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Commit da39556f authored by Konrad Rzeszutek Wilk's avatar Konrad Rzeszutek Wilk Committed by Thomas Gleixner
Browse files

x86/KVM/VMX: Expose SPEC_CTRL Bit(2) to the guest 



Expose the CPUID.7.EDX[31] bit to the guest, and also guard against various
combinations of SPEC_CTRL MSR values.

The handling of the MSR (to take into account the host value of SPEC_CTRL
Bit(2)) is taken care of in patch:

  KVM/SVM/VMX/x86/spectre_v2: Support the combination of guest and host IBRS

Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarIngo Molnar <mingo@kernel.org>
parent 764f3c21

arch/x86/kvm/cpuid.c

+1 −1
Original line number Diff line number Diff line
@@ -407,7 +407,7 @@ 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(SPEC_CTRL) |

		F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(SPEC_CTRL) | F(RDS) |

		F(ARCH_CAPABILITIES);



	/* all calls to cpuid_count() should be made on the same cpu */

arch/x86/kvm/vmx.c

+5 −3
Original line number Diff line number Diff line
@@ -3524,7 +3524,8 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) 
	case MSR_IA32_SPEC_CTRL:

		if (!msr_info->host_initiated &&

		    !guest_cpuid_has(vcpu, X86_FEATURE_IBRS) &&

		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))

		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) &&

		    !guest_cpuid_has(vcpu, X86_FEATURE_RDS))

			return 1;



		msr_info->data = to_vmx(vcpu)->spec_ctrl;
@@ -3643,11 +3644,12 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) 
	case MSR_IA32_SPEC_CTRL:

		if (!msr_info->host_initiated &&

		    !guest_cpuid_has(vcpu, X86_FEATURE_IBRS) &&

		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))

		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) &&

		    !guest_cpuid_has(vcpu, X86_FEATURE_RDS))

			return 1;



		/* The STIBP bit doesn't fault even if it's not advertised */

		if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP))

		if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_RDS))

			return 1;



		vmx->spec_ctrl = data;