KVM: VMX: Stub out enable_evmcs static key for CONFIG_HYPERV=n

Wrap enable_evmcs in a helper and stub it out when CONFIG_HYPERV=n in
order to eliminate the static branch nop placeholders.  clang-14 is clever
enough to elide the nop, but gcc-12 is not.  Stubbing out the key reduces
the size of kvm-intel.ko by ~7.5% (200KiB) when compiled with gcc-12
(there are a _lot_ of VMCS accesses throughout KVM).
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230211003534.564198-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/hyperv.c

@@ -118,8 +118,6 @@
 
 #define EVMCS1_SUPPORTED_VMFUNC (0)
 
-DEFINE_STATIC_KEY_FALSE(enable_evmcs);
-
 #define EVMCS1_OFFSET(x) offsetof(struct hv_enlightened_vmcs, x)
 #define EVMCS1_FIELD(number, name, clean_field)[ROL16(number, 6)] = \
 		{EVMCS1_OFFSET(name), clean_field}
@@ -611,6 +609,8 @@ int nested_evmcs_check_controls(struct vmcs12 *vmcs12)
 }
 
 #if IS_ENABLED(CONFIG_HYPERV)
+DEFINE_STATIC_KEY_FALSE(enable_evmcs);
+
 /*
  * KVM on Hyper-V always uses the latest known eVMCSv1 revision, the assumption
  * is: in case a feature has corresponding fields in eVMCS described and it was

arch/x86/kvm/vmx/hyperv.h

@@ -16,8 +16,6 @@
 
 struct vmcs_config;
 
-DECLARE_STATIC_KEY_FALSE(enable_evmcs);
-
 #define current_evmcs ((struct hv_enlightened_vmcs *)this_cpu_read(current_vmcs))
 
 #define KVM_EVMCS_VERSION 1
@@ -69,6 +67,13 @@ static inline u64 evmcs_read_any(struct hv_enlightened_vmcs *evmcs,
 
 #if IS_ENABLED(CONFIG_HYPERV)
 
+DECLARE_STATIC_KEY_FALSE(enable_evmcs);
+
+static __always_inline bool kvm_is_using_evmcs(void)
+{
+	return static_branch_unlikely(&enable_evmcs);
+}
+
 static __always_inline int get_evmcs_offset(unsigned long field,
 					    u16 *clean_field)
 {
@@ -158,6 +163,7 @@ static inline void evmcs_load(u64 phys_addr)
 
 void evmcs_sanitize_exec_ctrls(struct vmcs_config *vmcs_conf);
 #else /* !IS_ENABLED(CONFIG_HYPERV) */
+static __always_inline bool kvm_is_using_evmcs(void) { return false; }
 static __always_inline void evmcs_write64(unsigned long field, u64 value) {}
 static __always_inline void evmcs_write32(unsigned long field, u32 value) {}
 static __always_inline void evmcs_write16(unsigned long field, u16 value) {}

arch/x86/kvm/vmx/vmx.c

@@ -595,7 +595,7 @@ static void hv_reset_evmcs(void)
 {
 	struct hv_vp_assist_page *vp_ap;
 
-	if (!static_branch_unlikely(&enable_evmcs))
+	if (!kvm_is_using_evmcs())
 		return;
 
 	/*
@@ -2816,8 +2816,7 @@ static int vmx_hardware_enable(void)
 	 * This can happen if we hot-added a CPU but failed to allocate
 	 * VP assist page for it.
 	 */
-	if (static_branch_unlikely(&enable_evmcs) &&
-	    !hv_get_vp_assist_page(cpu))
+	if (kvm_is_using_evmcs() && !hv_get_vp_assist_page(cpu))
 		return -EFAULT;
 
 	intel_pt_handle_vmx(1);
@@ -2869,7 +2868,7 @@ struct vmcs *alloc_vmcs_cpu(bool shadow, int cpu, gfp_t flags)
 	memset(vmcs, 0, vmcs_config.size);
 
 	/* KVM supports Enlightened VMCS v1 only */
-	if (static_branch_unlikely(&enable_evmcs))
+	if (kvm_is_using_evmcs())
 		vmcs->hdr.revision_id = KVM_EVMCS_VERSION;
 	else
 		vmcs->hdr.revision_id = vmcs_config.revision_id;
@@ -2964,7 +2963,7 @@ static __init int alloc_kvm_area(void)
 		 * still be marked with revision_id reported by
 		 * physical CPU.
 		 */
-		if (static_branch_unlikely(&enable_evmcs))
+		if (kvm_is_using_evmcs())
 			vmcs->hdr.revision_id = vmcs_config.revision_id;
 
 		per_cpu(vmxarea, cpu) = vmcs;
@@ -3931,7 +3930,7 @@ static void vmx_msr_bitmap_l01_changed(struct vcpu_vmx *vmx)
 	 * 'Enlightened MSR Bitmap' feature L0 needs to know that MSR
 	 * bitmap has changed.
 	 */
-	if (IS_ENABLED(CONFIG_HYPERV) && static_branch_unlikely(&enable_evmcs)) {
+	if (kvm_is_using_evmcs()) {
 		struct hv_enlightened_vmcs *evmcs = (void *)vmx->vmcs01.vmcs;
 
 		if (evmcs->hv_enlightenments_control.msr_bitmap)
@@ -7310,7 +7309,7 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
 	vmx_vcpu_enter_exit(vcpu, __vmx_vcpu_run_flags(vmx));
 
 	/* All fields are clean at this point */
-	if (static_branch_unlikely(&enable_evmcs)) {
+	if (kvm_is_using_evmcs()) {
 		current_evmcs->hv_clean_fields |=
 			HV_VMX_ENLIGHTENED_CLEAN_FIELD_ALL;
 
