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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 16/17] KVM: selftests: test userfaultfd minor for guest_memfd Date: Tue, 27 Jan 2026 21:29:35 +0200 Message-ID: <20260127192936.1250096-17-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-Stat-Signature: njo59rshxgwtpq85d3ebz5uzc11xoz3o X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: F15CE40013 X-HE-Tag: 1769542288-618851 X-HE-Meta: U2FsdGVkX1+dgfVQ6zckmIDMhBEPWpLE/owvRCrH49wq5koMFjs2XkrElgfnS/Mh0GsazHVKQzymivrI4qAQ54JyrXOhNAFd3jAUpS0DoLMOS/kZ7Y+oepxpHWeiB8qvYwPsQgYAKeLRkoEZOF2oaQHq8fQZhPtvOKHkLj98Wp/ILMx+IAJBuVHOxwVNfPUlwYXrDH1OMY3Zb4pXd08+PZEfOf7FWls708/aez7VJuBvKcrOA+0D4q3WXkLWImwzsZXsmbEm0WWAZFwnUKTd/nbBTyEm7DUddv0sZJcj3G/1RpZEE5xnmrf459bN7qT5aoL9IG2aNcYWSeD8uGH3JccHc3ZkK18Oqb2JI9AdaYArBqYaMQH7oeEEg8hmkWeHvg4a+2g3NVMXTrAGcwbvaFYY9sWs1vrjAp9PwJ4lDA3d5suh/6muGejBzcJUHO2dRPYdpYCi1rThfJHS5UfP0Sk9CBduIfKnW0stOES1qePLvkP5GUyOXnZcaabNpPyJaXg7D5MBzx2Z1WCvoInf9uDXxpBtqeRIrteFp5+hu2P7yy3oUblQSbm/fvCpSPjXaDFvZD3RPORet7nxbw0NDFPdZBSdRUXZ0UV/83mwlB457BJ4f2VLNHc9fRsKRbTy1rAUQMmhfW8GL+Lr/R57Q8KBye2uTmsjXLAW2N4aGO7cDoTFWoZ6740cMvccAOSMUmygwY3ScHeX3NVyhIx0cyktUKWu4HJpfSkECfwnDXaq7Bw4DAgAby44w+tAJTznC6u6s+tHhR/ZDReh70rvWoDcHvFjR8LXud/phrnYbHQRiYlFl8tt+4FZKCkZbEJ9fQU628VN+ZsqvowHxawt8GRTcL/YZrKNyIIqfNTPpzTLwaT7gm5XPRD81G7gqB80Q7d9aJf0Po8EsaJSI62A3yUzR3QIJ8bFoJX896LUXUc4SlFTIRXbtQOBNtzZGx9GRczvYbO2dotLiLnwsKf IGvnL/JI PnOsRhx329sdY9jga70lK0ddA3/HwFzqiOfaDMJJ9jX65fMItLLDl3PAxNwxc5qzp/AQgb6G11LJTuKmQzNR9xGXd6XFWUDZiZBMMaELY5qb9l77kxA1CDhynPzGveWOTIwKxHYWlRq7v/w5CauVp9V2RPWLwjvuDNAXx74ijFGPiaEjX59JT/PlfFQ/MVjOl2yV1V4NQlYA6Ud1xNgR6G976iCMHwPWeZ0SKysw+crvUig3zNE7nkw4Q3AlJVt7e0ncUfuU77VuKnm5vso/FoKuJXcIWi1AxnGUK+oGsJW96j78IVLDH4LqT0Q== 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 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 618c937f3c90..7612819e340a 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) -- 2.51.0