[PATCH 4/5] x86/svm: Direct access to MSR_IA32_SPEC_CTRL

[Ashok Raj]

From: Paolo Bonzini <pbonzini@xxxxxxxxxx>

Direct access to MSR_IA32_SPEC_CTRL is important
for performance.  Allow load/store of MSR_IA32_SPEC_CTRL, restore guest
IBRS on VM entry and set restore host values on VM exit.
it yet).

TBD: need to check msr's can be passed through even if feature is not
emuerated by the CPU.

[Ashok: Modified to reuse V3 spec-ctrl patches from Tim]

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Ashok Raj <ashok.raj@xxxxxxxxx>
---
 arch/x86/kvm/svm.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 0e68f0b..7c14471a 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -183,6 +183,8 @@ struct vcpu_svm {
 		u64 gs_base;
 	} host;
 
+	u64 spec_ctrl;
+
 	u32 *msrpm;
 
 	ulong nmi_iret_rip;
@@ -248,6 +250,7 @@ static const struct svm_direct_access_msrs {
 	{ .index = MSR_CSTAR,				.always = true  },
 	{ .index = MSR_SYSCALL_MASK,			.always = true  },
 #endif
+	{ .index = MSR_IA32_SPEC_CTRL,          .always = true  },
 	{ .index = MSR_IA32_LASTBRANCHFROMIP,		.always = false },
 	{ .index = MSR_IA32_LASTBRANCHTOIP,		.always = false },
 	{ .index = MSR_IA32_LASTINTFROMIP,		.always = false },
@@ -917,6 +920,9 @@ static void svm_vcpu_init_msrpm(u32 *msrpm)
 
 		set_msr_interception(msrpm, direct_access_msrs[i].index, 1, 1);
 	}
+
+	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL))
+		set_msr_interception(msrpm, MSR_IA32_SPEC_CTRL, 1, 1);
 }
 
 static void add_msr_offset(u32 offset)
@@ -3576,6 +3582,9 @@ 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;
@@ -3724,6 +3733,9 @@ 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;
 	case MSR_IA32_APICBASE:
 		if (kvm_vcpu_apicv_active(vcpu))
 			avic_update_vapic_bar(to_svm(vcpu), data);
@@ -4871,6 +4883,19 @@ static void svm_cancel_injection(struct kvm_vcpu *vcpu)
 	svm_complete_interrupts(svm);
 }
 
+
+/*
+ * Save guest value of spec_ctrl and also restore host value
+ */
+static void save_guest_spec_ctrl(struct vcpu_svm *svm)
+{
+	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL)) {
+		svm->spec_ctrl = spec_ctrl_get();
+		spec_ctrl_restriction_on();
+	} else
+		rmb();
+}
+
 static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -4910,6 +4935,14 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 
 	clgi();
 
+	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL)) {
+		/*
+		 * FIXME: lockdep_assert_irqs_disabled();
+		 */
+		WARN_ON_ONCE(!irqs_disabled());
+		spec_ctrl_set(svm->spec_ctrl);
+	}
+
 	local_irq_enable();
 
 	asm volatile (
@@ -4985,6 +5018,8 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 #endif
 		);
 
+	save_guest_spec_ctrl(svm);
+
 #ifdef CONFIG_X86_64
 	wrmsrl(MSR_GS_BASE, svm->host.gs_base);
 #else
-- 
2.7.4