[PATCH v3] KVM: selftests: Add a test for KVM_CREATE_VM VM type enforcement

[Hemanth Selam <hemanth.selam@gmail.com>]

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>
---
Changes in v3:
 - Reworked into a separate, generic test that checks all VM types
   against KVM_CAP_VM_TYPES (per review), instead of adding negative
   checks to sev_init2_tests; also cover out-of-range types. Dropped the
   manual fd cleanup and the redundant errno in the assert message, and
   removed the addressed TODO from sev_init2_tests.c.
 - Dropped the separate "SEV: Sanity check the launch measurement" patch
   that accompanied v1/v2; this revision is a single patch.

v2: https://lore.kernel.org/all/20260709174955.628913-1-hemanth.selam@gmail.com/
v1: https://lore.kernel.org/all/20260709164751.621326-1-hemanth.selam@gmail.com/

 tools/testing/selftests/kvm/Makefile.kvm      |  1 +
 tools/testing/selftests/kvm/vm_types_test.c   | 50 +++++++++++++++++++
 .../selftests/kvm/x86/sev_init2_tests.c       |  4 --
 3 files changed, 51 insertions(+), 4 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/vm_types_test.c

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index d28a057fa6c2..ad74d0b98694 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/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)
diff --git a/tools/testing/selftests/kvm/vm_types_test.c b/tools/testing/selftests/kvm/vm_types_test.c
new file mode 100644
index 000000000000..e8ef3b018f6c
--- /dev/null
+++ b/tools/testing/selftests/kvm/vm_types_test.c
@@ -0,0 +1,50 @@
+// 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 int supported_types;
+	unsigned long type;
+	int kvm_fd, 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("KVM_CAP_VM_TYPES: 0x%x\n", supported_types);
+
+	/*
+	 * KVM_CAP_VM_TYPES is a u32 bitmap, so only types 0..31 can ever be
+	 * advertised.  Walk past that range as well to confirm that any
+	 * out-of-range type is rejected rather than silently accepted.
+	 */
+	for (type = 0; type < 64; type++) {
+		bool supported = type < 32 && (supported_types & (1U << type));
+
+		fd = __kvm_ioctl(kvm_fd, KVM_CREATE_VM, (void *)type);
+
+		if (supported) {
+			TEST_ASSERT(fd >= 0,
+				    "KVM_CREATE_VM(%lu) should succeed, KVM_CAP_VM_TYPES=0x%x",
+				    type, supported_types);
+			close(fd);
+		} else {
+			TEST_ASSERT(fd < 0 && errno == EINVAL,
+				    "KVM_CREATE_VM(%lu) should fail with EINVAL, KVM_CAP_VM_TYPES=0x%x",
+				    type, supported_types);
+		}
+	}
+
+	return 0;
+}
diff --git a/tools/testing/selftests/kvm/x86/sev_init2_tests.c b/tools/testing/selftests/kvm/x86/sev_init2_tests.c
index 8db88c355f16..d4227dc922ab 100644
--- a/tools/testing/selftests/kvm/x86/sev_init2_tests.c
+++ b/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){});
 
-- 
2.43.7