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Howlett" , "Lorenzo Stoakes (Oracle)" , "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 v3 14/15] KVM: selftests: test userfaultfd minor for guest_memfd Date: Mon, 30 Mar 2026 13:11:15 +0300 Message-ID: <20260330101116.1117699-15-rppt@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260330101116.1117699-1-rppt@kernel.org> References: <20260330101116.1117699-1-rppt@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: 4oyoaxo8et8n7zkh9d1dcbzo6m71wi5q X-Rspamd-Queue-Id: DDF00180011 X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1774865581-25012 X-HE-Meta: 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 1UdSL0vG 2Qm0McNIV7RdkiCTYIzS9eb+WNvF/L73PRgoGQsaRQHR23gzPOYAMfwWiyBGHw1lTXrABCkIfLG+lO8NEawK0WeiwdxjzsHs80OE6gA9922iMzaNe/R0V4LgnKsThLzNiMuG/EqOCPbJP2gRsbpVLy5mcT90Api2WuVaLgtldRcqwcYJiCSpeuqWKvxGKjRom5OJwV31rhkwJKOifkSrtA6BHU7TdYLpKi0mQSzlEoNqv1nOC3YfDP/Pq0LBo9UF2hVCFED7ArUvfUHTEB5J7TANQOYqmcDTTBsu/fp5Kn9KP31Uk1g3y/ze+dQ== 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 minor userfaultfd event in guest_memfd can be resolved via a memcpy followed by a UFFDIO_CONTINUE ioctl. Signed-off-by: Nikita Kalyazin Signed-off-by: Mike Rapoport (Microsoft) --- .../testing/selftests/kvm/guest_memfd_test.c | 113 ++++++++++++++++++ 1 file changed, 113 insertions(+) diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c index cc329b57ce2e..29f8d686c09f 100644 --- a/tools/testing/selftests/kvm/guest_memfd_test.c +++ b/tools/testing/selftests/kvm/guest_memfd_test.c @@ -10,13 +10,17 @@ #include #include #include +#include #include #include #include +#include #include #include #include +#include +#include #include "kvm_util.h" #include "numaif.h" @@ -329,6 +333,112 @@ static void test_create_guest_memfd_multiple(struct kvm_vm *vm) close(fd1); } +struct fault_args { + char *addr; + char value; +}; + +static void *fault_thread_fn(void *arg) +{ + struct fault_args *args = arg; + + /* Trigger page fault */ + args->value = *args->addr; + return NULL; +} + +static void test_uffd_minor(int fd, size_t total_size) +{ + struct uffdio_register uffd_reg; + struct uffdio_continue uffd_cont; + struct uffd_msg msg; + struct fault_args args; + pthread_t fault_thread; + void *mem, *mem_nofault, *buf = NULL; + int uffd, ret; + off_t offset = page_size; + void *fault_addr; + const char test_val = 0xcd; + + 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"); + + /* Map the guest_memfd twice: once with UFFD registered, once without */ + mem = mmap(NULL, total_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + TEST_ASSERT(mem != MAP_FAILED, "mmap should succeed"); + + mem_nofault = mmap(NULL, total_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + TEST_ASSERT(mem_nofault != MAP_FAILED, "mmap should succeed"); + + /* Register UFFD_MINOR on the first mapping */ + uffd_reg.range.start = (unsigned long)mem; + uffd_reg.range.len = total_size; + uffd_reg.mode = UFFDIO_REGISTER_MODE_MINOR; + ret = ioctl(uffd, UFFDIO_REGISTER, &uffd_reg); + TEST_ASSERT(ret != -1, "ioctl(UFFDIO_REGISTER) should succeed"); + + /* + * Populate the page in the page cache first via mem_nofault. + * This is required for UFFD_MINOR - the page must exist in the cache. + * Write test data to the page. + */ + memcpy(mem_nofault + offset, buf + offset, page_size); + + /* + * Now access the same page via mem (which has UFFD_MINOR registered). + * Since the page exists in the cache, this should trigger UFFD_MINOR. + */ + 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_MINOR, + "pagefault should be minor fault"); + + /* Resolve the minor fault with UFFDIO_CONTINUE */ + uffd_cont.range.start = (unsigned long)fault_addr; + uffd_cont.range.len = page_size; + uffd_cont.mode = 0; + ret = ioctl(uffd, UFFDIO_CONTINUE, &uffd_cont); + TEST_ASSERT(ret != -1, "ioctl(UFFDIO_CONTINUE) should succeed"); + + /* Wait for the faulting thread to complete */ + ret = pthread_join(fault_thread, NULL); + TEST_ASSERT(ret == 0, "pthread_join should succeed"); + + /* Verify the thread read the correct value */ + TEST_ASSERT(args.value == test_val, + "memory should contain the value that was written"); + TEST_ASSERT(*(char *)(mem + offset) == test_val, + "no further fault is expected"); + + ret = munmap(mem_nofault, total_size); + TEST_ASSERT(!ret, "munmap should succeed"); + + 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); @@ -383,6 +493,9 @@ static void __test_guest_memfd(struct kvm_vm *vm, uint64_t flags) gmem_test(file_size, vm, flags); gmem_test(fallocate, vm, flags); gmem_test(invalid_punch_hole, vm, flags); + + if (flags & GUEST_MEMFD_FLAG_INIT_SHARED) + gmem_test(uffd_minor, vm, flags); } static void test_guest_memfd(unsigned long vm_type) -- 2.53.0