KVM: x86: Move uret MSR slot management to common x86

Now that SVM and VMX both probe MSRs before "defining" user return slots
for them, consolidate the code for probe+define into common x86 and
eliminate the odd behavior of having the vendor code define the slot for
a given MSR.
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-14-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -1777,9 +1777,8 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low,
 		    unsigned long ipi_bitmap_high, u32 min,
 		    unsigned long icr, int op_64_bit);
 
-void kvm_define_user_return_msr(unsigned index, u32 msr);
+int kvm_add_user_return_msr(u32 msr);
 int kvm_find_user_return_msr(u32 msr);
-int kvm_probe_user_return_msr(u32 msr);
 int kvm_set_user_return_msr(unsigned index, u64 val, u64 mask);
 
 u64 kvm_scale_tsc(struct kvm_vcpu *vcpu, u64 tsc);

arch/x86/kvm/svm/svm.c

@@ -959,10 +959,7 @@ static __init int svm_hardware_setup(void)
 		kvm_tsc_scaling_ratio_frac_bits = 32;
 	}
 
-	if (!kvm_probe_user_return_msr(MSR_TSC_AUX)) {
-		tsc_aux_uret_slot = 0;
-		kvm_define_user_return_msr(tsc_aux_uret_slot, MSR_TSC_AUX);
-	}
+	tsc_aux_uret_slot = kvm_add_user_return_msr(MSR_TSC_AUX);
 
 	/* Check for pause filtering support */
 	if (!boot_cpu_has(X86_FEATURE_PAUSEFILTER)) {

arch/x86/kvm/vmx/vmx.c

@@ -454,9 +454,6 @@ static inline void vmx_segment_cache_clear(struct vcpu_vmx *vmx)
 
 static unsigned long host_idt_base;
 
-/* Number of user return MSRs that are actually supported in hardware. */
-static int vmx_nr_uret_msrs;
-
 #if IS_ENABLED(CONFIG_HYPERV)
 static bool __read_mostly enlightened_vmcs = true;
 module_param(enlightened_vmcs, bool, 0444);
@@ -1218,7 +1215,7 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 	 */
 	if (!vmx->guest_uret_msrs_loaded) {
 		vmx->guest_uret_msrs_loaded = true;
-		for (i = 0; i < vmx_nr_uret_msrs; ++i) {
+		for (i = 0; i < kvm_nr_uret_msrs; ++i) {
 			if (!vmx->guest_uret_msrs[i].load_into_hardware)
 				continue;
 
@@ -6921,7 +6918,7 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
 			goto free_vpid;
 	}
 
-	for (i = 0; i < vmx_nr_uret_msrs; ++i) {
+	for (i = 0; i < kvm_nr_uret_msrs; ++i) {
 		vmx->guest_uret_msrs[i].data = 0;
 		vmx->guest_uret_msrs[i].mask = -1ull;
 	}
@@ -7810,20 +7807,12 @@ static __init void vmx_setup_user_return_msrs(void)
 		MSR_EFER, MSR_TSC_AUX, MSR_STAR,
 		MSR_IA32_TSX_CTRL,
 	};
-	u32 msr;
 	int i;
 
 	BUILD_BUG_ON(ARRAY_SIZE(vmx_uret_msrs_list) != MAX_NR_USER_RETURN_MSRS);
 
-	for (i = 0; i < ARRAY_SIZE(vmx_uret_msrs_list); ++i) {
-		msr = vmx_uret_msrs_list[i];
-
-		if (kvm_probe_user_return_msr(msr))
-			continue;
-
-		kvm_define_user_return_msr(vmx_nr_uret_msrs, msr);
-		vmx_nr_uret_msrs++;
-	}
+	for (i = 0; i < ARRAY_SIZE(vmx_uret_msrs_list); ++i)
+		kvm_add_user_return_msr(vmx_uret_msrs_list[i]);
 }
 
 static __init int hardware_setup(void)

arch/x86/kvm/x86.c

@@ -336,7 +336,7 @@ static void kvm_on_user_return(struct user_return_notifier *urn)
 	}
 }
 
-int kvm_probe_user_return_msr(u32 msr)
+static int kvm_probe_user_return_msr(u32 msr)
 {
 	u64 val;
 	int ret;
@@ -350,16 +350,18 @@ int kvm_probe_user_return_msr(u32 msr)
 	preempt_enable();
 	return ret;
 }
-EXPORT_SYMBOL_GPL(kvm_probe_user_return_msr);
 
-void kvm_define_user_return_msr(unsigned slot, u32 msr)
+int kvm_add_user_return_msr(u32 msr)
 {
-	BUG_ON(slot >= KVM_MAX_NR_USER_RETURN_MSRS);
-	kvm_uret_msrs_list[slot] = msr;
-	if (slot >= kvm_nr_uret_msrs)
-		kvm_nr_uret_msrs = slot + 1;
+	BUG_ON(kvm_nr_uret_msrs >= KVM_MAX_NR_USER_RETURN_MSRS);
+
+	if (kvm_probe_user_return_msr(msr))
+		return -1;
+
+	kvm_uret_msrs_list[kvm_nr_uret_msrs] = msr;
+	return kvm_nr_uret_msrs++;
 }
-EXPORT_SYMBOL_GPL(kvm_define_user_return_msr);
+EXPORT_SYMBOL_GPL(kvm_add_user_return_msr);
 
 int kvm_find_user_return_msr(u32 msr)
 {
@@ -8132,6 +8134,7 @@ int kvm_arch_init(void *opaque)
 		printk(KERN_ERR "kvm: failed to allocate percpu kvm_user_return_msrs\n");
 		goto out_free_x86_emulator_cache;
 	}
+	kvm_nr_uret_msrs = 0;
 
 	r = kvm_mmu_module_init();
 	if (r)