target/i386: add support for MSR_IA32_TSX_CTRL

The MSR_IA32_TSX_CTRL MSR can be used to hide TSX (also known as the
Trusty Side-channel Extension).  By virtualizing the MSR, KVM guests
can disable TSX and avoid paying the price of mitigating TSX-based
attacks on microarchitectural side channels.

Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/cpu.c

@@ -1204,7 +1204,7 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
         .type = MSR_FEATURE_WORD,
         .feat_names = {
             "rdctl-no", "ibrs-all", "rsba", "skip-l1dfl-vmentry",
-            "ssb-no", "mds-no", "pschange-mc-no", NULL,
+            "ssb-no", "mds-no", "pschange-mc-no", "tsx-ctrl",
             "taa-no", NULL, NULL, NULL,
             NULL, NULL, NULL, NULL,
             NULL, NULL, NULL, NULL,

target/i386/cpu.h

@@ -349,7 +349,11 @@ typedef enum X86Seg {
 #define MSR_VIRT_SSBD                   0xc001011f
 #define MSR_IA32_PRED_CMD               0x49
 #define MSR_IA32_CORE_CAPABILITY        0xcf
+
 #define MSR_IA32_ARCH_CAPABILITIES      0x10a
+#define ARCH_CAP_TSX_CTRL_MSR		(1<<7)
+
+#define MSR_IA32_TSX_CTRL		0x122
 #define MSR_IA32_TSCDEADLINE            0x6e0
 
 #define FEATURE_CONTROL_LOCKED                    (1<<0)
@@ -1449,6 +1453,7 @@ typedef struct CPUX86State {
     uint64_t msr_smi_count;
 
     uint32_t pkru;
+    uint32_t tsx_ctrl;
 
     uint64_t spec_ctrl;
     uint64_t virt_ssbd;

target/i386/kvm.c

@@ -97,6 +97,7 @@ static bool has_msr_hv_reenlightenment;
 static bool has_msr_xss;
 static bool has_msr_umwait;
 static bool has_msr_spec_ctrl;
+static bool has_msr_tsx_ctrl;
 static bool has_msr_virt_ssbd;
 static bool has_msr_smi_count;
 static bool has_msr_arch_capabs;
@@ -2036,6 +2037,9 @@ static int kvm_get_supported_msrs(KVMState *s)
             case MSR_IA32_SPEC_CTRL:
                 has_msr_spec_ctrl = true;
                 break;
+            case MSR_IA32_TSX_CTRL:
+                has_msr_tsx_ctrl = true;
+                break;
             case MSR_VIRT_SSBD:
                 has_msr_virt_ssbd = true;
                 break;
@@ -2694,6 +2698,9 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
     if (has_msr_spec_ctrl) {
         kvm_msr_entry_add(cpu, MSR_IA32_SPEC_CTRL, env->spec_ctrl);
     }
+    if (has_msr_tsx_ctrl) {
+        kvm_msr_entry_add(cpu, MSR_IA32_TSX_CTRL, env->tsx_ctrl);
+    }
     if (has_msr_virt_ssbd) {
         kvm_msr_entry_add(cpu, MSR_VIRT_SSBD, env->virt_ssbd);
     }
@@ -3110,6 +3117,9 @@ static int kvm_get_msrs(X86CPU *cpu)
     if (has_msr_spec_ctrl) {
         kvm_msr_entry_add(cpu, MSR_IA32_SPEC_CTRL, 0);
     }
+    if (has_msr_tsx_ctrl) {
+        kvm_msr_entry_add(cpu, MSR_IA32_TSX_CTRL, 0);
+    }
     if (has_msr_virt_ssbd) {
         kvm_msr_entry_add(cpu, MSR_VIRT_SSBD, 0);
     }
@@ -3502,6 +3512,9 @@ static int kvm_get_msrs(X86CPU *cpu)
         case MSR_IA32_SPEC_CTRL:
             env->spec_ctrl = msrs[i].data;
             break;
+        case MSR_IA32_TSX_CTRL:
+            env->tsx_ctrl = msrs[i].data;
+            break;
         case MSR_VIRT_SSBD:
             env->virt_ssbd = msrs[i].data;
             break;

target/i386/machine.c

@@ -1293,6 +1293,25 @@ static const VMStateDescription vmstate_efer32 = {
 };
 #endif
 
+static bool msr_tsx_ctrl_needed(void *opaque)
+{
+    X86CPU *cpu = opaque;
+    CPUX86State *env = &cpu->env;
+
+    return env->features[FEAT_ARCH_CAPABILITIES] & ARCH_CAP_TSX_CTRL_MSR;
+}
+
+static const VMStateDescription vmstate_msr_tsx_ctrl = {
+    .name = "cpu/msr_tsx_ctrl",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = msr_tsx_ctrl_needed,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32(env.tsx_ctrl, X86CPU),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 VMStateDescription vmstate_x86_cpu = {
     .name = "cpu",
     .version_id = 12,
@@ -1427,6 +1446,7 @@ VMStateDescription vmstate_x86_cpu = {
 #ifdef CONFIG_KVM
         &vmstate_nested_state,
 #endif
+        &vmstate_msr_tsx_ctrl,
         NULL
     }
 };