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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Alban Crequy , Alban Crequy , Peter Xu , Willy Tarreau , linux-kselftest@vger.kernel.org, shuah@kernel.org Subject: [PATCH v2 2/2] selftests/mm: add tests for process_vm_readv flags Date: Wed, 8 Apr 2026 16:54:36 +0200 Message-ID: <20260408145436.843538-3-alban.crequy@gmail.com> X-Mailer: git-send-email 2.45.0 In-Reply-To: <20260408145436.843538-1-alban.crequy@gmail.com> References: <20260408145436.843538-1-alban.crequy@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Alban Crequy Add selftests for the PROCESS_VM_PIDFD and PROCESS_VM_NOWAIT flags introduced in process_vm_readv/writev. Tests cover: - basic read with no flags - invalid flags (EINVAL) - invalid address (EFAULT) - flag validation precedence over address validation - PROCESS_VM_PIDFD: read via pidfd - PROCESS_VM_NOWAIT: read from resident memory - PROCESS_VM_PIDFD | PROCESS_VM_NOWAIT combined - userfaultfd blocking read (no flags) - PROCESS_VM_NOWAIT with userfaultfd (non-blocking, returns EFAULT) Signed-off-by: Alban Crequy --- New in v2. tools/testing/selftests/mm/Makefile | 1 + tools/testing/selftests/mm/process_vm_readv.c | 368 ++++++++++++++++++ 2 files changed, 369 insertions(+) create mode 100644 tools/testing/selftests/mm/process_vm_readv.c diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile index 7a5de4e9bf52..056d9d961f6b 100644 --- a/tools/testing/selftests/mm/Makefile +++ b/tools/testing/selftests/mm/Makefile @@ -105,6 +105,7 @@ TEST_GEN_FILES += droppable TEST_GEN_FILES += guard-regions TEST_GEN_FILES += merge TEST_GEN_FILES += rmap +TEST_GEN_FILES += process_vm_readv ifneq ($(ARCH),arm64) TEST_GEN_FILES += soft-dirty diff --git a/tools/testing/selftests/mm/process_vm_readv.c b/tools/testing/selftests/mm/process_vm_readv.c new file mode 100644 index 000000000000..cc25471410b5 --- /dev/null +++ b/tools/testing/selftests/mm/process_vm_readv.c @@ -0,0 +1,368 @@ +// SPDX-License-Identifier: GPL-2.0-only +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "kselftest_harness.h" + +#ifndef PROCESS_VM_PIDFD +#define PROCESS_VM_PIDFD (1UL << 0) +#endif + +#ifndef PROCESS_VM_NOWAIT +#define PROCESS_VM_NOWAIT (1UL << 1) +#endif + +#ifndef __NR_pidfd_open +#define __NR_pidfd_open 434 +#endif + +static int sys_pidfd_open(pid_t pid, unsigned int flags) +{ + return syscall(__NR_pidfd_open, pid, flags); +} + +static const uint8_t test_data[] = { 0x01, 0x02, 0x03, 0x04, + 0x05, 0x06, 0x07, 0x08 }; +#define POISON_BYTE 0xCC + +/* + * Test: basic process_vm_readv with no flags + */ +TEST(read_basic) +{ + uint8_t buf[sizeof(test_data)]; + struct iovec local_iov = { .iov_base = buf, .iov_len = sizeof(buf) }; + struct iovec remote_iov = { + .iov_base = (void *)test_data, + .iov_len = sizeof(test_data) + }; + ssize_t n; + + memset(buf, POISON_BYTE, sizeof(buf)); + n = process_vm_readv(getpid(), &local_iov, 1, &remote_iov, 1, 0); + ASSERT_EQ(sizeof(test_data), n); + ASSERT_EQ(0, memcmp(buf, test_data, sizeof(test_data))); +} + +/* + * Test: invalid flags should return EINVAL + */ +TEST(read_invalid_flags) +{ + uint8_t buf[8] = { 0 }; + struct iovec local_iov = { .iov_base = buf, .iov_len = sizeof(buf) }; + struct iovec remote_iov = { + .iov_base = (void *)test_data, + .iov_len = sizeof(test_data) + }; + ssize_t n; + + n = process_vm_readv(getpid(), &local_iov, 1, &remote_iov, 1, 255); + ASSERT_EQ(-1, n); + ASSERT_EQ(EINVAL, errno); +} + +/* + * Test: