[PATCH 3/5] x86/ibrs: Add direct access support for MSR_IA32_SPEC_CTRL

[Ashok Raj]

Add direct access to MSR_IA32_SPEC_CTRL from a guest. Also save/restore
IBRS values during exits and guest resume path.

Rebasing based on Tim's patch

Signed-off-by: Ashok Raj <ashok.raj@xxxxxxxxx>
---
 arch/x86/kvm/cpuid.c |  3 ++-
 arch/x86/kvm/vmx.c   | 41 +++++++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/x86.c   |  1 +
 3 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 0099e10..6fa81c7 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -70,6 +70,7 @@ u64 kvm_supported_xcr0(void)
 /* These are scattered features in cpufeatures.h. */
 #define KVM_CPUID_BIT_AVX512_4VNNIW     2
 #define KVM_CPUID_BIT_AVX512_4FMAPS     3
+#define KVM_CPUID_BIT_SPEC_CTRL        26
 #define KF(x) bit(KVM_CPUID_BIT_##x)
 
 int kvm_update_cpuid(struct kvm_vcpu *vcpu)
@@ -392,7 +393,7 @@ 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 =
-		KF(AVX512_4VNNIW) | KF(AVX512_4FMAPS);
+		KF(AVX512_4VNNIW) | KF(AVX512_4FMAPS) | KF(SPEC_CTRL);
 
 	/* 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 62ee436..1913896 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -50,6 +50,7 @@
 #include <asm/apic.h>
 #include <asm/irq_remapping.h>
 #include <asm/mmu_context.h>
+#include <asm/spec_ctrl.h>
 
 #include "trace.h"
 #include "pmu.h"
@@ -579,6 +580,7 @@ struct vcpu_vmx {
 	u32 vm_entry_controls_shadow;
 	u32 vm_exit_controls_shadow;
 	u32 secondary_exec_control;
+	u64 spec_ctrl;
 
 	/*
 	 * loaded_vmcs points to the VMCS currently used in this vcpu. For a
@@ -3259,6 +3261,9 @@ 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_SPEC_CTRL:
+		msr_info->data = to_vmx(vcpu)->spec_ctrl;
+		break;
 	case MSR_IA32_SYSENTER_CS:
 		msr_info->data = vmcs_read32(GUEST_SYSENTER_CS);
 		break;
@@ -3366,6 +3371,9 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_IA32_TSC:
 		kvm_write_tsc(vcpu, msr_info);
 		break;
+	case MSR_IA32_SPEC_CTRL:
+		to_vmx(vcpu)->spec_ctrl = msr_info->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))
@@ -6790,6 +6798,13 @@ static __init int hardware_setup(void)
 		kvm_tsc_scaling_ratio_frac_bits = 48;
 	}
 
+	/*
+	 * If feature is available then setup MSR_IA32_SPEC_CTRL to be in
+	 * passthrough mode for the guest.
+	 */
+	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL))
+		vmx_disable_intercept_for_msr(MSR_IA32_SPEC_CTRL, false);
+
 	vmx_disable_intercept_for_msr(MSR_FS_BASE, false);
 	vmx_disable_intercept_for_msr(MSR_GS_BASE, false);
 	vmx_disable_intercept_for_msr(MSR_KERNEL_GS_BASE, true);
@@ -9242,6 +9257,15 @@ static void vmx_arm_hv_timer(struct kvm_vcpu *vcpu)
 	vmcs_write32(VMX_PREEMPTION_TIMER_VALUE, delta_tsc);
 }
 
+static void save_guest_spec_ctrl(struct vcpu_vmx *vmx)
+{
+	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL)) {
+		vmx->spec_ctrl = spec_ctrl_get();
+		spec_ctrl_restriction_on();
+	} else
+		rmb();
+}
+
 static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -9298,6 +9322,21 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
 	vmx_arm_hv_timer(vcpu);
 
 	vmx->__launched = vmx->loaded_vmcs->launched;
+
+	/*
+	 * Just update whatever the value was set for the MSR in guest.
+	 * If this is unlaunched: Assume that initialized value is 0.
+	 * IRQ's also need to be disabled. If guest value is 0, an interrupt
+	 * could start running in unprotected mode (i.e with IBRS=0).
+	 */
+	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL)) {
+		/*
+		 * FIXME: lockdep_assert_irqs_disabled();
+		 */
+		WARN_ON_ONCE(!irqs_disabled());
+		spec_ctrl_set(vmx->spec_ctrl);
+	}
+
 	asm(
 		/* Store host registers */
 		"push %%" _ASM_DX "; push %%" _ASM_BP ";"
@@ -9403,6 +9442,8 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
 #endif
 	      );
 
+	save_guest_spec_ctrl(vmx);
+
 	/* MSR_IA32_DEBUGCTLMSR is zeroed on vmexit. Restore it if needed */
 	if (debugctlmsr)
 		update_debugctlmsr(debugctlmsr);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 03869eb..9ffb9d6 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_SPEC_CTRL,
 };
 
 static unsigned num_msrs_to_save;
-- 
2.7.4