KVM: selftests: Add memory size parameter to the demand paging test

Add an argument to allow the demand paging test to work on larger and
smaller guest sizes.

Signed-off-by: Ben Gardon <bgardon@google.com>
[Rewrote parse_size() to simplify and provide user more flexibility as
 to how sizes are input. Also fixed size overflow assert.]
Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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

@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * tools/testing/selftests/kvm/lib/test_util.c
+ *
+ * Copyright (C) 2020, Google LLC.
+ */
+#include <stdlib.h>
+#include <ctype.h>
+#include <limits.h>
+#include "test_util.h"
+
+/*
+ * Parses "[0-9]+[kmgt]?".
+ */
+size_t parse_size(const char *size)
+{
+	size_t base;
+	char *scale;
+	int shift = 0;
+
+	TEST_ASSERT(size && isdigit(size[0]), "Need at least one digit in '%s'", size);
+
+	base = strtoull(size, &scale, 0);
+
+	TEST_ASSERT(base != ULLONG_MAX, "Overflow parsing size!");
+
+	switch (tolower(*scale)) {
+	case 't':
+		shift = 40;
+		break;
+	case 'g':
+		shift = 30;
+		break;
+	case 'm':
+		shift = 20;
+		break;
+	case 'k':
+		shift = 10;
+		break;
+	case 'b':
+	case '\0':
+		shift = 0;
+		break;
+	default:
+		TEST_ASSERT(false, "Unknown size letter %c", *scale);
+	}
+
+	TEST_ASSERT((base << shift) >> shift == base, "Overflow scaling size!");
+
+	return base << shift;
+}