Re: [PATCH v2 5/6] kvm: x86: Emulate MSR IA32_CORE_CAPABILITIES

[Xiaoyao Li <xiaoyao.li@xxxxxxxxx>]

On 2/4/2020 5:43 AM, Sean Christopherson wrote:
> On Mon, Feb 03, 2020 at 11:16:07PM +0800, Xiaoyao Li wrote:
> > Emulate MSR_IA32_CORE_CAPABILITIES in software and unconditionally
> > advertise its support to userspace. Like MSR_IA32_ARCH_CAPABILITIES, it
> > is a feature-enumerating MSR and can be fully emulated regardless of
> > hardware support. Existence of CORE_CAPABILITIES is enumerated via
> > CPUID.(EAX=7H,ECX=0):EDX[30].
> >
> > Note, support for individual features enumerated via CORE_CAPABILITIES,
> > e.g., split lock detection, will be added in future patches.
> >
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> > ---
> >   arch/x86/include/asm/kvm_host.h |  1 +
> >   arch/x86/kvm/cpuid.c            |  5 +++--
> >   arch/x86/kvm/x86.c              | 22 ++++++++++++++++++++++
> >   3 files changed, 26 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 329d01c689b7..dc231240102f 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -591,6 +591,7 @@ struct kvm_vcpu_arch {
> >   	u64 ia32_xss;
> >   	u64 microcode_version;
> >   	u64 arch_capabilities;
> > +	u64 core_capabilities;
> >   
> >   	/*
> >   	 * Paging state of the vcpu
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > index b1c469446b07..7282d04f3a6b 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -409,10 +409,11 @@ static inline void do_cpuid_7_mask(struct kvm_cpuid_entry2 *entry, int index)
> >   		    boot_cpu_has(X86_FEATURE_AMD_SSBD))
> >   			entry->edx |= F(SPEC_CTRL_SSBD);
> >   		/*
> > -		 * We emulate ARCH_CAPABILITIES in software even
> > -		 * if the host doesn't support it.
> > +		 * ARCH_CAPABILITIES and CORE_CAPABILITIES are emulated in
> > +		 * software regardless of host support.
> >   		 */
> >   		entry->edx |= F(ARCH_CAPABILITIES);
> > +		entry->edx |= F(CORE_CAPABILITIES);
> >   		break;
> >   	case 1:
> >   		entry->eax &= kvm_cpuid_7_1_eax_x86_features;
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 821b7404c0fd..a97a8f5dd1df 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -1222,6 +1222,7 @@ static const u32 emulated_msrs_all[] = {
> >   	MSR_IA32_TSC_ADJUST,
> >   	MSR_IA32_TSCDEADLINE,
> >   	MSR_IA32_ARCH_CAPABILITIES,
> > +	MSR_IA32_CORE_CAPS,
> >   	MSR_IA32_MISC_ENABLE,
> >   	MSR_IA32_MCG_STATUS,
> >   	MSR_IA32_MCG_CTL,
> > @@ -1288,6 +1289,7 @@ static const u32 msr_based_features_all[] = {
> >   	MSR_F10H_DECFG,
> >   	MSR_IA32_UCODE_REV,
> >   	MSR_IA32_ARCH_CAPABILITIES,
> > +	MSR_IA32_CORE_CAPS,
> >   };
> >   
> >   static u32 msr_based_features[ARRAY_SIZE(msr_based_features_all)];
> > @@ -1341,12 +1343,20 @@ static u64 kvm_get_arch_capabilities(void)
> >   	return data;
> >   }
> >   
> > +static u64 kvm_get_core_capabilities(void)
> > +{
> > +	return 0;
> > +}
> > +
> >   static int kvm_get_msr_feature(struct kvm_msr_entry *msr)
> >   {
> >   	switch (msr->index) {
> >   	case MSR_IA32_ARCH_CAPABILITIES:
> >   		msr->data = kvm_get_arch_capabilities();
> >   		break;
> > +	case MSR_IA32_CORE_CAPS:
> > +		msr->data = kvm_get_core_capabilities();
> > +		break;
> >   	case MSR_IA32_UCODE_REV:
> >   		rdmsrl_safe(msr->index, &msr->data);
> >   		break;
> > @@ -2716,6 +2726,11 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> >   			return 1;
> >   		vcpu->arch.arch_capabilities = data;
> >   		break;
> > +	case MSR_IA32_CORE_CAPS:
> > +		if (!msr_info->host_initiated)
>
> Shouldn't @data be checked against kvm_get_core_capabilities()?

Maybe it's for the case that userspace might have the ability to emulate 
SLD feature? And we usually let userspace set whatever it wants, e.g., 
ARCH_CAPABILITIES.

Anyway, I have no objection to add this check.

> > +			return 1;
> > +		vcpu->arch.core_capabilities = data;
> > +		break;
> >   	case MSR_EFER:
> >   		return set_efer(vcpu, msr_info);
> >   	case MSR_K7_HWCR:
> > @@ -3044,6 +3059,12 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> >   			return 1;
> >   		msr_info->data = vcpu->arch.arch_capabilities;
> >   		break;
> > +	case MSR_IA32_CORE_CAPS:
> > +		if (!msr_info->host_initiated &&
> > +		    !guest_cpuid_has(vcpu, X86_FEATURE_CORE_CAPABILITIES))
> > +			return 1;
> > +		msr_info->data = vcpu->arch.core_capabilities;
> > +		break;
> >   	case MSR_IA32_POWER_CTL:
> >   		msr_info->data = vcpu->arch.msr_ia32_power_ctl;
> >   		break;
> > @@ -9288,6 +9309,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
> >   		goto free_guest_fpu;
> >   
> >   	vcpu->arch.arch_capabilities = kvm_get_arch_capabilities();
> > +	vcpu->arch.core_capabilities = kvm_get_core_capabilities();
> >   	vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT;
> >   	kvm_vcpu_mtrr_init(vcpu);
> >   	vcpu_load(vcpu);
> > --
> > 2.23.0