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Howlett" , Lorenzo Stoakes , "Matthew Wilcox (Oracle)" , Michal Hocko , Mike Rapoport , Muchun Song , Nikita Kalyazin , Oscar Salvador , Paolo Bonzini , Peter Xu , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , kvm@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v2 15/15] KVM: selftests: test userfaultfd missing for guest_memfd Date: Fri, 6 Mar 2026 19:18:15 +0200 Message-ID: <20260306171815.3160826-16-rppt@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260306171815.3160826-1-rppt@kernel.org> References: <20260306171815.3160826-1-rppt@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: x4z7mmnrkg9qc6fkkpan33f9wnh1jxbu X-Rspam-User: X-Rspamd-Queue-Id: 6D6481C0007 X-Rspamd-Server: rspam12 X-HE-Tag: 1772817600-790158 X-HE-Meta: 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 D2zeTwUz zroXQmOmLYVK41/M1K2uStLGkMR4eTsJD53JeCEgw6F0SYAySPWhyi5HpY6IUvjypkdTnVzVQpQw08OVBtd1I3MV5NTXGN6h3OpggKeDjqcSob2wrnCkOB5eHL+HVHBQ4c3eWj4JXZyEzmNu6KCDEC7dHQgUcw6f186j7E7juwsFVA5WSfs3oInK2HXVuK9g4vrGg6PPfWprA4TMTdg7xBFAj4/0AGxsm6A86dO35ZBRaYeBuPPiPww5rLGjerra7zqCsEa1vZBE1uyUzVghu7/DZi5TCcTvInFejtscwR7hhY53StwTI67NAtA== 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