KVM: x86: introduce num_emulated_msrs

We will want to filter away MSR_IA32_SMBASE from the emulated_msrs if
the host CPU does not support SMM virtualization.  Introduce the
logic to do that, and also move paravirt MSRs to emulated_msrs for
simplicity and to get rid of KVM_SAVE_MSRS_BEGIN.
Reviewed-by: NRadim Krčmář <rkrcmar@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -925,17 +925,11 @@ EXPORT_SYMBOL_GPL(kvm_rdpmc);
  *
  * This list is modified at module load time to reflect the
  * capabilities of the host cpu. This capabilities test skips MSRs that are
- * kvm-specific. Those are put in the beginning of the list.
+ * kvm-specific. Those are put in emulated_msrs; filtering of emulated_msrs
+ * may depend on host virtualization features rather than host cpu features.
  */
 
-#define KVM_SAVE_MSRS_BEGIN	12
 static u32 msrs_to_save[] = {
-	MSR_KVM_SYSTEM_TIME, MSR_KVM_WALL_CLOCK,
-	MSR_KVM_SYSTEM_TIME_NEW, MSR_KVM_WALL_CLOCK_NEW,
-	HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL,
-	HV_X64_MSR_TIME_REF_COUNT, HV_X64_MSR_REFERENCE_TSC,
-	HV_X64_MSR_APIC_ASSIST_PAGE, MSR_KVM_ASYNC_PF_EN, MSR_KVM_STEAL_TIME,
-	MSR_KVM_PV_EOI_EN,
 	MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
 	MSR_STAR,
 #ifdef CONFIG_X86_64
@@ -947,7 +941,14 @@ static u32 msrs_to_save[] = {
 
 static unsigned num_msrs_to_save;
 
-static const u32 emulated_msrs[] = {
+static u32 emulated_msrs[] = {
+	MSR_KVM_SYSTEM_TIME, MSR_KVM_WALL_CLOCK,
+	MSR_KVM_SYSTEM_TIME_NEW, MSR_KVM_WALL_CLOCK_NEW,
+	HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL,
+	HV_X64_MSR_TIME_REF_COUNT, HV_X64_MSR_REFERENCE_TSC,
+	HV_X64_MSR_APIC_ASSIST_PAGE, MSR_KVM_ASYNC_PF_EN, MSR_KVM_STEAL_TIME,
+	MSR_KVM_PV_EOI_EN,
+
 	MSR_IA32_TSC_ADJUST,
 	MSR_IA32_TSCDEADLINE,
 	MSR_IA32_MISC_ENABLE,
@@ -955,6 +956,8 @@ static const u32 emulated_msrs[] = {
 	MSR_IA32_MCG_CTL,
 };
 
+static unsigned num_emulated_msrs;
+
 bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer)
 {
 	if (efer & efer_reserved_bits)
@@ -2928,7 +2931,7 @@ long kvm_arch_dev_ioctl(struct file *filp,
 		if (copy_from_user(&msr_list, user_msr_list, sizeof msr_list))
 			goto out;
 		n = msr_list.nmsrs;
-		msr_list.nmsrs = num_msrs_to_save + ARRAY_SIZE(emulated_msrs);
+		msr_list.nmsrs = num_msrs_to_save + num_emulated_msrs;
 		if (copy_to_user(user_msr_list, &msr_list, sizeof msr_list))
 			goto out;
 		r = -E2BIG;
@@ -2940,7 +2943,7 @@ long kvm_arch_dev_ioctl(struct file *filp,
 			goto out;
 		if (copy_to_user(user_msr_list->indices + num_msrs_to_save,
 				 &emulated_msrs,
-				 ARRAY_SIZE(emulated_msrs) * sizeof(u32)))
+				 num_emulated_msrs * sizeof(u32)))
 			goto out;
 		r = 0;
 		break;
@@ -4206,8 +4209,7 @@ static void kvm_init_msr_list(void)
 	u32 dummy[2];
 	unsigned i, j;
 
-	/* skip the first msrs in the list. KVM-specific */
-	for (i = j = KVM_SAVE_MSRS_BEGIN; i < ARRAY_SIZE(msrs_to_save); i++) {
+	for (i = j = 0; i < ARRAY_SIZE(msrs_to_save); i++) {
 		if (rdmsr_safe(msrs_to_save[i], &dummy[0], &dummy[1]) < 0)
 			continue;
 
@@ -4232,6 +4234,18 @@ static void kvm_init_msr_list(void)
 		j++;
 	}
 	num_msrs_to_save = j;
+
+	for (i = j = 0; i < ARRAY_SIZE(emulated_msrs); i++) {
+		switch (emulated_msrs[i]) {
+		default:
+			break;
+		}
+
+		if (j < i)
+			emulated_msrs[j] = emulated_msrs[i];
+		j++;
+	}
+	num_emulated_msrs = j;
 }
 
 static int vcpu_mmio_write(struct kvm_vcpu *vcpu, gpa_t addr, int len,