KVM: x86: Add dedicated emulator helpers for querying CPUID features

Add feature-specific helpers for querying guest CPUID support from the
emulator instead of having the emulator do a full CPUID and perform its
own bit tests.  The primary motivation is to eliminate the emulator's
usage of bit() so that future patches can add more extensive build-time
assertions on the usage of bit() without having to expose yet more code
to the emulator.

Note, providing a generic guest_cpuid_has() to the emulator doesn't work
due to the existing built-time assertions in guest_cpuid_has(), which
require the feature being checked to be a compile-time constant.

No functional change intended.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_emulate.h

@@ -222,6 +222,10 @@ struct x86_emulate_ops {
 
 	bool (*get_cpuid)(struct x86_emulate_ctxt *ctxt, u32 *eax, u32 *ebx,
 			  u32 *ecx, u32 *edx, bool check_limit);
+	bool (*guest_has_long_mode)(struct x86_emulate_ctxt *ctxt);
+	bool (*guest_has_movbe)(struct x86_emulate_ctxt *ctxt);
+	bool (*guest_has_fxsr)(struct x86_emulate_ctxt *ctxt);
+
 	void (*set_nmi_mask)(struct x86_emulate_ctxt *ctxt, bool masked);
 
 	unsigned (*get_hflags)(struct x86_emulate_ctxt *ctxt);

arch/x86/kvm/emulate.c

@@ -2348,12 +2348,7 @@ static int em_lseg(struct x86_emulate_ctxt *ctxt)
 static int emulator_has_longmode(struct x86_emulate_ctxt *ctxt)
 {
 #ifdef CONFIG_X86_64
-	u32 eax, ebx, ecx, edx;
+	return ctxt->ops->guest_has_long_mode(ctxt);
-
-	eax = 0x80000001;
-	ecx = 0;
-	ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx, false);
-	return edx & bit(X86_FEATURE_LM);
 #else
 	return false;
 #endif
@@ -3618,18 +3613,11 @@ static int em_mov(struct x86_emulate_ctxt *ctxt)
 	return X86EMUL_CONTINUE;
 }
 
-#define FFL(x) bit(X86_FEATURE_##x)
-
 static int em_movbe(struct x86_emulate_ctxt *ctxt)
 {
-	u32 ebx, ecx, edx, eax = 1;
 	u16 tmp;
 
-	/*
+	if (!ctxt->ops->guest_has_movbe(ctxt))
-	 * Check MOVBE is set in the guest-visible CPUID leaf.
-	 */
-	ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx, false);
-	if (!(ecx & FFL(MOVBE)))
 		return emulate_ud(ctxt);
 
 	switch (ctxt->op_bytes) {
@@ -4027,10 +4015,7 @@ static int em_movsxd(struct x86_emulate_ctxt *ctxt)
 
 static int check_fxsr(struct x86_emulate_ctxt *ctxt)
 {
-	u32 eax = 1, ebx, ecx = 0, edx;
+	if (!ctxt->ops->guest_has_fxsr(ctxt))
-
-	ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx, false);
-	if (!(edx & FFL(FXSR)))
 		return emulate_ud(ctxt);
 
 	if (ctxt->ops->get_cr(ctxt, 0) & (X86_CR0_TS | X86_CR0_EM))

arch/x86/kvm/x86.c

@@ -6245,6 +6245,21 @@ static bool emulator_get_cpuid(struct x86_emulate_ctxt *ctxt,
 	return kvm_cpuid(emul_to_vcpu(ctxt), eax, ebx, ecx, edx, check_limit);
 }
 
+static bool emulator_guest_has_long_mode(struct x86_emulate_ctxt *ctxt)
+{
+	return guest_cpuid_has(emul_to_vcpu(ctxt), X86_FEATURE_LM);
+}
+
+static bool emulator_guest_has_movbe(struct x86_emulate_ctxt *ctxt)
+{
+	return guest_cpuid_has(emul_to_vcpu(ctxt), X86_FEATURE_MOVBE);
+}
+
+static bool emulator_guest_has_fxsr(struct x86_emulate_ctxt *ctxt)
+{
+	return guest_cpuid_has(emul_to_vcpu(ctxt), X86_FEATURE_FXSR);
+}
+
 static ulong emulator_read_gpr(struct x86_emulate_ctxt *ctxt, unsigned reg)
 {
 	return kvm_register_read(emul_to_vcpu(ctxt), reg);
@@ -6322,6 +6337,9 @@ static const struct x86_emulate_ops emulate_ops = {
 	.fix_hypercall       = emulator_fix_hypercall,
 	.intercept           = emulator_intercept,
 	.get_cpuid           = emulator_get_cpuid,
+	.guest_has_long_mode = emulator_guest_has_long_mode,
+	.guest_has_movbe     = emulator_guest_has_movbe,
+	.guest_has_fxsr      = emulator_guest_has_fxsr,
 	.set_nmi_mask        = emulator_set_nmi_mask,
 	.get_hflags          = emulator_get_hflags,
 	.set_hflags          = emulator_set_hflags,