KVM: selftests: Add helpers to read kvm_{intel,amd} boolean module parameters

Add helper functions for reading the value of kvm_intel and kvm_amd
boolean module parameters. Use the kvm_intel variant in
vm_is_unrestricted_guest() to simplify the check for
kvm_intel.unrestricted_guest.

No functional change intended.
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220929181207.2281449-3-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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

@@ -175,6 +175,10 @@ extern const struct vm_guest_mode_params vm_guest_mode_params[];
 
 int open_path_or_exit(const char *path, int flags);
 int open_kvm_dev_path_or_exit(void);
+
+bool get_kvm_intel_param_bool(const char *param);
+bool get_kvm_amd_param_bool(const char *param);
+
 unsigned int kvm_check_cap(long cap);
 
 static inline bool kvm_has_cap(long cap)

tools/testing/selftests/kvm/lib/kvm_util.c

@@ -50,6 +50,45 @@ int open_kvm_dev_path_or_exit(void)
 	return _open_kvm_dev_path_or_exit(O_RDONLY);
 }
 
+static bool get_module_param_bool(const char *module_name, const char *param)
+{
+	const int path_size = 128;
+	char path[path_size];
+	char value;
+	ssize_t r;
+	int fd;
+
+	r = snprintf(path, path_size, "/sys/module/%s/parameters/%s",
+		     module_name, param);
+	TEST_ASSERT(r < path_size,
+		    "Failed to construct sysfs path in %d bytes.", path_size);
+
+	fd = open_path_or_exit(path, O_RDONLY);
+
+	r = read(fd, &value, 1);
+	TEST_ASSERT(r == 1, "read(%s) failed", path);
+
+	r = close(fd);
+	TEST_ASSERT(!r, "close(%s) failed", path);
+
+	if (value == 'Y')
+		return true;
+	else if (value == 'N')
+		return false;
+
+	TEST_FAIL("Unrecognized value '%c' for boolean module param", value);
+}
+
+bool get_kvm_intel_param_bool(const char *param)
+{
+	return get_module_param_bool("kvm_intel", param);
+}
+
+bool get_kvm_amd_param_bool(const char *param)
+{
+	return get_module_param_bool("kvm_amd", param);
+}
+
 /*
  * Capability
  *

tools/testing/selftests/kvm/lib/x86_64/processor.c

@@ -1294,20 +1294,9 @@ unsigned long vm_compute_max_gfn(struct kvm_vm *vm)
 /* Returns true if kvm_intel was loaded with unrestricted_guest=1. */
 bool vm_is_unrestricted_guest(struct kvm_vm *vm)
 {
-	char val = 'N';
-	size_t count;
-	FILE *f;
-
 	/* Ensure that a KVM vendor-specific module is loaded. */
 	if (vm == NULL)
 		close(open_kvm_dev_path_or_exit());
 
-	f = fopen("/sys/module/kvm_intel/parameters/unrestricted_guest", "r");
-	if (f) {
-		count = fread(&val, sizeof(char), 1, f);
-		TEST_ASSERT(count == 1, "Unable to read from param file.");
-		fclose(f);
-	}
-
-	return val == 'Y';
+	return get_kvm_intel_param_bool("unrestricted_guest");
 }