[RFC PATCH v2 08/11] KVM: VMX: Advertise MITI_ENUM_RETPOLINE_S_SUPPORT

[Chao Gao]

Allow guest to query if the underying VMM understands Retpoline and
report the statue of Retpoline in suprevisor mode i.e. CPL < 3 via
MSR_VIRTUAL_MITIGATION_ENUM/CTRL.

Disable RRSBA behavior by setting RRSBA_DIS_S for guest if guest is
using retpoline and the processor has the behavior.

Signed-off-by: Zhang Chen <chen.zhang@xxxxxxxxx>
Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
Tested-by: Jiaan Lu <jiaan.lu@xxxxxxxxx>
---
 arch/x86/kvm/vmx/vmx.c | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 980498c4c30c..25afb4c3e55e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1944,8 +1944,8 @@ static inline bool is_vmx_feature_control_msr_valid(struct vcpu_vmx *vmx,
 }
 
 #define VIRTUAL_ENUMERATION_VALID_BITS	VIRT_ENUM_MITIGATION_CTRL_SUPPORT
-#define MITI_ENUM_VALID_BITS		0ULL
-#define MITI_CTRL_VALID_BITS		0ULL
+#define MITI_ENUM_VALID_BITS		MITI_ENUM_RETPOLINE_S_SUPPORT
+#define MITI_CTRL_VALID_BITS		MITI_CTRL_RETPOLINE_S_USED
 
 static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
 {
@@ -2173,7 +2173,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	struct vmx_uret_msr *msr;
 	int ret = 0;
 	u32 msr_index = msr_info->index;
-	u64 data = msr_info->data, spec_ctrl_mask;
+	u64 data = msr_info->data, arch_msr = 0, spec_ctrl_mask = 0;
 	u32 index;
 
 	switch (msr_index) {
@@ -2488,6 +2488,24 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		if (data & ~MITI_CTRL_VALID_BITS)
 			return 1;
 
+		if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
+			rdmsrl(MSR_IA32_ARCH_CAPABILITIES, arch_msr);
+
+		if (data & MITI_CTRL_RETPOLINE_S_USED &&
+		    kvm_cpu_cap_has(X86_FEATURE_RRSBA_CTRL) &&
+		    arch_msr & ARCH_CAP_RRSBA)
+			spec_ctrl_mask |= SPEC_CTRL_RRSBA_DIS_S;
+
+		/*
+		 * Intercept IA32_SPEC_CTRL to disallow guest from changing
+		 * certain bits.
+		 */
+		if (spec_ctrl_mask && !cpu_has_spec_ctrl_virt())
+			vmx_enable_intercept_for_msr(vcpu, MSR_IA32_SPEC_CTRL, MSR_TYPE_RW);
+
+		vmx_set_spec_ctrl_mask(vmx, spec_ctrl_mask);
+		vmx_set_guest_spec_ctrl(vmx, vmx_get_guest_spec_ctrl(vmx));
+
 		vmx->msr_virtual_mitigation_ctrl = data;
 		break;
 	default:
-- 
2.40.0