Re: [PATCH v5 10/18] kvm/x86: Emulate MSR IA32_CORE_CAPABILITY

[Paolo Bonzini <pbonzini@redhat.com>]

On 13/03/19 00:00, Fenghua Yu wrote:
> From: Xiaoyao Li <xiaoyao.li@linux.intel.com>
> 
> MSR IA32_CORE_CAPABILITY is a feature-enumerating MSR, bit 5 of which
> reports the capability of enabling detection of split locks (will be
> supported on future processors based on Tremont microarchitecture and
> later).
> 
> CPUID.(EAX=7H,ECX=0):EDX[30] will enumerate the presence of the
> IA32_CORE_CAPABILITY MSR.
> 
> Please check the latest Intel 64 and IA-32 Architectures Software
> Developer's Manual for more detailed information on the MSR and
> the split lock bit.
> 
> Since MSR_IA32_CORE_CAPABILITY is a feature-enumerating MSR, we can
> emulate it in software regardless of host's capability. What we need to
> do is to set the right value of it to report the capability of guest.
> 
> In this patch we just set the guest's core_capability as 0, because we
> haven't added support of the features it indicates to guest. It's for
> bisectability.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@linux.intel.com>
> Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
> ---
>  arch/x86/include/asm/kvm_host.h |  2 ++
>  arch/x86/kvm/cpuid.c            |  6 ++++++
>  arch/x86/kvm/x86.c              | 24 ++++++++++++++++++++++++
>  3 files changed, 32 insertions(+)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 180373360e34..2c53df4a5a2a 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -570,6 +570,7 @@ struct kvm_vcpu_arch {
>  	bool tpr_access_reporting;
>  	u64 ia32_xss;
>  	u64 microcode_version;
> +	u64 core_capability;
>  
>  	/*
>  	 * Paging state of the vcpu
> @@ -1527,6 +1528,7 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low,
>  		    unsigned long icr, int op_64_bit);
>  
>  u64 kvm_get_arch_capabilities(void);
> +u64 kvm_get_core_capability(void);
>  void kvm_define_shared_msr(unsigned index, u32 msr);
>  int kvm_set_shared_msr(unsigned index, u64 val, u64 mask);
>  
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index c07958b59f50..b7fb1822a1e5 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -505,6 +505,12 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  			 * if the host doesn't support it.
>  			 */
>  			entry->edx |= F(ARCH_CAPABILITIES);
> +			/*
> +			 * Since we emulate MSR IA32_CORE_CAPABILITY in
> +			 * software, we can always enable it for guest
> +			 * regardless of host's capability.
> +			 */
> +			entry->edx |= F(CORE_CAPABILITY);
>  		} else {
>  			entry->ebx = 0;
>  			entry->ecx = 0;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 941f932373d0..e20cbb8c2b74 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1158,6 +1158,7 @@ static u32 emulated_msrs[] = {
>  
>  	MSR_IA32_TSC_ADJUST,
>  	MSR_IA32_TSCDEADLINE,
> +	MSR_IA32_CORE_CAPABILITY,
>  	MSR_IA32_MISC_ENABLE,
>  	MSR_IA32_MCG_STATUS,
>  	MSR_IA32_MCG_CTL,
> @@ -1197,6 +1198,7 @@ static u32 msr_based_features[] = {
>  
>  	MSR_F10H_DECFG,
>  	MSR_IA32_UCODE_REV,
> +	MSR_IA32_CORE_CAPABILITY,
>  	MSR_IA32_ARCH_CAPABILITIES,
>  };
>  
> @@ -1224,9 +1226,18 @@ u64 kvm_get_arch_capabilities(void)
>  }
>  EXPORT_SYMBOL_GPL(kvm_get_arch_capabilities);
>  
> +u64 kvm_get_core_capability(void)
> +{
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(kvm_get_core_capability);
> +
>  static int kvm_get_msr_feature(struct kvm_msr_entry *msr)
>  {
>  	switch (msr->index) {
> +	case MSR_IA32_CORE_CAPABILITY:
> +		msr->data = kvm_get_core_capability();
> +		break;
>  	case MSR_IA32_ARCH_CAPABILITIES:
>  		msr->data = kvm_get_arch_capabilities();
>  		break;
> @@ -2445,6 +2456,12 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		break;
>  	case MSR_EFER:
>  		return set_efer(vcpu, data);
> +	case MSR_IA32_CORE_CAPABILITY:
> +		if (!msr_info->host_initiated)
> +			return 1;
> +
> +		vcpu->arch.core_capability = data;
> +		break;
>  	case MSR_K7_HWCR:
>  		data &= ~(u64)0x40;	/* ignore flush filter disable */
>  		data &= ~(u64)0x100;	/* ignore ignne emulation enable */
> @@ -2750,6 +2767,12 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  	case MSR_IA32_TSC:
>  		msr_info->data = kvm_scale_tsc(vcpu, rdtsc()) + vcpu->arch.tsc_offset;
>  		break;
> +	case MSR_IA32_CORE_CAPABILITY:
> +		if (!msr_info->host_initiated &&
> +		    !guest_cpuid_has(vcpu, X86_FEATURE_CORE_CAPABILITY))
> +			return 1;
> +		msr_info->data = vcpu->arch.core_capability;
> +		break;
>  	case MSR_MTRRcap:
>  	case 0x200 ... 0x2ff:
>  		return kvm_mtrr_get_msr(vcpu, msr_info->index, &msr_info->data);
> @@ -8725,6 +8748,7 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
>  
>  int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
>  {
> +	vcpu->arch.core_capability = kvm_get_core_capability();
>  	vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT;
>  	kvm_vcpu_mtrr_init(vcpu);
>  	vcpu_load(vcpu);
> 

Acked-by: Paolo Bonzini <pbonzini@redhat.com>