invalid address should return EFAULT + */ +TEST(read_invalid_address) +{ + uint8_t buf[8] = { 0 }; + struct iovec local_iov = { .iov_base = buf, .iov_len = sizeof(buf) }; + struct iovec remote_iov = { .iov_base = NULL, .iov_len = 8 }; + ssize_t n; + + n = process_vm_readv(getpid(), &local_iov, 1, &remote_iov, 1, 0); + ASSERT_EQ(-1, n); + ASSERT_EQ(EFAULT, errno); +} + +/* + * Test: invalid address with invalid flags should return EINVAL + * (flag check happens before address validation) + */ +TEST(read_invalid_address_invalid_flags) +{ + uint8_t buf[8] = { 0 }; + struct iovec local_iov = { .iov_base = buf, .iov_len = sizeof(buf) }; + struct iovec remote_iov = { .iov_base = NULL, .iov_len = 8 }; + ssize_t n; + + n = process_vm_readv(getpid(), &local_iov, 1, &remote_iov, 1, 255); + ASSERT_EQ(-1, n); + ASSERT_EQ(EINVAL, errno); +} + +/* + * Test: invalid address with all valid flags should return EFAULT + * (flags are valid so we get past the flag check to the address check) + */ +TEST(read_invalid_address_all_valid_flags) +{ + int pidfd; + struct iovec local_iov = { .iov_base = NULL, .iov_len = 8 }; + struct iovec remote_iov = { .iov_base = NULL, .iov_len = 8 }; + ssize_t n; + + pidfd = sys_pidfd_open(getpid(), 0); + ASSERT_GE(pidfd, 0); + + n = process_vm_readv(pidfd, &local_iov, 1, &remote_iov, 1, + PROCESS_VM_PIDFD | PROCESS_VM_NOWAIT); + ASSERT_EQ(-1, n); + ASSERT_EQ(EFAULT, errno); + + close(pidfd); +} + +/* + * Test: read with PIDFD flag + */ +TEST(read_pidfd) +{ + uint8_t buf[sizeof(test_data)]; + struct iovec local_iov = { .iov_base = buf, .iov_len = sizeof(buf) }; + struct iovec remote_iov = { + .iov_base = (void *)test_data, + .iov_len = sizeof(test_data) + }; + ssize_t n; + int pidfd; + + memset(buf, POISON_BYTE, sizeof(buf)); + pidfd = sys_pidfd_open(getpid(), 0); + ASSERT_GE(pidfd, 0); + + n = process_vm_readv(pidfd, &local_iov, 1, &remote_iov, 1, + PROCESS_VM_PIDFD); + ASSERT_EQ(sizeof(test_data), n); + ASSERT_EQ(0, memcmp(buf, test_data, sizeof(test_data))); + + close(pidfd); +} + +/* + * Test: read with NOWAIT from resident memory (should succeed) + */ +TEST(read_nowait_resident) +{ + uint8_t buf[sizeof(test_data)]; + struct iovec local_iov = { .iov_base = buf, .iov_len = sizeof(buf) }; + struct iovec remote_iov = { + .iov_base = (void *)test_data, + .iov_len = sizeof(test_data) + }; + ssize_t n; + + memset(buf, POISON_BYTE, sizeof(buf)); + n = process_vm_readv(getpid(), &local_iov, 1, &remote_iov, 1, + PROCESS_VM_NOWAIT); + ASSERT_EQ(sizeof(test_data), n); + ASSERT_EQ(0, memcmp(buf, test_data, sizeof(test_data))); +} + +/* + * Test: read with PIDFD + NOWAIT from resident memory + */ +TEST(read_pidfd_nowait_resident) +{ + uint8_t buf[sizeof(test_data)]; + struct iovec local_iov = { .iov_base = buf, .iov_len = sizeof(buf) }; + struct iovec remote_iov = { + .iov_base = (void *)test_data, + .iov_len = sizeof(test_data) + }; + ssize_t n; + int pidfd; + + memset(buf, POISON_BYTE, sizeof(buf)); + pidfd = sys_pidfd_open(getpid(), 0); + ASSERT_GE(pidfd, 0); + + n = process_vm_readv(pidfd, &local_iov, 1, &remote_iov, 1, + PROCESS_VM_PIDFD | PROCESS_VM_NOWAIT); + ASSERT_EQ(sizeof(test_data), n); + ASSERT_EQ(0, memcmp(buf, test_data, sizeof(test_data))); + + close(pidfd); +} + +/* + * Userfaultfd helpers for NOWAIT tests + */ +static int setup_userfaultfd(void) +{ + struct uffdio_api api = { .api = UFFD_API }; + int uffd; + + uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK); + if (uffd < 