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Thu, 3 Apr 2025 17:02:37 +0000 Message-ID: <3a54adea-98d0-4af3-a121-6574b0c18f80@amazon.com> Date: Thu, 3 Apr 2025 18:02:36 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: Subject: Re: [PATCH v2 5/5] KVM: selftests: test userfaultfd minor for guest_memfd To: James Houghton CC: , , , , , , , , , , , , , , , , , References: <20250402160721.97596-1-kalyazin@amazon.com> <20250402160721.97596-6-kalyazin@amazon.com> Content-Language: en-US From: Nikita Kalyazin Autocrypt: addr=kalyazin@amazon.com; keydata= xjMEY+ZIvRYJKwYBBAHaRw8BAQdA9FwYskD/5BFmiiTgktstviS9svHeszG2JfIkUqjxf+/N JU5pa2l0YSBLYWx5YXppbiA8a2FseWF6aW5AYW1hem9uLmNvbT7CjwQTFggANxYhBGhhGDEy BjLQwD9FsK+SyiCpmmTzBQJnrNfABQkFps9DAhsDBAsJCAcFFQgJCgsFFgIDAQAACgkQr5LK IKmaZPOpfgD/exazh4C2Z8fNEz54YLJ6tuFEgQrVQPX6nQ/PfQi2+dwBAMGTpZcj9Z9NvSe1 CmmKYnYjhzGxzjBs8itSUvWIcMsFzjgEY+ZIvRIKKwYBBAGXVQEFAQEHQCqd7/nb2tb36vZt ubg1iBLCSDctMlKHsQTp7wCnEc4RAwEIB8J+BBgWCAAmFiEEaGEYMTIGMtDAP0Wwr5LKIKma ZPMFAmes18AFCQWmz0MCGwwACgkQr5LKIKmaZPNTlQEA+q+rGFn7273rOAg+rxPty0M8lJbT i2kGo8RmPPLu650A/1kWgz1AnenQUYzTAFnZrKSsXAw5WoHaDLBz9kiO5pAK In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: EX19D009EUA003.ant.amazon.com (10.252.50.105) To EX19D022EUC002.ant.amazon.com (10.252.51.137) On 02/04/2025 22:10, James Houghton wrote: > On Wed, Apr 2, 2025 at 9:08 AM Nikita Kalyazin wrote: >> >> 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 >> --- >> .../testing/selftests/kvm/guest_memfd_test.c | 94 +++++++++++++++++++ >> 1 file changed, 94 insertions(+) >> >> diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c >> index 38c501e49e0e..9b47b796f3aa 100644 >> --- a/tools/testing/selftests/kvm/guest_memfd_test.c >> +++ b/tools/testing/selftests/kvm/guest_memfd_test.c >> @@ -10,12 +10,16 @@ >> #include >> #include >> #include >> +#include >> >> #include >> #include >> +#include >> #include >> #include >> #include >> +#include >> +#include >> >> #include "kvm_util.h" >> #include "test_util.h" >> @@ -206,6 +210,93 @@ static void test_create_guest_memfd_multiple(struct kvm_vm *vm) >> close(fd1); >> } >> >> +struct fault_args { >> + char *addr; >> + volatile char value; > > I think you should/must put volatile on `addr` and not on `value`. This was to prevent the compiler from omitting the write to the value, because it's never read later on. > >> +}; >> + >> +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_missing(int fd, size_t page_size, size_t total_size) > > test_uffd_minor? :) > >> +{ >> + 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; >> + >> + ret = posix_memalign(&buf, page_size, total_size); >> + TEST_ASSERT_EQ(ret, 0); >> + >> + uffd = syscall(__NR_userfaultfd, O_CLOEXEC); >> + TEST_ASSERT(uffd != -1, "userfaultfd creation should succeed"); >> + >> + struct uffdio_api uffdio_api = { >> + .api = UFFD_API, >> + .features = UFFD_FEATURE_MISSING_SHMEM, > > I think you mean UFFD_FEATURE_MINOR_SHMEM...? > > And I'm trying to think through what feature we should expose for > guest_memfd; UFFD_FEATURE_MINOR_SHMEM already indicates support for > shmem. > > We could have UFFD_FEATURE_MINOR_GUESTMEMFD, perhaps that's enough. Yes, I will introduce UFFD_FEATURE_MINOR_GUEST_MEMFD in the next version. > > Or we could have UFFD_FEATURE_MINOR_GENERIC (or nothing at all!). Some > VMAs might not support the minor mode, and the user will figure that > out when UFFDIO_REGISTER fails. My concern is the exact reason of the failure may not be apparent to the caller in that case. > >> + }; >> + 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"); >> + >> + mem_nofault = mmap(NULL, total_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); >> + TEST_ASSERT(mem_nofault != MAP_FAILED, "mmap should succeed"); >> + >> + 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"); >> + >> + ret = fallocate(fd, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE, >> + offset, page_size); >> + TEST_ASSERT(!ret, "fallocate(PUNCH_HOLE) 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"); >> + >> + memcpy(mem_nofault + offset, buf + offset, page_size); >> + >> + 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"); >> + >> + ret = pthread_join(fault_thread, NULL); >> + TEST_ASSERT(ret == 0, "pthread_join should succeed"); > > And maybe also: > > /* Right value? */ > TEST_ASSERT(args.value == *(char *)mem_nofault)); > /* No second fault? */ > TEST_ASSERT(args.value == *(char *)mem); Good idea, thanks. I don't need the volatile anymore :) > >> + >> + 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); >> +} >> + >> unsigned long get_shared_type(void) >> { >> #ifdef __x86_64__ >> @@ -244,6 +335,9 @@ void test_vm_type(unsigned long type, bool is_shared) >> test_fallocate(fd, page_size, total_size); >> test_invalid_punch_hole(fd, page_size, total_size); >> >> + if (is_shared) >> + test_uffd_missing(fd, page_size, total_size); >> + >> close(fd); >> kvm_vm_release(vm); >> } >> -- >> 2.47.1 >>