Demonstrate a (very basic) scheme for supporting memory fault exits. >From the vCPU threads: 1. Simply issue UFFDIO_COPY/CONTINUEs in response to memory fault exits, with the purpose of establishing the absent mappings. Do so with wake_waiters=false to avoid serializing on the userfaultfd wait queue locks. 2. When the UFFDIO_COPY/CONTINUE in (1) fails with EEXIST, assume that the mapping was already established but is currently absent [A] and attempt to populate it using MADV_POPULATE_WRITE. Issue UFFDIO_COPY/CONTINUEs from the reader threads as well, but with wake_waiters=true to ensure that any threads sleeping on the uffd are eventually woken up. A real VMM would track whether it had already COPY/CONTINUEd pages (eg, via a bitmap) to avoid calls destined to EEXIST. However, even the naive approach is enough to demonstrate the performance advantages of KVM_EXIT_MEMORY_FAULT. [A] In reality it is much likelier that the vCPU thread simply lost a race to establish the mapping for the page. Signed-off-by: Anish Moorthy <amoorthy@xxxxxxxxxx> Acked-by: James Houghton <jthoughton@xxxxxxxxxx> --- .../selftests/kvm/demand_paging_test.c | 209 +++++++++++++----- 1 file changed, 155 insertions(+), 54 deletions(-) diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c index e84dde345edbc..668bd63d944e7 100644 --- a/tools/testing/selftests/kvm/demand_paging_test.c +++ b/tools/testing/selftests/kvm/demand_paging_test.c @@ -15,6 +15,7 @@ #include <time.h> #include <pthread.h> #include <linux/userfaultfd.h> +#include <sys/mman.h> #include <sys/syscall.h> #include "kvm_util.h" @@ -31,6 +32,57 @@ static uint64_t guest_percpu_mem_size = DEFAULT_PER_VCPU_MEM_SIZE; static size_t demand_paging_size; static char *guest_data_prototype; +static int num_uffds; +static size_t uffd_region_size; +static struct uffd_desc **uffd_descs; +/* + * Delay when demand paging is performed through userfaultfd or directly by + * vcpu_worker in the case of a KVM_EXIT_MEMORY_FAULT. + */ +static useconds_t uffd_delay; +static int uffd_mode; + + +static int handle_uffd_page_request(int uffd_mode, int uffd, uint64_t hva, + bool is_vcpu); + +static void madv_write_or_err(uint64_t gpa) +{ + int r; + void *hva = addr_gpa2hva(memstress_args.vm, gpa); + + r = madvise(hva, demand_paging_size, MADV_POPULATE_WRITE); + TEST_ASSERT(r == 0, + "MADV_POPULATE_WRITE on hva 0x%lx (gpa 0x%lx) fail, errno %i\n", + (uintptr_t) hva, gpa, errno); +} + +static void ready_page(uint64_t gpa) +{ + int r, uffd; + + /* + * This test only registers memslot 1 w/ userfaultfd. Any accesses outside + * the registered ranges should fault in the physical pages through + * MADV_POPULATE_WRITE. + */ + if ((gpa < memstress_args.gpa) + || (gpa >= memstress_args.gpa + memstress_args.size)) { + madv_write_or_err(gpa); + } else { + if (uffd_delay) + usleep(uffd_delay); + + uffd = uffd_descs[(gpa - memstress_args.gpa) / uffd_region_size]->uffd; + + r = handle_uffd_page_request(uffd_mode, uffd, + (uint64_t) addr_gpa2hva(memstress_args.vm, gpa), true); + + if (r == EEXIST) + madv_write_or_err(gpa); + } +} + static void vcpu_worker(struct memstress_vcpu_args *vcpu_args) { struct