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Howlett" , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Muchun Song , Nikita Kalyazin , Oscar Salvador , Paolo Bonzini , Peter Xu , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH RFC 17/17] KVM: selftests: test userfaultfd missing for guest_memfd Date: Tue, 27 Jan 2026 21:29:36 +0200 Message-ID: <20260127192936.1250096-18-rppt@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260127192936.1250096-1-rppt@kernel.org> References: <20260127192936.1250096-1-rppt@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Stat-Signature: eo5mce1911yrjn1tp88mp7jnmu693j8z X-Rspamd-Queue-Id: 21427C0008 X-Rspam-User: X-HE-Tag: 1769542294-404424 X-HE-Meta: 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 eeX95fqk cjYKFOr1bwgOlJQnCmB2NfSlif2wiTiFKGQ5G6OpU1HczjhPJo6r0CKj/Ri4tGZ/f1G6IEpc0kCgyhGoggrr3h6DbTIK9aNM5nXjsHg4xNBMJre9LARpLI9TKWH09Rhh+O3PrEIiDJQu/v65yHCbneaVX6E3HxJUTxHfht6SK1Cqewcpo8doKhzMIUwgEKlMC9/Y8o9fw75fdF5RriZWvpmHsdJdzwkeI3N7yHNh64f7HgCoeHsMq7Ikg/MKv9ApmbLHWg3ulN4d1uAo1D68i8nADHGf9TKMSHkMX+UoPYoBfxIQ= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Nikita Kalyazin The test demonstrates that a missing userfaultfd event in guest_memfd can be resolved via a UFFDIO_COPY ioctl. Signed-off-by: Nikita Kalyazin Signed-off-by: Mike Rapoport (Microsoft) --- .../testing/selftests/kvm/guest_memfd_test.c | 80 ++++++++++++++++++- 1 file changed, 79 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c index 7612819e340a..f77e70d22175 100644 --- a/tools/testing/selftests/kvm/guest_memfd_test.c +++ b/tools/testing/selftests/kvm/guest_memfd_test.c @@ -439,6 +439,82 @@ static void test_uffd_minor(int fd, size_t total_size) close(uffd); } +static void test_uffd_missing(int fd, size_t total_size) +{ + struct uffdio_register uffd_reg; + struct uffdio_copy uffd_copy; + struct uffd_msg msg; + struct fault_args args; + pthread_t fault_thread; + void *mem, *buf = NULL; + int uffd, ret; + off_t offset = page_size; + void *fault_addr; + const char test_val = 0xab; + + ret = posix_memalign(&buf, page_size, total_size); + TEST_ASSERT_EQ(ret, 0); + memset(buf, test_val, total_size); + + uffd = syscall(__NR_userfaultfd, O_CLOEXEC); + TEST_ASSERT(uffd != -1, "userfaultfd creation should succeed"); + + struct uffdio_api uffdio_api = { + .api = UFFD_API, + .features = 0, + }; + ret = ioctl(uffd, UFFDIO_API, &uffdio_api); + TEST_ASSERT(ret != -1, "ioctl(UFFDIO_API) should succeed"); + + mem = mmap(NULL, total_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + TEST_ASSERT(mem != MAP_FAILED, "mmap should succeed"); + + uffd_reg.range.start = (unsigned long)mem; + uffd_reg.range.len = total_size; + uffd_reg.mode = UFFDIO_REGISTER_MODE_MISSING; + ret = ioctl(uffd, UFFDIO_REGISTER, &uffd_reg); + TEST_ASSERT(ret != -1, "ioctl(UFFDIO_REGISTER) should succeed"); + + fault_addr = mem + offset; + args.addr = fault_addr; + + ret = pthread_create(&fault_thread, NULL, fault_thread_fn, &args); + TEST_ASSERT(ret == 0, "pthread_create should succeed"); + + ret = read(uffd, &msg, sizeof(msg)); + TEST_ASSERT(ret != -1, "read from userfaultfd should succeed"); + TEST_ASSERT(msg.event == UFFD_EVENT_PAGEFAULT, "event type should be pagefault"); + TEST_ASSERT((void *)(msg.arg.pagefault.address & ~(page_size - 1)) == fault_addr, + "pagefault should occur at expected address"); + TEST_ASSERT(!(msg.arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WP), + "pagefault should not be write-protect"); + + uffd_copy.dst = (unsigned long)fault_addr; + uffd_copy.src = (unsigned long)(buf + offset); + uffd_copy.len = page_size; + uffd_copy.mode = 0; + ret = ioctl(uffd, UFFDIO_COPY, &uffd_copy); + TEST_ASSERT(ret != -1, "ioctl(UFFDIO_COPY) should succeed"); + + /* Wait for the faulting thread to complete - this provides the memory barrier */ + ret = pthread_join(fault_thread, NULL); + TEST_ASSERT(ret == 0, "pthread_join should succeed"); + + /* + * Now it's safe to check args.value - the thread has completed + * and memory is synchronized + */ + TEST_ASSERT(args.value == test_val, + "memory should contain the value that was copied"); + TEST_ASSERT(*(char *)(mem + offset) == test_val, + "no further fault is expected"); + + ret = munmap(mem, total_size); + TEST_ASSERT(!ret, "munmap should succeed"); + free(buf); + close(uffd); +} + static void test_guest_memfd_flags(struct kvm_vm *vm) { uint64_t valid_flags = vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_FLAGS); @@ -494,8 +570,10 @@ static void __test_guest_memfd(struct kvm_vm *vm, uint64_t flags) gmem_test(fallocate, vm, flags); gmem_test(invalid_punch_hole, vm, flags); - if (flags & GUEST_MEMFD_FLAG_INIT_SHARED) + if (flags & GUEST_MEMFD_FLAG_INIT_SHARED) { gmem_test(uffd_minor, vm, flags); + gmem_test(uffd_missing, vm, flags); + } } static void test_guest_memfd(unsigned long vm_type) -- 2.51.0