Re: [PATCH v6 3/5] KVM: VMX: Emulate MSR_IA32_ARCH_CAPABILITIES

[Darren Kenny <darren.kenny@oracle.com>]

On Thu, Feb 01, 2018 at 10:59:44PM +0100, KarimAllah Ahmed wrote:
>Intel processors 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>
>Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
>Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
>Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

Reviewed-by: Darren Kenny <darren.kenny@oracle.com>

>---
> 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 263eb1f..b13314a 100644
>--- a/arch/x86/kvm/vmx.c
>+++ b/arch/x86/kvm/vmx.c
>@@ -593,6 +593,8 @@ struct vcpu_vmx {
> 	u64 		      msr_guest_kernel_gs_base;
> #endif
>
>+	u64 		      arch_capabilities;
>+
> 	u32 vm_entry_controls_shadow;
> 	u32 vm_exit_controls_shadow;
> 	u32 secondary_exec_control;
>@@ -3262,6 +3264,12 @@ 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;
>@@ -3397,6 +3405,11 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> 		vmx_disable_intercept_for_msr(vmx->vmcs01.msr_bitmap, MSR_IA32_PRED_CMD,
> 					      MSR_TYPE_W);
> 		break;
>+	case MSR_IA32_ARCH_CAPABILITIES:
>+		if (!msr_info->host_initiated)
>+			return 1;
>+		vmx->arch_capabilities = data;
>+		break;
> 	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))
>@@ -5659,6 +5672,8 @@ static void 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 c53298d..4ec142e 100644
>--- a/arch/x86/kvm/x86.c
>+++ b/arch/x86/kvm/x86.c
>@@ -1009,6 +1009,7 @@ 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
> };
>
> static unsigned num_msrs_to_save;
>-- 
>2.7.4
>