kvm_vcpu *vcpu = vcpu_args->vcpu; @@ -42,25 +94,36 @@ static void vcpu_worker(struct memstress_vcpu_args *vcpu_args) clock_gettime(CLOCK_MONOTONIC, &start); - /* Let the guest access its memory */ - ret = _vcpu_run(vcpu); - TEST_ASSERT(ret == 0, "vcpu_run failed: %d\n", ret); - if (get_ucall(vcpu, NULL) != UCALL_SYNC) { - TEST_ASSERT(false, - "Invalid guest sync status: exit_reason=%s\n", - exit_reason_str(run->exit_reason)); - } + while (true) { + /* Let the guest access its memory */ + ret = _vcpu_run(vcpu); + TEST_ASSERT(ret == 0 + || (errno == EFAULT + && run->exit_reason == KVM_EXIT_MEMORY_FAULT), + "vcpu_run failed: %d\n", ret); + if (ret != 0 && get_ucall(vcpu, NULL) != UCALL_SYNC) { + + if (run->exit_reason == KVM_EXIT_MEMORY_FAULT) { + ready_page(run->memory_fault.gpa); + continue; + } + + TEST_ASSERT(false, + "Invalid guest sync status: exit_reason=%s\n", + exit_reason_str(run->exit_reason)); + } - ts_diff = timespec_elapsed(start); - PER_VCPU_DEBUG("vCPU %d execution time: %ld.%.9lds\n", vcpu_idx, - ts_diff.tv_sec, ts_diff.tv_nsec); + ts_diff = timespec_elapsed(start); + PER_VCPU_DEBUG("vCPU %d execution time: %ld.%.9lds\n", vcpu_idx, + ts_diff.tv_sec, ts_diff.tv_nsec); + break; + } } -static int handle_uffd_page_request(int uffd_mode, int uffd, - struct uffd_msg *msg) +static int handle_uffd_page_request(int uffd_mode, int uffd, uint64_t hva, + bool is_vcpu) { pid_t tid = syscall(__NR_gettid); - uint64_t addr = msg->arg.pagefault.address; struct timespec start; struct timespec ts_diff; int r; @@ -71,56 +134,78 @@ static int handle_uffd_page_request(int uffd_mode, int uffd, struct uffdio_copy copy; copy.src = (uint64_t)guest_data_prototype; - copy.dst = addr; + copy.dst = hva; copy.len = demand_paging_size; - copy.mode = 0; + copy.mode = UFFDIO_COPY_MODE_DONTWAKE; - r = ioctl(uffd, UFFDIO_COPY, ©); /* - * With multiple vCPU threads fault on a single page and there are - * multiple readers for the UFFD, at least one of the UFFDIO_COPYs - * will fail with EEXIST: handle that case without signaling an - * error. + * With multiple vCPU threads and at least one of multiple reader threads + * or vCPU memory faults, multiple vCPUs accessing an absent page will + * almost certainly cause some thread doing the UFFDIO_COPY here to get + * EEXIST: make sure to allow that case. */ - if (r == -1 && errno != EEXIST) { - pr_info("Failed UFFDIO_COPY in 0x%lx from thread %d, errno = %d\n", - addr, tid, errno); - return r; - } + r = ioctl(uffd, UFFDIO_COPY, ©); + TEST_ASSERT(r == 0 || errno == EEXIST, + "Thread 0x%x failed UFFDIO_COPY on hva 0x%lx, errno = %d", + gettid(), hva, errno); } else if (uffd_mode == UFFDIO_REGISTER_MODE_MINOR) { + /* The comments in the UFFDIO_COPY branch also apply here. */ struct uffdio_continue cont = {0}; - cont.range.start = addr; + cont.range.start = hva; cont.range.len = demand_paging_size; + cont.mode = UFFDIO_CONTINUE_MODE_DONTWAKE; r = ioctl(uffd, UFFDIO_CONTINUE, &cont); - /* See the note about EEXISTs in the UFFDIO_COPY branch. */ - if (r == -1 && errno != EEXIST) { - pr_info("Failed UFFDIO_CONTINUE in 0x%lx, thread %d, errno = %d\n", - addr, tid, errno); - return