kernel/tools/testing/selftests/kvm/guest_memfd_test.c, branch linux-rolling-stable

KVM: selftests: Add guest_memfd tests for mmap and NUMA policy support

2025-10-20T13:30:45Z

Add tests for NUMA memory policy binding and NUMA aware allocation in guest_memfd. This extends the existing selftests by adding proper validation for: - KVM GMEM set_policy and get_policy() vm_ops functionality using mbind() and get_mempolicy() - NUMA policy application before and after memory allocation Run the NUMA mbind() test with and without INIT_SHARED, as KVM should allow doing mbind(), madvise(), etc. on guest-private memory, e.g. so that userspace can set NUMA policy for CoCo VMs. Run the NUMA allocation test only for INIT_SHARED, i.e. if the host can't fault-in memory (via direct access, madvise(), etc.) as move_pages() returns -ENOENT if the page hasn't been faulted in (walks the host page tables to find the associated folio) [sean: don't skip entire test when running on non-NUMA system, test mbind() with private memory, provide more info in assert messages] Signed-off-by: Shivank Garg Tested-by: Ashish Kalra Link: https://lore.kernel.org/r/20251016172853.52451-12-seanjc@google.com Signed-off-by: Sean Christopherson

KVM: selftests: Verify that reads to inaccessible guest_memfd VMAs SIGBUS

2025-10-10T21:25:30Z

Expand the guest_memfd negative testcases for overflow and MAP_PRIVATE to verify that reads to inaccessible memory also get a SIGBUS. Reviewed-by: Ackerley Tng Tested-by: Ackerley Tng Reviewed-by: Lisa Wang Tested-by: Lisa Wang Link: https://lore.kernel.org/r/20251003232606.4070510-14-seanjc@google.com Signed-off-by: Sean Christopherson

KVM: selftests: Verify that faulting in private guest_memfd memory fails

2025-10-10T21:25:30Z

Add a guest_memfd testcase to verify that faulting in private memory gets a SIGBUS. For now, test only the case where memory is private by default since KVM doesn't yet support in-place conversion. Deliberately run the CoW test with and without INIT_SHARED set as KVM should disallow MAP_PRIVATE regardless of whether the memory itself is private from a CoCo perspective. Cc: Ackerley Tng Reviewed-by: Fuad Tabba Tested-by: Fuad Tabba Reviewed-by: David Hildenbrand Reviewed-by: Ackerley Tng Tested-by: Ackerley Tng Link: https://lore.kernel.org/r/20251003232606.4070510-13-seanjc@google.com Signed-off-by: Sean Christopherson

KVM: selftests: Add wrapper macro to handle and assert on expected SIGBUS

2025-10-10T21:25:29Z

Extract the guest_memfd test's SIGBUS handling functionality into a common TEST_EXPECT_SIGBUS() macro in anticipation of adding more SIGBUS testcases. Eating a SIGBUS isn't terrible difficult, but it requires a non-trivial amount of boilerplate code, and using a macro allows selftests to print out the exact action that failed to generate a SIGBUS without the developer needing to remember to add a useful error message. Explicitly mark the SIGBUS handler as "used", as gcc-14 at least likes to discard the function before linking. Opportunistically use TEST_FAIL(...) instead of TEST_ASSERT(false, ...), and fix the write path of the guest_memfd test to use the local "val" instead of hardcoding the literal value a second time. Suggested-by: Ackerley Tng Reviewed-by: Ackerley Tng Tested-by: Ackerley Tng Reviewed-by: Lisa Wang Tested-by: Lisa Wang Link: https://lore.kernel.org/r/20251003232606.4070510-12-seanjc@google.com Signed-off-by: Sean Christopherson

KVM: selftests: Isolate the guest_memfd Copy-on-Write negative testcase

2025-10-10T21:25:28Z

Move the guest_memfd Copy-on-Write (CoW) testcase to its own function to better separate positive testcases from negative testcases. No functional change intended. Suggested-by: Ackerley Tng Reviewed-by: Ackerley Tng Tested-by: Ackerley Tng Link: https://lore.kernel.org/r/20251003232606.4070510-11-seanjc@google.com Signed-off-by: Sean Christopherson

KVM: selftests: Add wrappers for mmap() and munmap() to assert success

2025-10-10T21:25:28Z

Add and use wrappers for mmap() and munmap() that assert success to reduce a significant amount of boilerplate code, to ensure all tests assert on failure, and to provide consistent error messages on failure. No functional change intended. Reviewed-by: Fuad Tabba Tested-by: Fuad Tabba Reviewed-by: David Hildenbrand Reviewed-by: Ackerley Tng Link: https://lore.kernel.org/r/20251003232606.4070510-10-seanjc@google.com Signed-off-by: Sean Christopherson

