KVM: selftests: Add a test for KVM_CREATE_VM VM type enforcement

KVM_CAP_VM_TYPES advertises the bitmap of VM types that KVM_CREATE_VM
accepts, but nothing verified that the ioctl actually enforces it: that
every advertised type can be created and every non-advertised type is
rejected. sev_init2_tests carried a TODO for this ("check that
unsupported types cannot be created. Probably a separate selftest"),
but the check is not specific to SEV or KVM_SEV_INIT2, and not even to
x86.

Add a standalone test that walks the type space and, for each value,
asserts that KVM_CREATE_VM succeeds iff the corresponding bit is set in
KVM_CAP_VM_TYPES, and otherwise fails with -EINVAL. The walk extends
past bit 31 so that out-of-range type values, which can never be
advertised in the u32 bitmap, are also confirmed to be rejected. The
test only depends on KVM_CAP_VM_TYPES, so it lives in the common set and
is skipped on architectures that don't advertise the capability.

Drop the now-addressed TODO from sev_init2_tests.c.

Tested on an AMD SEV-SNP capable host. With KVM_CAP_VM_TYPES=0x15
(DEFAULT/SEV/SNP), only the advertised types are created and everything
else is rejected:

  $ strace -e trace=ioctl ./vm_types_test 2>&1 | grep KVM_CREATE_VM
  ioctl(3, KVM_CREATE_VM, 0)    = 4              # DEFAULT
  ioctl(3, KVM_CREATE_VM, 0x1)  = -1 EINVAL      # SW_PROTECTED
  ioctl(3, KVM_CREATE_VM, 0x2)  = 4              # SEV
  ioctl(3, KVM_CREATE_VM, 0x3)  = -1 EINVAL      # SEV-ES
  ioctl(3, KVM_CREATE_VM, 0x4)  = 4              # SNP
  ioctl(3, KVM_CREATE_VM, 0x5)  = -1 EINVAL      # TDX
  ... 0x6..0x3f all -1 EINVAL ...

Reloading kvm_amd with sev_snp=0 drops the bitmap to 0x5 and only types
0 and 2 are then created, confirming the test tracks the advertised set
rather than hard-coded types.

Signed-off-by: Hemanth Selam <hemanth.selam@gmail.com>
Link: https://patch.msgid.link/20260710050442.826777-1-hemanth.selam@gmail.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

tools/testing/selftests/kvm/Makefile.kvm

@@ -66,6 +66,7 @@ TEST_GEN_PROGS_COMMON += kvm_page_table_test
 TEST_GEN_PROGS_COMMON += set_memory_region_test
 TEST_GEN_PROGS_COMMON += memslot_modification_stress_test
 TEST_GEN_PROGS_COMMON += memslot_perf_test
+TEST_GEN_PROGS_COMMON += vm_types_test
 
 # Compiled test targets
 TEST_GEN_PROGS_x86 = $(TEST_GEN_PROGS_COMMON)

tools/testing/selftests/kvm/vm_types_test.c

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Verify that KVM_CREATE_VM accepts exactly the VM types enumerated by
+ * KVM_CAP_VM_TYPES, and rejects every other type with -EINVAL.
+ */
+#include <errno.h>
+#include <stdbool.h>
+#include <unistd.h>
+
+#include <linux/kvm.h>
+
+#include "kvm_util.h"
+#include "test_util.h"
+
+int main(void)
+{
+	unsigned long type, supported_types;
+	int kvm_fd;
+
+	TEST_REQUIRE(kvm_has_cap(KVM_CAP_VM_TYPES));
+
+	kvm_fd = open_kvm_dev_path_or_exit();
+	supported_types = kvm_check_cap(KVM_CAP_VM_TYPES);
+	pr_info("Supported VM types: 0x%lx\n", supported_types);
+
+	/*
+	 * For compatibility with 32-bit kernels, KVM_CHECK_EXTENSION restricts
+	 * its return to 32-bit values, i.e. only types 0..31 can be advertised.
+	 * Walk past that range as well to confirm that any out-of-range type is
+	 * rejected rather than silently accepted (or truncated).
+	 */
+	for (type = 0; type < BITS_PER_TYPE(supported_types); type++) {
+		int fd = __kvm_ioctl(kvm_fd, KVM_CREATE_VM, (void *)type);
+
+		if (supported_types & BIT(type)) {
+			TEST_ASSERT(fd >= 0,
+				    "KVM_CREATE_VM(%lu) should succeed, supported types = 0x%lx",
+				    type, supported_types);
+			kvm_close(fd);
+		} else {
+			TEST_ASSERT(fd < 0 && errno == EINVAL,
+				    "KVM_CREATE_VM(%lu) should fail with EINVAL, supported types = 0x%lx",
+				    type, supported_types);
+		}
+	}
+
+	return 0;
+}

tools/testing/selftests/kvm/x86/sev_init2_tests.c

@@ -77,10 +77,6 @@ void test_vm_types(void)
 {
 	test_init2(KVM_X86_SEV_VM, &(struct kvm_sev_init){});
 
-	/*
-	 * TODO: check that unsupported types cannot be created.  Probably
-	 * a separate selftest.
-	 */
 	if (have_sev_es)
 		test_init2(KVM_X86_SEV_ES_VM, &(struct kvm_sev_init){});