations it is using.
>
> Advertise ARCH_CAP_VIRTUAL_ENUM support for VMX and emulate read/write
> of the VIRTUAL_ENUMERATION_MSR. Now VIRTUAL_ENUMERATION_MSR is always 0.
>
> Signed-off-by: Zhang Chen <chen.zhang@intel.com>
> Co-developed-by: Chao Gao <chao.gao@intel.com>
> Signed-off-by: Chao Gao <chao.gao@intel.com>
> ---
>  arch/x86/kvm/svm/svm.c |  1 +
>  arch/x86/kvm/vmx/vmx.c | 19 +++++++++++++++++++
>  arch/x86/kvm/vmx/vmx.h |  2 ++
>  arch/x86/kvm/x86.c     | 16 +++++++++++++++-
>  4 files changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index d1a9f9951635..e3406971a8b7 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4288,6 +4288,7 @@ static bool svm_has_emulated_msr(struct kvm *kvm, u=
32 index)
>  {
>         switch (index) {
>         case MSR_IA32_MCG_EXT_CTL:
> +       case MSR_VIRTUAL_ENUMERATION:
>         case KVM_FIRST_EMULATED_VMX_MSR ... KVM_LAST_EMULATED_VMX_MSR:
>                 return false;
>         case MSR_IA32_SMBASE:
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index cdfcc1290d82..dcb06406fd09 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1955,6 +1955,8 @@ static inline bool is_vmx_feature_control_msr_valid=
(struct vcpu_vmx *vmx,
>         return !(msr->data & ~valid_bits);
>  }
>
> +#define VIRTUAL_ENUMERATION_VALID_BITS 0ULL
> +
>  static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
>  {
>         switch (msr->index) {
> @@ -1962,6 +1964,9 @@ static int vmx_get_msr_feature(struct kvm_msr_entry=
 *msr)
>                 if (!nested)
>                         return 1;
>                 return vmx_get_vmx_msr(&vmcs_config.nested, msr->index, &=
msr->data);
> +       case MSR_VIRTUAL_ENUMERATION:
> +               msr->data =3D VIRTUAL_ENUMERATION_VALID_BITS;
> +               return 0;
>         default:
>                 return KVM_MSR_RET_INVALID;
>         }
> @@ -2113,6 +2118,12 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, stru=
ct msr_data *msr_info)
>         case MSR_IA32_DEBUGCTLMSR:
>                 msr_info->data =3D vmcs_read64(GUEST_IA32_DEBUGCTL);
>                 break;
> +       case MSR_VIRTUAL_ENUMERATION:
> +               if (!msr_info->host_initiated &&
> +                   !(vcpu->arch.arch_capabilities & ARCH_CAP_VIRTUAL_ENU=
M))
> +                       return 1;
> +               msr_info->data =3D vmx->msr_virtual_enumeration;
> +               break;
>         default:
>         find_uret_msr:
>                 msr =3D vmx_find_uret_msr(vmx, msr_info->index);
> @@ -2457,6 +2468,14 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, stru=
ct msr_data *msr_info)
>                 }
>                 ret =3D kvm_set_msr_common(vcpu, msr_info);
>                 break;
> +       case MSR_VIRTUAL_ENUMERATION:
> +               if (!msr_info->host_initiated)
> +                       return 1;
> +               if (data & ~VIRTUAL_ENUMERATION_VALID_BITS)
> +                       return 1;
> +
> +               vmx->msr_virtual_enumeration =3D data;
> +               break;
>
>         default:
>         find_uret_msr:
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index a4dfe538e5a8..0519cf6187ac 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -294,6 +294,8 @@ struct vcpu_vmx {
>         u64                   force_spec_ctrl_mask;
>         u64                   force_spec_ctrl_value;
>
> +       u64                   msr_virtual_enumeration;
> +
>         u32                   msr_ia32_umwait_control;
>
>         /*
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9a59b5a93d0e..4721b6fe7641 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1564,6 +1564,7 @@ static const u32 emulated_msrs_all[] =3D {
>
>         MSR_K7_HWCR,
>         MSR_KVM_POLL_CONTROL,
> +       MSR_VIRTUAL_ENUMERATION,
>  };
>
>  static u32 emulated_msrs[ARRAY_SIZE(emulated_msrs_all)];
> @@ -1579,6 +1580,7 @@ static const u32 msr_based_features_all_except_vmx[=
] =3D {
>         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_except_v=
mx) +
> @@ -1621,7 +1623,8 @@ static bool kvm_is_immutable_feature_msr(u32 msr)
>          ARCH_CAP_PSCHANGE_MC_NO | ARCH_CAP_TSX_CTRL_MSR | ARCH_CAP_TAA_N=
O | \
>          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_CA=
P_GDS_NO | \
> -        ARCH_CAP_RFDS_NO | ARCH_CAP_RFDS_CLEAR | ARCH_CAP_BHI_NO)
> +        ARCH_CAP_RFDS_NO | ARCH_CAP_RFDS_CLEAR | ARCH_CAP_BHI_NO | \
> +        ARCH_CAP_VIRTUAL_ENUM)
>
>  static u64 kvm_get_arch_capabilities(void)
>  {
> @@ -1635,6 +1638,17 @@ static u64 kvm_get_arch_capabilities(void)
>          */
>         data |=3D ARCH_CAP_PSCHANGE_MC_NO;
>
> +       /*
> +        * Virtual enumeration is a paravirt feature. The only usage for =
now
> +        * is to bridge the gap caused by microarchitecture changes betwe=
en
> +        * different Intel processors. And its usage is linked to "virtua=
lize
> +        * IA32_SPEC_CTRL" which is a VMX feature. Whether AMD SVM can be=
nefit
> +        * from the same usage and how to implement it is still unclear. =
Limit
> +        * virtual enumeration to VMX.
> +        */

Virtualize IA32_SPEC_CTRL has been an SVM feature for years. See
https://lore.kernel.org/kvm/160738054169.28590.5171339079028237631.stgit@bm=
oger-ubuntu/.

> +       if (static_call(kvm_x86_has_emulated_msr)(NULL, MSR_VIRTUAL_ENUME=
RATION))
> +               data |=3D ARCH_CAP_VIRTUAL_ENUM;
> +
>         /*
>          * If we're doing cache flushes (either "always" or "cond")
>          * we will do one whenever the guest does a vmlaunch/vmresume.
> --
> 2.39.3
>
>