[RFC PATCH 8/9] x86/kvm/vmx: Initialize SPEC_CTRL MASK for RRSBA

[Zhang Chen]

VMMs can address mitigations issues in migration pool by applying
the needed controls whenever the guest is operating on a newer
processor. If a guest is using retpoline to mitigate intra-mode BTI
in CPL0, the VMM can set RRSBA_DIS_S when the guest runs on hardware
which enumerates RRSBA.

Signed-off-by: Zhang Chen <chen.zhang@xxxxxxxxx>
---
 arch/x86/kvm/vmx/vmx.c | 57 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 56 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 6ed6b743be0e..fb0f3b1639b9 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2007,6 +2007,20 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 			return 1;
 		msr_info->data = vmx->msr_virtual_enumeration;
 		break;
+	case MSR_VIRTUAL_MITIGATION_ENUM:
+		if (!msr_info->host_initiated &&
+		    !(vmx->msr_virtual_enumeration &
+		    VIRT_ENUM_MITIGATION_CTRL_SUPPORT))
+			return 1;
+		msr_info->data = vmx->msr_virtual_mitigation_enum;
+		break;
+	case MSR_VIRTUAL_MITIGATION_CTRL:
+		if (!msr_info->host_initiated &&
+		    !(vmx->msr_virtual_enumeration &
+		    VIRT_ENUM_MITIGATION_CTRL_SUPPORT))
+			return 1;
+		msr_info->data = vmx->msr_virtual_mitigation_ctrl;
+		break;
 	default:
 	find_uret_msr:
 		msr = vmx_find_uret_msr(vmx, msr_info->index);
@@ -2056,7 +2070,7 @@ 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;
+	u64 data = msr_info->data, arch_msr;
 	u32 index;
 
 	switch (msr_index) {
@@ -2390,6 +2404,46 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		vmx->msr_virtual_enumeration = data &
 						VIRT_ENUM_MITIGATION_CTRL_SUPPORT;
 		break;
+	case MSR_VIRTUAL_MITIGATION_ENUM:
+		if (msr_info->host_initiated &&
+		    !(vmx->msr_virtual_enumeration &
+		    VIRT_ENUM_MITIGATION_CTRL_SUPPORT))
+			return 1;
+		if (data & ~MITI_ENUM_SUPPORTED)
+			return 1;
+		vmx->msr_virtual_mitigation_enum = data;
+		break;
+	case MSR_VIRTUAL_MITIGATION_CTRL:
+		if (!msr_info->host_initiated &&
+		    !(vmx->msr_virtual_enumeration &
+		    VIRT_ENUM_MITIGATION_CTRL_SUPPORT))
+			return 1;
+		if (data & ~MITI_CTRL_USED)
+			return 1;
+
+		if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
+			rdmsrl(MSR_IA32_ARCH_CAPABILITIES, arch_msr);
+
+		if (data & MITI_CTRL_RETPOLINE_S_USED &&
+		    boot_cpu_has(X86_FEATURE_RRSBA_CTRL) &&
+		    arch_msr & ARCH_CAP_RRSBA)
+			vmx->spec_ctrl_mask |= SPEC_CTRL_RRSBA_DIS_S;
+		else
+			vmx->spec_ctrl_mask &= ~SPEC_CTRL_RRSBA_DIS_S;
+
+		if (cpu_has_virt_spec_ctrl()) {
+			vmcs_write64(IA32_SPEC_CTRL_MASK, vmx->spec_ctrl_mask);
+		} else if (vmx->spec_ctrl_mask) {
+			pr_err_once("Virtual spec ctrl is missing. Cannot keep "
+					"bits in %llx always set\n",
+					vmx->spec_ctrl_mask);
+			vmx->spec_ctrl_mask = 0;
+		}
+
+		vmx->spec_ctrl = vmx->spec_ctrl | vmx->spec_ctrl_mask;
+
+		vmx->msr_virtual_mitigation_ctrl = data;
+		break;
 
 	default:
 	find_uret_msr:
@@ -4774,6 +4828,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 
 	vmx->rmode.vm86_active = 0;
 
+	vmx->msr_virtual_mitigation_ctrl = 0;
 	if (cpu_has_virt_spec_ctrl()) {
 		vmx->spec_ctrl_mask = 0;
 		vmcs_write64(IA32_SPEC_CTRL_MASK, vmx->spec_ctrl_mask);
-- 
2.25.1