KVM: x86 emulator: change ->get_cpuid() accessor to use the x86 semantics

Instead of getting an exact leaf, follow the spec and fall back to the last
main leaf instead.  This lets us easily emulate the cpuid instruction in the
emulator.
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/include/asm/kvm_emulate.h

@@ -192,8 +192,8 @@ struct x86_emulate_ops {
 			 struct x86_instruction_info *info,
 			 enum x86_intercept_stage stage);
 
-	bool (*get_cpuid)(struct x86_emulate_ctxt *ctxt,
-			 u32 *eax, u32 *ebx, u32 *ecx, u32 *edx);
+	void (*get_cpuid)(struct x86_emulate_ctxt *ctxt,
+			  u32 *eax, u32 *ebx, u32 *ecx, u32 *edx);
 };
 
 typedef u32 __attribute__((vector_size(16))) sse128_t;

arch/x86/kvm/emulate.c

@@ -1993,8 +1993,8 @@ static bool vendor_intel(struct x86_emulate_ctxt *ctxt)
 	u32 eax, ebx, ecx, edx;
 
 	eax = ecx = 0;
-	return ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx)
-		&& ebx == X86EMUL_CPUID_VENDOR_GenuineIntel_ebx
+	ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx);
+	return ebx == X86EMUL_CPUID_VENDOR_GenuineIntel_ebx
 		&& ecx == X86EMUL_CPUID_VENDOR_GenuineIntel_ecx
 		&& edx == X86EMUL_CPUID_VENDOR_GenuineIntel_edx;
 }
@@ -2013,32 +2013,31 @@ static bool em_syscall_is_enabled(struct x86_emulate_ctxt *ctxt)
 
 	eax = 0x00000000;
 	ecx = 0x00000000;
-	if (ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx)) {
-		/*
-		 * Intel ("GenuineIntel")
-		 * remark: Intel CPUs only support "syscall" in 64bit
-		 * longmode. Also an 64bit guest with a
-		 * 32bit compat-app running will #UD !! While this
-		 * behaviour can be fixed (by emulating) into AMD
-		 * response - CPUs of AMD can't behave like Intel.
-		 */
-		if (ebx == X86EMUL_CPUID_VENDOR_GenuineIntel_ebx &&
-		    ecx == X86EMUL_CPUID_VENDOR_GenuineIntel_ecx &&
-		    edx == X86EMUL_CPUID_VENDOR_GenuineIntel_edx)
-			return false;
+	ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx);
+	/*
+	 * Intel ("GenuineIntel")
+	 * remark: Intel CPUs only support "syscall" in 64bit
+	 * longmode. Also an 64bit guest with a
+	 * 32bit compat-app running will #UD !! While this
+	 * behaviour can be fixed (by emulating) into AMD
+	 * response - CPUs of AMD can't behave like Intel.
+	 */
+	if (ebx == X86EMUL_CPUID_VENDOR_GenuineIntel_ebx &&
+	    ecx == X86EMUL_CPUID_VENDOR_GenuineIntel_ecx &&
+	    edx == X86EMUL_CPUID_VENDOR_GenuineIntel_edx)
+		return false;
 
-		/* AMD ("AuthenticAMD") */
-		if (ebx == X86EMUL_CPUID_VENDOR_AuthenticAMD_ebx &&
-		    ecx == X86EMUL_CPUID_VENDOR_AuthenticAMD_ecx &&
-		    edx == X86EMUL_CPUID_VENDOR_AuthenticAMD_edx)
-			return true;
-
-		/* AMD ("AMDisbetter!") */
-		if (ebx == X86EMUL_CPUID_VENDOR_AMDisbetterI_ebx &&
-		    ecx == X86EMUL_CPUID_VENDOR_AMDisbetterI_ecx &&
-		    edx == X86EMUL_CPUID_VENDOR_AMDisbetterI_edx)
-			return true;
-	}
+	/* AMD ("AuthenticAMD") */
+	if (ebx == X86EMUL_CPUID_VENDOR_AuthenticAMD_ebx &&
+	    ecx == X86EMUL_CPUID_VENDOR_AuthenticAMD_ecx &&
+	    edx == X86EMUL_CPUID_VENDOR_AuthenticAMD_edx)
+		return true;
+
+	/* AMD ("AMDisbetter!") */
+	if (ebx == X86EMUL_CPUID_VENDOR_AMDisbetterI_ebx &&
+	    ecx == X86EMUL_CPUID_VENDOR_AMDisbetterI_ecx &&
+	    edx == X86EMUL_CPUID_VENDOR_AMDisbetterI_edx)
+		return true;
 
 	/* default: (not Intel, not AMD), apply Intel's stricter rules... */
 	return false;

arch/x86/kvm/x86.c

@@ -4302,26 +4302,10 @@ static int emulator_intercept(struct x86_emulate_ctxt *ctxt,
 	return kvm_x86_ops->check_intercept(emul_to_vcpu(ctxt), info, stage);
 }
 
-static bool emulator_get_cpuid(struct x86_emulate_ctxt *ctxt,
+static void emulator_get_cpuid(struct x86_emulate_ctxt *ctxt,
 			       u32 *eax, u32 *ebx, u32 *ecx, u32 *edx)
 {
-	struct kvm_cpuid_entry2 *cpuid = NULL;
-
-	if (eax && ecx)
-		cpuid = kvm_find_cpuid_entry(emul_to_vcpu(ctxt),
-					    *eax, *ecx);
-
-	if (cpuid) {
-		*eax = cpuid->eax;
-		*ecx = cpuid->ecx;
-		if (ebx)
-			*ebx = cpuid->ebx;
-		if (edx)
-			*edx = cpuid->edx;
-		return true;
-	}
-
-	return false;
+	kvm_cpuid(emul_to_vcpu(ctxt), eax, ebx, ecx, edx);
 }
 
 static struct x86_emulate_ops emulate_ops = {