0) + return -1; + + if (ioctl(uffd, UFFDIO_API, &api)) { + close(uffd); + return -1; + } + + return uffd; +} + +static void *register_uffd_region(int uffd, size_t size) +{ + struct uffdio_register reg; + void *mem; + + mem = mmap(NULL, size, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + if (mem == MAP_FAILED) + return NULL; + + reg.range.start = (unsigned long)mem; + reg.range.len = size; + reg.mode = UFFDIO_REGISTER_MODE_MISSING; + if (ioctl(uffd, UFFDIO_REGISTER, ®)) { + munmap(mem, size); + return NULL; + } + + return mem; +} + +struct uffd_handler_args { + int uffd; + const void *content; + size_t content_len; +}; + +static void *uffd_handler_thread(void *arg) +{ + struct uffd_handler_args *ha = arg; + struct uffd_msg msg; + struct uffdio_copy copy; + struct pollfd pfd = { + .fd = ha->uffd, + .events = POLLIN + }; + void *page; + long page_size = sysconf(_SC_PAGESIZE); + int ret; + + page = mmap(NULL, page_size, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + if (page == MAP_FAILED) + return (void *)(long)-ENOMEM; + + memcpy(page, ha->content, ha->content_len); + + ret = poll(&pfd, 1, 5000); + if (ret <= 0) + goto out; + + if (read(ha->uffd, &msg, sizeof(msg)) != sizeof(msg)) + goto out; + + if (msg.event != UFFD_EVENT_PAGEFAULT) + goto out; + + copy.dst = msg.arg.pagefault.address & ~(page_size - 1); + copy.src = (unsigned long)page; + copy.len = page_size; + copy.mode = 0; + ioctl(ha->uffd, UFFDIO_COPY, ©); + +out: + munmap(page, page_size); + return NULL; +} + +/* + * Test: read from userfaultfd-registered memory (no flags, should block + * until page fault is resolved by handler thread) + */ +TEST(read_userfaultfd_blocking) +{ + int uffd; + void *mem; + long page_size = sysconf(_SC_PAGESIZE); + uint8_t buf[sizeof(test_data)]; + struct iovec local_iov = { .iov_base = buf, .iov_len = sizeof(buf) }; + struct iovec remote_iov; + struct uffd_handler_args ha; + pthread_t handler; + ssize_t n; + + memset(buf, POISON_BYTE, sizeof(buf)); + + uffd = setup_userfaultfd(); + ASSERT_GE(uffd, 0); + + mem = register_uffd_region(uffd, page_size); + ASSERT_NE(NULL, mem); + + ha.uffd = uffd; + ha.content = test_data; + ha.content_len = sizeof(test_data); + ASSERT_EQ(0, pthread_create(&handler, NULL, uffd_handler_thread, &ha)); + + remote_iov.iov_base = mem; + remote_iov.iov_len = sizeof(test_data); + n = process_vm_readv(getpid(), &local_iov, 1, &remote_iov, 1, 0); + ASSERT_EQ(sizeof(test_data), n); + ASSERT_EQ(0, memcmp(buf, test_data, sizeof(test_data))); + + pthread_join(handler, NULL); + munmap(mem, page_size); + close(uffd); +} + +/* + * Test: read with NOWAIT from userfaultfd-registered memory that has + * not been faulted in yet. Should return EFAULT (not block). + */ +TEST(read_nowait_userfaultfd) +{ + int uffd; + void *mem; + long page_size = sysconf(_SC_PAGESIZE); + uint8_t buf[sizeof(test_data)] = { 0 }; + struct iovec local_iov = { .iov_base = buf, .iov_len = sizeof(buf) }; + struct iovec remote_iov; + ssize_t n; + + uffd = setup_userfaultfd(); + ASSERT_GE(uffd, 0); + + mem = register_uffd_region(uffd, page_size); + ASSERT_NE(NULL, mem); + + /* Ensure the page is not present */ + madvise(mem, page_size, MADV_DONTNEED); + + remote_iov.iov_base = mem; + remote_iov.iov_len = sizeof(test_data); + n = process_vm_readv(getpid(), &local_iov, 1, &remote_iov, 1, + PROCESS_VM_NOWAIT); + ASSERT_EQ(-1, n); + ASSERT_EQ(EFAULT, errno); + + munmap(mem, page_size); + close(uffd); +} + +TEST_HARNESS_MAIN -- 2.45.0