Revert "x86/svm: Set IBRS value on VM entry and exit"

CVE-2017-5753 (revert embargoed)
CVE-2017-5715 (revert embargoed)

This reverts commit d3d0f0a2.
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/x86/kvm/svm.c

@@ -138,8 +138,6 @@ struct vcpu_svm {
 
 	u64 next_rip;
 
-	u64 spec_ctrl;
-
 	u64 host_user_msrs[NR_HOST_SAVE_USER_MSRS];
 	struct {
 		u16 fs;
@@ -3054,9 +3052,6 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_VM_CR:
 		msr_info->data = svm->nested.vm_cr_msr;
 		break;
-	case MSR_IA32_SPEC_CTRL:
-		msr_info->data = svm->spec_ctrl;
-		break;
 	case MSR_IA32_UCODE_REV:
 		msr_info->data = 0x01000065;
 		break;
@@ -3193,9 +3188,6 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 	case MSR_VM_IGNNE:
 		vcpu_unimpl(vcpu, "unimplemented wrmsr: 0x%x data 0x%llx\n", ecx, data);
 		break;
-	case MSR_IA32_SPEC_CTRL:
-		svm->spec_ctrl = data;
-		break;
 	default:
 		return kvm_set_msr_common(vcpu, msr);
 	}
@@ -3834,9 +3826,6 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 
 	local_irq_enable();
 
-	if (ibrs_inuse && (svm->spec_ctrl != FEATURE_ENABLE_IBRS))
-		wrmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);
-
 	asm volatile (
 		"push %%" _ASM_BP "; \n\t"
 		"mov %c[rbx](%[svm]), %%" _ASM_BX " \n\t"
@@ -3910,12 +3899,6 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 #endif
 		);
 
-	if (ibrs_inuse) {
-		rdmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);
-		if (svm->spec_ctrl != FEATURE_ENABLE_IBRS)
-			wrmsrl(MSR_IA32_SPEC_CTRL, FEATURE_ENABLE_IBRS);
-	}
-
 #ifdef CONFIG_X86_64
 	wrmsrl(MSR_GS_BASE, svm->host.gs_base);
 #else