KVM: selftests: Add test coverage for guest_memfd without GUEST_MEMFD_FLAG_MMAP

2025-10-10T21:25:27Z

If a VM type supports KVM_CAP_GUEST_MEMFD_MMAP, the guest_memfd test will run all test cases with GUEST_MEMFD_FLAG_MMAP set. This leaves the code path for creating a non-mmap()-able guest_memfd on a VM that supports mappable guest memfds untested. Refactor the test to run the main test suite with a given set of flags. Then, for VM types that support the mappable capability, invoke the test suite twice: once with no flags, and once with GUEST_MEMFD_FLAG_MMAP set. This ensures both creation paths are properly exercised on capable VMs. Run test_guest_memfd_flags() only once per VM type since it depends only on the set of valid/supported flags, i.e. iterating over an arbitrary set of flags is both unnecessary and wrong. Signed-off-by: Ackerley Tng [sean: use double-underscores for the inner helper] Reviewed-by: Fuad Tabba Tested-by: Fuad Tabba Reviewed-by: David Hildenbrand Link: https://lore.kernel.org/r/20251003232606.4070510-9-seanjc@google.com Signed-off-by: Sean Christopherson

KVM: selftests: Create a new guest_memfd for each testcase

2025-10-10T21:25:26Z

Refactor the guest_memfd selftest to improve test isolation by creating a a new guest_memfd for each testcase. Currently, the test reuses a single guest_memfd instance for all testcases, and thus creates dependencies between tests, e.g. not truncating folios from the guest_memfd instance at the end of a test could lead to unexpected results (see the PUNCH_HOLE purging that needs to done by in-flight the NUMA testcases[1]). Invoke each test via a macro wrapper to create and close a guest_memfd to cut down on the boilerplate copy+paste needed to create a test. Link: https://lore.kernel.org/all/20250827175247.83322-10-shivankg@amd.com Reported-by: Ackerley Tng Reviewed-by: Fuad Tabba Tested-by: Fuad Tabba Reviewed-by: David Hildenbrand Reviewed-by: Ackerley Tng Tested-by: Ackerley Tng Link: https://lore.kernel.org/r/20251003232606.4070510-8-seanjc@google.com Signed-off-by: Sean Christopherson

KVM: selftests: Stash the host page size in a global in the guest_memfd test

2025-10-10T21:25:26Z

Use a global variable to track the host page size in the guest_memfd test so that the information doesn't need to be constantly passed around. The state is purely a reflection of the underlying system, i.e. can't be set by the test and is constant for a given invocation of the test, and thus explicitly passing the host page size to individual testcases adds no value, e.g. doesn't allow testing different combinations. Making page_size a global will simplify an upcoming change to create a new guest_memfd instance per testcase. No functional change intended. Reviewed-by: Fuad Tabba Tested-by: Fuad Tabba Reviewed-by: David Hildenbrand Reviewed-by: Ackerley Tng Tested-by: Ackerley Tng Link: https://lore.kernel.org/r/20251003232606.4070510-7-seanjc@google.com Signed-off-by: Sean Christopherson

KVM: guest_memfd: Add INIT_SHARED flag, reject user page faults if not set

2025-10-10T21:25:23Z

Add a guest_memfd flag to allow userspace to state that the underlying memory should be configured to be initialized as shared, and reject user page faults if the guest_memfd instance's memory isn't shared. Because KVM doesn't yet support in-place private<=>shared conversions, all guest_memfd memory effectively follows the initial state. Alternatively, KVM could deduce the initial state based on MMAP, which for all intents and purposes is what KVM currently does. However, implicitly deriving the default state based on MMAP will result in a messy ABI when support for in-place conversions is added. For x86 CoCo VMs, which don't yet support MMAP, memory is currently private by default (otherwise the memory would be unusable). If MMAP implies memory is shared by default, then the default state for CoCo VMs will vary based on MMAP, and from userspace's perspective, will change when in-place conversion support is added. I.e. to maintain guest<=>host ABI, userspace would need to immediately convert all memory from shared=>private, which is both ugly and inefficient. The inefficiency could be avoided by adding a flag to state that memory is _private_ by default, irrespective of MMAP, but that would lead to an equally messy and hard to document ABI. Bite the bullet and immediately add a flag to control the default state so that the effective behavior is explicit and straightforward. Fixes: 3d3a04fad25a ("KVM: Allow and advertise support for host mmap() on guest_memfd files") Cc: David Hildenbrand Reviewed-by: Fuad Tabba Tested-by: Fuad Tabba Reviewed-by: Ackerley Tng Tested-by: Ackerley Tng Reviewed-by: David Hildenbrand Link: https://lore.kernel.org/r/20251003232606.4070510-3-seanjc@google.com Signed-off-by: Sean Christopherson