Re: [PATCH v3 3/4] KVM: VMX: Emulate MSR_IA32_ARCH_CAPABILITIES

["Raj, Ashok" <ashok.raj@intel.com>]

On Tue, Jan 30, 2018 at 01:10:27AM +0100, KarimAllah Ahmed wrote:
> Future intel processors will use MSR_IA32_ARCH_CAPABILITIES MSR to indicate
> RDCL_NO (bit 0) and IBRS_ALL (bit 1). This is a read-only MSR. By default
> the contents will come directly from the hardware, but user-space can still
> override it.
> 
> [dwmw2: The bit in kvm_cpuid_7_0_edx_x86_features can be unconditional]
> 
> Cc: Asit Mallick <asit.k.mallick@intel.com>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Arjan Van De Ven <arjan.van.de.ven@intel.com>
> Cc: Tim Chen <tim.c.chen@linux.intel.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Andrea Arcangeli <aarcange@redhat.com>
> Cc: Andi Kleen <ak@linux.intel.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Jun Nakajima <jun.nakajima@intel.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Greg KH <gregkh@linuxfoundation.org>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Ashok Raj <ashok.raj@intel.com>
> Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
>  arch/x86/kvm/cpuid.c |  2 +-
>  arch/x86/kvm/vmx.c   | 15 +++++++++++++++
>  arch/x86/kvm/x86.c   |  1 +
>  3 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 033004d..1909635 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -394,7 +394,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  
>  	/* cpuid 7.0.edx*/
>  	const u32 kvm_cpuid_7_0_edx_x86_features =
> -		F(AVX512_4VNNIW) | F(AVX512_4FMAPS);
> +		F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(ARCH_CAPABILITIES);
>  
>  	/* all calls to cpuid_count() should be made on the same cpu */
>  	get_cpu();
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index ea278ce..798a00b 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -581,6 +581,8 @@ struct vcpu_vmx {
>  	u64 		      msr_host_kernel_gs_base;
>  	u64 		      msr_guest_kernel_gs_base;
>  #endif
> +	u64 		      arch_capabilities;
> +
>  	u32 vm_entry_controls_shadow;
>  	u32 vm_exit_controls_shadow;
>  	u32 secondary_exec_control;
> @@ -3224,6 +3226,12 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  	case MSR_IA32_TSC:
>  		msr_info->data = guest_read_tsc(vcpu);
>  		break;
> +	case MSR_IA32_ARCH_CAPABILITIES:
> +		if (!msr_info->host_initiated &&
> +		    !guest_cpuid_has(vcpu, X86_FEATURE_ARCH_CAPABILITIES))
> +			return 1;
> +		msr_info->data = to_vmx(vcpu)->arch_capabilities;
> +		break;
>  	case MSR_IA32_SYSENTER_CS:
>  		msr_info->data = vmcs_read32(GUEST_SYSENTER_CS);
>  		break;
> @@ -3339,6 +3347,11 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		if (data & PRED_CMD_IBPB)
>  			wrmsrl(MSR_IA32_PRED_CMD, PRED_CMD_IBPB);
>  		break;
> +	case MSR_IA32_ARCH_CAPABILITIES:
> +		if (!msr_info->host_initiated)
> +			return 1;
> +		vmx->arch_capabilities = data;
> +		break;

arch capabilities is read only. You don't need the set_msr handling for this.

>  	case MSR_IA32_CR_PAT:
>  		if (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PAT) {
>  			if (!kvm_mtrr_valid(vcpu, MSR_IA32_CR_PAT, data))
> @@ -5599,6 +5612,8 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
>  		++vmx->nmsrs;
>  	}
>  
> +	if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
> +		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, vmx->arch_capabilities);
>  
>  	vm_exit_controls_init(vmx, vmcs_config.vmexit_ctrl);
>  
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 03869eb..8e889dc 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1006,6 +1006,7 @@ static u32 msrs_to_save[] = {
>  #endif
>  	MSR_IA32_TSC, MSR_IA32_CR_PAT, MSR_VM_HSAVE_PA,
>  	MSR_IA32_FEATURE_CONTROL, MSR_IA32_BNDCFGS, MSR_TSC_AUX,
> +	MSR_IA32_ARCH_CAPABILITIES

Same here.. no need to save/restore this. 

>  };
>  
>  static unsigned num_msrs_to_save;
> -- 
> 2.7.4
>