r; - } + TEST_ASSERT(r == 0 || errno == EEXIST, + "Thread 0x%x failed UFFDIO_CONTINUE on hva 0x%lx, errno = %d", + gettid(), hva, errno); } else { TEST_FAIL("Invalid uffd mode %d", uffd_mode); } + /* + * If the above UFFDIO_COPY/CONTINUE fails with EEXIST, it will do so without + * waking threads waiting on the UFFD: make sure that happens here. + */ + if (!is_vcpu) { + struct uffdio_range range = { + .start = hva, + .len = demand_paging_size + }; + r = ioctl(uffd, UFFDIO_WAKE, &range); + TEST_ASSERT( + r == 0, + "Thread 0x%x failed UFFDIO_WAKE on hva 0x%lx, errno = %d", + gettid(), hva, errno); + } + ts_diff = timespec_elapsed(start); PER_PAGE_DEBUG("UFFD page-in %d \t%ld ns\n", tid, timespec_to_ns(ts_diff)); PER_PAGE_DEBUG("Paged in %ld bytes at 0x%lx from thread %d\n", - demand_paging_size, addr, tid); + demand_paging_size, hva, tid); return 0; } +static int handle_uffd_page_request_from_uffd(int uffd_mode, int uffd, + struct uffd_msg *msg) +{ + TEST_ASSERT(msg->event == UFFD_EVENT_PAGEFAULT, + "Received uffd message with event %d != UFFD_EVENT_PAGEFAULT", + msg->event); + return handle_uffd_page_request(uffd_mode, uffd, + msg->arg.pagefault.address, false); +} + struct test_params { - int uffd_mode; bool single_uffd; - useconds_t uffd_delay; int readers_per_uffd; enum vm_mem_backing_src_type src_type; bool partition_vcpu_memory_access; + bool memfault_exits; }; static void prefault_mem(void *alias, uint64_t len) @@ -137,15 +222,26 @@ static void prefault_mem(void *alias, uint64_t len) static void run_test(enum vm_guest_mode mode, void *arg) { struct test_params *p = arg; - struct uffd_desc **uffd_descs = NULL; struct timespec start; struct timespec ts_diff; struct kvm_vm *vm; - int i, num_uffds = 0; - uint64_t uffd_region_size; + int i; + uint32_t slot_flags = 0; + bool uffd_memfault_exits = uffd_mode && p->memfault_exits; + + if (uffd_memfault_exits) { + TEST_ASSERT(kvm_has_cap(KVM_CAP_ABSENT_MAPPING_FAULT) > 0, + "KVM does not have KVM_CAP_ABSENT_MAPPING_FAULT"); + slot_flags = KVM_MEM_ABSENT_MAPPING_FAULT; + } vm = memstress_create_vm(mode, nr_vcpus, guest_percpu_mem_size, - 1, 0, p->src_type, p->partition_vcpu_memory_access); + 1, slot_flags, p->src_type, p->partition_vcpu_memory_access); + + if (uffd_memfault_exits) { + vm_enable_cap(vm, + KVM_CAP_MEMORY_FAULT_INFO, KVM_MEMORY_FAULT_INFO_ENABLE); + } demand_paging_size = get_backing_src_pagesz(p->src_type); @@ -154,12 +250,12 @@ static void run_test(enum vm_guest_mode mode, void *arg) "Failed to allocate buffer for guest data pattern"); memset(guest_data_prototype, 0xAB, demand_paging_size); - if (p->uffd_mode) { + if (uffd_mode) { num_uffds = p->single_uffd ? 1 : nr_vcpus; uffd_region_size = nr_vcpus * guest_percpu_mem_size / num_uffds; uffd_descs = malloc(num_uffds * sizeof(struct uffd_desc *)); - TEST_ASSERT(uffd_descs, "Memory allocation failed"); + TEST_ASSERT(uffd_descs, "Failed to allocate memory of uffd descriptors"); for (i = 0; i < num_uffds; i++) { struct memstress_vcpu_args *vcpu_args; @@ -179,10 +275,10 @@ static void run_test(enum vm_guest_mode mode, void *arg) * requests. */ uffd_descs[i] = uffd_setup_demand_paging( - p->uffd_mode, p->uffd_delay, vcpu_hva, + uffd_mode, uffd_delay, vcpu_hva, uffd_region_size, p->readers_per_uffd, - &handle_uffd_page_request); + &handle_uffd_page_request_from_uffd); } } @@ -196,7 +292,7 @@ static void run_test(enum vm_guest_mode mode, void *arg) ts_diff = timespec_elapsed(start); pr_info("All vCPU threads joined\n"); - if (p->uffd_mode) { + if (uffd_mode) { /* Tell the user fault fd handler threads to quit */ for (i = 0; i < num_uffds; i++) uffd_stop_demand_paging(uffd_descs[i]); @@ -211,7 +307,7 @@ static void run_test(enum vm_guest_mode mode, void *arg) memstress_destroy_vm(vm); free(guest_data_prototype); - if (p->uffd_mode) + if (uffd_mode) free(uffd_descs); } @@ -220,7 +316,7 @@ static void help(char *name) puts(""); printf("usage: %s [-h] [-m vm_mode] [-u uffd_mode] [-a]\n" " [-d uffd_delay_usec] [-r readers_per_uffd] [-b memory]\n" - " [-s type] [-v vcpus] [-o]\n", name); + " [-w] [-s type] [-v vcpus] [-o]\n", name); guest_modes_help(); printf(" -u: use userfaultfd to handle vCPU page faults. Mode is a\n" " UFFD registration mode: 'MISSING' or 'MINOR'.\n"); @@ -231,6 +327,7 @@ static void help(char *name) " FD handler to simulate demand paging\n" " overheads. Ignored without -u.\n"); printf(" -r: Set the number of reader threads per uffd.\n"); + printf(" -w: Enable kvm cap for memory fault exits.\n"); printf(" -b: specify the size of the memory region which should be\n" " demand paged by each vCPU. e.g. 10M or 3G.\n" " Default: 1G\n"); @@ -250,29 +347,30 @@ int main(int argc, char *argv[]) .partition_vcpu_memory_access = true, .readers_per_uffd = 1, .single_uffd = false, + .memfault_exits = false, }; int opt; guest_modes_append_default(); - while ((opt = getopt(argc, argv, "ahom:u:d:b:s:v:r:")) != -1) { + while ((opt = getopt(argc, argv, "ahowm:u:d:b:s:v:r:")) != -1) { switch (opt) { case 'm': guest_modes_cmdline(optarg); break; case 'u': if (!strcmp("MISSING", optarg)) - p.uffd_mode = UFFDIO_REGISTER_MODE_MISSING; + uffd_mode = UFFDIO_REGISTER_MODE_MISSING; else if (!strcmp("MINOR", optarg)) - p.uffd_mode = UFFDIO_REGISTER_MODE_MINOR; - TEST_ASSERT(p.uffd_mode, "UFFD mode must be 'MISSING' or 'MINOR'."); + uffd_mode = UFFDIO_REGISTER_MODE_MINOR; + TEST_ASSERT(uffd_mode, "UFFD mode must be 'MISSING' or 'MINOR'."); break; case 'a': p.single_uffd = true; break; case 'd': - p.uffd_delay = strtoul(optarg, NULL, 0); - TEST_ASSERT(p.uffd_delay >= 0, "A negative UFFD delay is not supported."); + uffd_delay = strtoul(optarg, NULL, 0); + TEST_ASSERT(uffd_delay >= 0, "A negative UFFD delay is not supported."); break; case 'b': guest_percpu_mem_size = parse_size(optarg); @@ -295,6 +393,9 @@ int main(int argc, char *argv[]) "Invalid number of readers per uffd %d: must be >=1", p.readers_per_uffd); break; + case 'w': + p.memfault_exits = true; + break; case 'h': default: help(argv[0]); @@ -302,7 +403,7 @@ int main(int argc, char *argv[]) } } - if (p.uffd_mode == UFFDIO_REGISTER_MODE_MINOR && + if (uffd_mode == UFFDIO_REGISTER_MODE_MINOR && !backing_src_is_shared(p.src_type)) { TEST_FAIL("userfaultfd MINOR mode requires shared memory; pick a different -s"); } -- 2.40.0.577.gac1e443424-goog