[RFC PATCH v1 35/37] KVM: selftests: Add script to exercise private_mem_conversions_test

[Ackerley Tng <ackerleytng@google.com>]

Add a wrapper script to simplify running the private_mem_conversions_test
with a variety of configurations. Manually invoking the test for all
supported memory backing source types is tedious.

The script automatically detects the availability of 2MB and 1GB hugepages
and builds a list of source types to test. It then iterates through the
list, running the test for each type with both a single memslot and
multiple memslots.

This makes it easier to get comprehensive test coverage across different
memory configurations.

Use python to be able to issue an ioctl to /dev/kvm.

Update .gitignore to allowlist python scripts.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
 tools/testing/selftests/kvm/.gitignore        |   1 +
 .../kvm/x86/private_mem_conversions_test.py   | 159 ++++++++++++++++++
 2 files changed, 160 insertions(+)
 create mode 100755 tools/testing/selftests/kvm/x86/private_mem_conversions_test.py

diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore
index 1d41a046a7bfd..d7e9c1d97e376 100644
--- a/tools/testing/selftests/kvm/.gitignore
+++ b/tools/testing/selftests/kvm/.gitignore
@@ -4,6 +4,7 @@
 !*.c
 !*.h
 !*.S
+!*.py
 !*.sh
 !.gitignore
 !config
diff --git a/tools/testing/selftests/kvm/x86/private_mem_conversions_test.py b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.py
new file mode 100755
index 0000000000000..32421ae824d64
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.py
@@ -0,0 +1,159 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Wrapper script which runs different test setups of
+# private_mem_conversions_test.
+#
+# Copyright (C) 2025, Google LLC.
+
+import os
+import fcntl
+import sys
+import subprocess
+
+
+NUM_VCPUS_TO_TEST = 4
+NUM_MEMSLOTS_TO_TEST = NUM_VCPUS_TO_TEST
+
+# Required pages are based on the test setup in the C code.
+# These static requirements are set to the maximum required for
+# NUM_VCPUS_TO_TEST, over all the hugetlb-related tests
+REQUIRED_NUM_2M_HUGEPAGES = 1024 * NUM_VCPUS_TO_TEST
+REQUIRED_NUM_1G_HUGEPAGES = 2 * NUM_VCPUS_TO_TEST
+
+
+def get_hugepage_count(page_size_kb: int) -> int:
+    """Reads the current number of hugepages available for a given size."""
+    try:
+        path = f"/sys/kernel/mm/hugepages/hugepages-{page_size_kb}kB/nr_hugepages"
+        with open(path, 'r') as f:
+            return int(f.read().strip())
+    except (FileNotFoundError, ValueError):
+        return 0
+
+
+def get_default_hugepage_size_in_kb():
+    """Reads the default hugepage size from /proc/meminfo."""
+    try:
+        with open("/proc/meminfo", 'r') as f:
+            for line in f:
+                if line.startswith("Hugepagesize:"):
+                    parts = line.split()
+                    if len(parts) >= 2 and parts[1].isdigit():
+                        return int(parts[1])
+    except FileNotFoundError:
+        return None
+
+
+def run_tests(executable_path: str, src_type: str, num_memslots: int, num_vcpus: int) -> None:
+    """Runs the test executable with different arguments."""
+    print(f"Running tests for backing source type: {src_type}")
+
+    command1 = [executable_path, "-s", src_type, "-m", str(num_memslots)]
+    print(" ".join(command1))
+    _ = subprocess.run(command1, check=True)
+
+    command2 = [executable_path, "-s", src_type, "-m", str(num_memslots), "-n", str(num_vcpus)]
+    print(" ".join(command2))