@@ -7440,7 +7439,7 @@ static int vmx_vcpu_create(struct kvm_vcpu *vcpu)
 	 * feature only for vmcs01, KVM currently isn't equipped to realize any
 	 * performance benefits from enabling it for vmcs02.
 	 */
-	if (IS_ENABLED(CONFIG_HYPERV) && static_branch_unlikely(&enable_evmcs) &&
+	if (kvm_is_using_evmcs() &&
 	    (ms_hyperv.nested_features & HV_X64_NESTED_MSR_BITMAP)) {
 		struct hv_enlightened_vmcs *evmcs = (void *)vmx->vmcs01.vmcs;
 

arch/x86/kvm/vmx/vmx_ops.h

@@ -147,7 +147,7 @@ static __always_inline unsigned long __vmcs_readl(unsigned long field)
 static __always_inline u16 vmcs_read16(unsigned long field)
 {
 	vmcs_check16(field);
-	if (static_branch_unlikely(&enable_evmcs))
+	if (kvm_is_using_evmcs())
 		return evmcs_read16(field);
 	return __vmcs_readl(field);
 }
@@ -155,7 +155,7 @@ static __always_inline u16 vmcs_read16(unsigned long field)
 static __always_inline u32 vmcs_read32(unsigned long field)
 {
 	vmcs_check32(field);
-	if (static_branch_unlikely(&enable_evmcs))
+	if (kvm_is_using_evmcs())
 		return evmcs_read32(field);
 	return __vmcs_readl(field);
 }
@@ -163,7 +163,7 @@ static __always_inline u32 vmcs_read32(unsigned long field)
 static __always_inline u64 vmcs_read64(unsigned long field)
 {
 	vmcs_check64(field);
-	if (static_branch_unlikely(&enable_evmcs))
+	if (kvm_is_using_evmcs())
 		return evmcs_read64(field);
 #ifdef CONFIG_X86_64
 	return __vmcs_readl(field);
@@ -175,7 +175,7 @@ static __always_inline u64 vmcs_read64(unsigned long field)
 static __always_inline unsigned long vmcs_readl(unsigned long field)
 {
 	vmcs_checkl(field);
-	if (static_branch_unlikely(&enable_evmcs))
+	if (kvm_is_using_evmcs())
 		return evmcs_read64(field);
 	return __vmcs_readl(field);
 }
@@ -222,7 +222,7 @@ static __always_inline void __vmcs_writel(unsigned long field, unsigned long val
 static __always_inline void vmcs_write16(unsigned long field, u16 value)
 {
 	vmcs_check16(field);
-	if (static_branch_unlikely(&enable_evmcs))
+	if (kvm_is_using_evmcs())
 		return evmcs_write16(field, value);
 
 	__vmcs_writel(field, value);
@@ -231,7 +231,7 @@ static __always_inline void vmcs_write16(unsigned long field, u16 value)
 static __always_inline void vmcs_write32(unsigned long field, u32 value)
 {
 	vmcs_check32(field);
-	if (static_branch_unlikely(&enable_evmcs))
+	if (kvm_is_using_evmcs())
 		return evmcs_write32(field, value);
 
 	__vmcs_writel(field, value);
@@ -240,7 +240,7 @@ static __always_inline void vmcs_write32(unsigned long field, u32 value)
 static __always_inline void vmcs_write64(unsigned long field, u64 value)
 {
 	vmcs_check64(field);
-	if (static_branch_unlikely(&enable_evmcs))
+	if (kvm_is_using_evmcs())
 		return evmcs_write64(field, value);
 
 	__vmcs_writel(field, value);
@@ -252,7 +252,7 @@ static __always_inline void vmcs_write64(unsigned long field, u64 value)
 static __always_inline void vmcs_writel(unsigned long field, unsigned long value)
 {
 	vmcs_checkl(field);
-	if (static_branch_unlikely(&enable_evmcs))
+	if (kvm_is_using_evmcs())
 		return evmcs_write64(field, value);
 
 	__vmcs_writel(field, value);
@@ -262,7 +262,7 @@ static __always_inline void vmcs_clear_bits(unsigned long field, u32 mask)
 {
 	BUILD_BUG_ON_MSG(__builtin_constant_p(field) && ((field) & 0x6000) == 0x2000,
 			 "vmcs_clear_bits does not support 64-bit fields");
-	if (static_branch_unlikely(&enable_evmcs))
+	if (kvm_is_using_evmcs())
 		return evmcs_write32(field, evmcs_read32(field) & ~mask);
 
 	__vmcs_writel(field, __vmcs_readl(field) & ~mask);
@@ -272,7 +272,7 @@ static __always_inline void vmcs_set_bits(unsigned long field, u32 mask)
 {
 	BUILD_BUG_ON_MSG(__builtin_constant_p(field) && ((field) & 0x6000) == 0x2000,
 			 "vmcs_set_bits does not support 64-bit fields");
-	if (static_branch_unlikely(&enable_evmcs))
+	if (kvm_is_using_evmcs())
 		return evmcs_write32(field, evmcs_read32(field) | mask);
 
 	__vmcs_writel(field, __vmcs_readl(field) | mask);
@@ -289,7 +289,7 @@ static inline void vmcs_load(struct vmcs *vmcs)
 {
 	u64 phys_addr = __pa(vmcs);
 
-	if (static_branch_unlikely(&enable_evmcs))
+	if (kvm_is_using_evmcs())
 		return evmcs_load(phys_addr);
 
 	vmx_asm1(vmptrld, "m"(phys_addr), vmcs, phys_addr);