KVM: x86: Calculate the supported xcr0 mask at load time

Add a new global variable, supported_xcr0, to track which xcr0 bits can
be exposed to the guest instead of calculating the mask on every call.
The supported bits are constant for a given instance of KVM.

This paves the way toward eliminating the ->mpx_supported() call in
kvm_mpx_supported(), e.g. eliminates multiple retpolines in VMX's nested
VM-Enter path, and eventually toward eliminating ->mpx_supported()
altogether.

No functional change intended.
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/cpuid.c

@@ -52,16 +52,6 @@ bool kvm_mpx_supported(void)
 }
 EXPORT_SYMBOL_GPL(kvm_mpx_supported);
 
-u64 kvm_supported_xcr0(void)
-{
-	u64 xcr0 = KVM_SUPPORTED_XCR0 & host_xcr0;
-
-	if (!kvm_mpx_supported())
-		xcr0 &= ~(XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR);
-
-	return xcr0;
-}
-
 #define F feature_bit
 
 int kvm_update_cpuid(struct kvm_vcpu *vcpu)
@@ -107,8 +97,7 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
 		vcpu->arch.guest_xstate_size = XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET;
 	} else {
 		vcpu->arch.guest_supported_xcr0 =
-			(best->eax | ((u64)best->edx << 32)) &
-			kvm_supported_xcr0();
+			(best->eax | ((u64)best->edx << 32)) & supported_xcr0;
 		vcpu->arch.guest_xstate_size = best->ebx =
 			xstate_required_size(vcpu->arch.xcr0, false);
 	}
@@ -633,14 +622,12 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 				goto out;
 		}
 		break;
-	case 0xd: {
-		u64 supported = kvm_supported_xcr0();
-
-		entry->eax &= supported;
-		entry->ebx = xstate_required_size(supported, false);
+	case 0xd:
+		entry->eax &= supported_xcr0;
+		entry->ebx = xstate_required_size(supported_xcr0, false);
 		entry->ecx = entry->ebx;
-		entry->edx &= supported >> 32;
-		if (!supported)
+		entry->edx &= supported_xcr0 >> 32;
+		if (!supported_xcr0)
 			break;
 
 		entry = do_host_cpuid(array, function, 1);
@@ -650,7 +637,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		entry->eax &= kvm_cpuid_D_1_eax_x86_features;
 		cpuid_mask(&entry->eax, CPUID_D_1_EAX);
 		if (entry->eax & (F(XSAVES)|F(XSAVEC)))
-			entry->ebx = xstate_required_size(supported, true);
+			entry->ebx = xstate_required_size(supported_xcr0, true);
 		else
 			entry->ebx = 0;
 		/* Saving XSS controlled state via XSAVES isn't supported. */
@@ -658,7 +645,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		entry->edx = 0;
 
 		for (i = 2; i < 64; ++i) {
-			if (!(supported & BIT_ULL(i)))
+			if (!(supported_xcr0 & BIT_ULL(i)))
 				continue;
 
 			entry = do_host_cpuid(array, function, i);
@@ -666,7 +653,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 				goto out;
 
 			/*
-			 * The @supported check above should have filtered out
+			 * The supported check above should have filtered out
 			 * invalid sub-leafs as well as sub-leafs managed by
 			 * IA32_XSS MSR.  Only XCR0-managed sub-leafs should
 			 * reach this point, and they should have a non-zero
@@ -681,7 +668,6 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 			entry->edx = 0;
 		}
 		break;
-	}
 	/* Intel PT */
 	case 0x14:
 		if (!f_intel_pt)

arch/x86/kvm/svm.c

@@ -1385,6 +1385,8 @@ static __init int svm_hardware_setup(void)
 
 	init_msrpm_offsets();
 
+	supported_xcr0 &= ~(XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR);
+
 	if (boot_cpu_has(X86_FEATURE_NX))
 		kvm_enable_efer_bits(EFER_NX);
 

arch/x86/kvm/vmx/vmx.c

@@ -7660,6 +7660,10 @@ static __init int hardware_setup(void)
 		WARN_ONCE(host_bndcfgs, "KVM: BNDCFGS in host will be lost");
 	}
 
+	if (!kvm_mpx_supported())
+		supported_xcr0 &= ~(XFEATURE_MASK_BNDREGS |
+				    XFEATURE_MASK_BNDCSR);
+
 	if (!cpu_has_vmx_vpid() || !cpu_has_vmx_invvpid() ||
 	    !(cpu_has_vmx_invvpid_single() || cpu_has_vmx_invvpid_global()))
 		enable_vpid = 0;

arch/x86/kvm/x86.c

@@ -181,6 +181,11 @@ struct kvm_shared_msrs {
 static struct kvm_shared_msrs_global __read_mostly shared_msrs_global;
 static struct kvm_shared_msrs __percpu *shared_msrs;
 
+#define KVM_SUPPORTED_XCR0     (XFEATURE_MASK_FP | XFEATURE_MASK_SSE \
+				| XFEATURE_MASK_YMM | XFEATURE_MASK_BNDREGS \
+				| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
+				| XFEATURE_MASK_PKRU)
+
 static u64 __read_mostly host_xss;
 
 struct kvm_stats_debugfs_item debugfs_entries[] = {
@@ -227,6 +232,8 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
 };
 
 u64 __read_mostly host_xcr0;
+u64 __read_mostly supported_xcr0;
+EXPORT_SYMBOL_GPL(supported_xcr0);
 
 struct kmem_cache *x86_fpu_cache;
 EXPORT_SYMBOL_GPL(x86_fpu_cache);
@@ -4114,8 +4121,7 @@ static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,
 		 * CPUID leaf 0xD, index 0, EDX:EAX.  This is for compatibility
 		 * with old userspace.
 		 */
-		if (xstate_bv & ~kvm_supported_xcr0() ||
-			mxcsr & ~mxcsr_feature_mask)
+		if (xstate_bv & ~supported_xcr0 || mxcsr & ~mxcsr_feature_mask)
 			return -EINVAL;
 		load_xsave(vcpu, (u8 *)guest_xsave->region);
 	} else {
@@ -7352,8 +7358,10 @@ int kvm_arch_init(void *opaque)
 
 	perf_register_guest_info_callbacks(&kvm_guest_cbs);
 
-	if (boot_cpu_has(X86_FEATURE_XSAVE))
+	if (boot_cpu_has(X86_FEATURE_XSAVE)) {
 		host_xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);
+		supported_xcr0 = host_xcr0 & KVM_SUPPORTED_XCR0;
+	}
 
 	kvm_lapic_init();
 	if (pi_inject_timer == -1)

arch/x86/kvm/x86.h

@@ -270,13 +270,8 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 			    int emulation_type, void *insn, int insn_len);
 enum exit_fastpath_completion handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu);
 
-#define KVM_SUPPORTED_XCR0     (XFEATURE_MASK_FP | XFEATURE_MASK_SSE \
-				| XFEATURE_MASK_YMM | XFEATURE_MASK_BNDREGS \
-				| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
-				| XFEATURE_MASK_PKRU)
 extern u64 host_xcr0;
-
-extern u64 kvm_supported_xcr0(void);
+extern u64 supported_xcr0;
 
 extern unsigned int min_timer_period_us;