KVM: selftests: Add SMT control state helper

Move the SMT control check out of the hyperv_cpuid selftest so that it
is generally accessible all KVM selftests. Split the functionality into
a helper that populates a buffer with SMT control value which other
helpers can use to ascertain if SMT state is available and active.

Signed-off-by: Pratik R. Sampat <prsampat@amd.com>
Link: https://lore.kernel.org/r/20250305230000.231025-5-prsampat@amd.com
[sean: prepend is_ to the helpers]
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: pratiksampat

tools/testing/selftests/kvm/include/kvm_util.h

@@ -549,6 +549,41 @@ void kvm_get_stat(struct kvm_binary_stats *stats, const char *name,
 #define vm_get_stat(vm, stat) __get_stat(&(vm)->stats, stat)
 #define vcpu_get_stat(vcpu, stat) __get_stat(&(vcpu)->stats, stat)
 
+static inline bool read_smt_control(char *buf, size_t buf_size)
+{
+	FILE *f = fopen("/sys/devices/system/cpu/smt/control", "r");
+	bool ret;
+
+	if (!f)
+		return false;
+
+	ret = fread(buf, sizeof(*buf), buf_size, f) > 0;
+	fclose(f);
+
+	return ret;
+}
+
+static inline bool is_smt_possible(void)
+{
+	char buf[16];
+
+	if (read_smt_control(buf, sizeof(buf)) &&
+	    (!strncmp(buf, "forceoff", 8) || !strncmp(buf, "notsupported", 12)))
+		return false;
+
+	return true;
+}
+
+static inline bool is_smt_on(void)
+{
+	char buf[16];
+
+	if (read_smt_control(buf, sizeof(buf)) && !strncmp(buf, "on", 2))
+		return true;
+
+	return false;
+}
+
 void vm_create_irqchip(struct kvm_vm *vm);
 
 static inline int __vm_create_guest_memfd(struct kvm_vm *vm, uint64_t size,

tools/testing/selftests/kvm/x86/hyperv_cpuid.c

@@ -22,25 +22,6 @@ static void guest_code(void)
 {
 }
 
-static bool smt_possible(void)
-{
-	char buf[16];
-	FILE *f;
-	bool res = true;
-
-	f = fopen("/sys/devices/system/cpu/smt/control", "r");
-	if (f) {
-		if (fread(buf, sizeof(*buf), sizeof(buf), f) > 0) {
-			if (!strncmp(buf, "forceoff", 8) ||
-			    !strncmp(buf, "notsupported", 12))
-				res = false;
-		}
-		fclose(f);
-	}
-
-	return res;
-}
-
 static void test_hv_cpuid(struct kvm_vcpu *vcpu, bool evmcs_expected)
 {
 	const bool has_irqchip = !vcpu || vcpu->vm->has_irqchip;
@@ -93,7 +74,7 @@ static void test_hv_cpuid(struct kvm_vcpu *vcpu, bool evmcs_expected)
 		case 0x40000004:
 			test_val = entry->eax & (1UL << 18);
 
-			TEST_ASSERT(!!test_val == !smt_possible(),
+			TEST_ASSERT(!!test_val == !is_smt_possible(),
 				    "NoNonArchitecturalCoreSharing bit"
 				    " doesn't reflect SMT setting");