+    _ = subprocess.run(command2, check=True)
+
+
+def kvm_check_cap(capability: int) -> int:
+    KVM_CHECK_EXTENSION = 0xAE03
+    KVM_DEVICE = '/dev/kvm'
+
+    if not os.path.exists(KVM_DEVICE):
+        print(f"Error: KVM device not found at {KVM_DEVICE}. Is the 'kvm' module loaded?")
+        return -1
+
+    try:
+        fd = os.open(KVM_DEVICE, os.O_RDWR)
+
+        # Issue the ioctl: fcntl.ioctl(fd, request, arg)
+        # request is KVM_CHECK_EXTENSION (0xAE03)
+        # arg is the capability constant (e.g., KVM_CAP_COALESCED_MMIO)
+        result = fcntl.ioctl(fd, KVM_CHECK_EXTENSION, capability)
+
+        os.close(fd)
+        return result
+    except OSError as e:
+        print(f"Error issuing KVM ioctl on {KVM_DEVICE}: {e}", file=sys.stderr)
+        if fd > 0:
+            os.close(fd)
+        return -1
+
+
+def kvm_has_gmem_attributes() -> bool:
+    KVM_CAP_GUEST_MEMFD_MEMORY_ATTRIBUTES = 245
+
+    return kvm_check_cap(KVM_CAP_GUEST_MEMFD_MEMORY_ATTRIBUTES) > 0
+
+
+def get_backing_source_types() -> list[str]:
+    hugepage_2mb_count = get_hugepage_count(2048)
+    hugepage_2mb_enabled = hugepage_2mb_count >= REQUIRED_NUM_2M_HUGEPAGES
+    hugepage_1gb_count = get_hugepage_count(1048576)
+    hugepage_1gb_enabled = hugepage_1gb_count >= REQUIRED_NUM_1G_HUGEPAGES
+
+    default_hugepage_size_kb = get_default_hugepage_size_in_kb()
+    hugepage_default_enabled = False
+    if default_hugepage_size_kb == 2048:
+        hugepage_default_enabled = hugepage_2mb_enabled
+    elif default_hugepage_size_kb == 1048576:
+        hugepage_default_enabled = hugepage_1gb_enabled
+
+    backing_src_types: list[str] = ["anonymous", "anonymous_thp"]
+
+    if hugepage_default_enabled:
+        backing_src_types.append("anonymous_hugetlb")
+    else:
+        print("skipping anonymous_hugetlb backing source type")
+
+    if hugepage_2mb_enabled:
+        backing_src_types.append("anonymous_hugetlb_2mb")
+    else:
+        print("skipping anonymous_hugetlb_2mb backing source type")
+
+    if hugepage_1gb_enabled:
+        backing_src_types.append("anonymous_hugetlb_1gb")
+    else:
+        print("skipping anonymous_hugetlb_1gb backing source type")
+
+    backing_src_types.append("shmem")
+
+    if hugepage_default_enabled:
+        backing_src_types.append("shared_hugetlb")
+    else:
+        print("skipping shared_hugetlb backing source type")
+
+    return backing_src_types
+
+
+def main():
+    script_dir = os.path.dirname(os.path.abspath(__file__))
+    test_executable = os.path.join(script_dir, "private_mem_conversions_test")
+
+    if not os.path.exists(test_executable):
+        print(f"Error: Test executable not found at '{test_executable}'", file=sys.stderr)
+        sys.exit(1)
+
+    return_code = 0
+
+    backing_src_types = ["shmem"] if kvm_has_gmem_attributes() else get_backing_source_types()
+    try:
+        for i, src_type in enumerate(backing_src_types):
+            if i > 0:
+                print()
+            run_tests(test_executable, src_type, NUM_MEMSLOTS_TO_TEST, NUM_VCPUS_TO_TEST)
+    except subprocess.CalledProcessError as e:
+        print(f"Test failed for source type '{src_type}'. Command: {' '.join(e.cmd)}", file=sys.stderr)
+        return_code = e.returncode
+    except Exception as e:
+        print(f"An unexpected error occurred: {e}", file=sys.stderr)
+        return_code = 1
+
+    sys.exit(return_code)
+
+
+if __name__ == "__main__":
+    main()
-- 
2.51.0.858.gf9c4a03a3a-goog