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Message-ID: <CANgfPd8oS7WJq9gbhK7rV3562KQM8xGXG981m=gq84dfcitYUA@mail.gmail.com>
Date: Wed, 19 May 2021 15:46:06 -0700
From: Ben Gardon <bgardon@...gle.com>
To: James Houghton <jthoughton@...gle.com>
Cc: Mike Kravetz <mike.kravetz@...cle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Shuah Khan <shuah@...nel.org>, linux-mm@...ck.org,
LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
linux-kselftest@...r.kernel.org,
Axel Rasmussen <axelrasmussen@...gle.com>,
Jue Wang <juew@...gle.com>, Peter Xu <peterx@...hat.com>,
Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 2/2] KVM: selftests: Add UFFD_FEATURE_SIGBUS page-in tests
On Wed, May 19, 2021 at 2:04 PM James Houghton <jthoughton@...gle.com> wrote:
>
> This exercises the KVM userfaultfd SIGBUS path to perform page-ins.
> This patch is based on Axel Rasmussen's patches that enable testing with
> HugeTLBFS:
> (https://lore.kernel.org/patchwork/patch/1432055/).
>
> This allows me to easily verify that the KVM patch does indeed work for
> anonymous, shmem-backed, and hugetlbfs-backed pages.
>
> Signed-off-by: James Houghton <jthoughton@...gle.com>
> ---
> .../selftests/kvm/demand_paging_test.c | 193 +++++++++++++-----
If you'd be willing to split this patch up into a few smaller patches,
I'd find it much easier to review.
Thank you for updating this test with your SIGBUS patch.
> 1 file changed, 138 insertions(+), 55 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c
> index 60d9b5223b9d..fe5f6fdf4b28 100644
> --- a/tools/testing/selftests/kvm/demand_paging_test.c
> +++ b/tools/testing/selftests/kvm/demand_paging_test.c
> @@ -10,6 +10,7 @@
> #define _GNU_SOURCE /* for pipe2 */
>
> #include <inttypes.h>
> +#include <stdatomic.h>
> #include <stdint.h>
> #include <stdio.h>
> #include <stdlib.h>
> @@ -17,6 +18,7 @@
> #include <poll.h>
> #include <pthread.h>
> #include <linux/userfaultfd.h>
> +#include <signal.h>
> #include <sys/syscall.h>
>
> #include "kvm_util.h"
> @@ -43,37 +45,25 @@ static uint64_t guest_percpu_mem_size = DEFAULT_PER_VCPU_MEM_SIZE;
> static size_t demand_paging_size;
> static char *guest_data_prototype;
>
> -static void *vcpu_worker(void *data)
> -{
> - int ret;
> - struct perf_test_vcpu_args *vcpu_args = (struct perf_test_vcpu_args *)data;
> - int vcpu_id = vcpu_args->vcpu_id;
> - struct kvm_vm *vm = perf_test_args.vm;
> - struct kvm_run *run;
> - struct timespec start;
> - struct timespec ts_diff;
> -
> - vcpu_args_set(vm, vcpu_id, 1, vcpu_id);
> - run = vcpu_state(vm, vcpu_id);
> -
> - clock_gettime(CLOCK_MONOTONIC, &start);
> -
> - /* Let the guest access its memory */
> - ret = _vcpu_run(vm, vcpu_id);
> - TEST_ASSERT(ret == 0, "vcpu_run failed: %d\n", ret);
> - if (get_ucall(vm, vcpu_id, NULL) != UCALL_SYNC) {
> - TEST_ASSERT(false,
> - "Invalid guest sync status: exit_reason=%s\n",
> - exit_reason_str(run->exit_reason));
> - }
> +__thread uint64_t sigbus_address;
> +__thread atomic_bool sigbus_pending_fault;
>
> - ts_diff = timespec_elapsed(start);
> - PER_VCPU_DEBUG("vCPU %d execution time: %ld.%.9lds\n", vcpu_id,
> - ts_diff.tv_sec, ts_diff.tv_nsec);
> +static void handle_uffd_sigbus(int signum, siginfo_t *info, void *ctx)
> +{
> + // Round down address.
> + uint64_t mask = ~(demand_paging_size - 1);
>
> - return NULL;
> + sigbus_address = (unsigned long long)(info->si_addr) & mask;
> + atomic_store_explicit(&sigbus_pending_fault, true, memory_order_release);
> }
>
> +struct vcpu_worker_args {
> + struct perf_test_vcpu_args *vcpu_args;
> + int uffd;
> + int uffd_mode;
> + bool use_uffd_sigbus;
> +};
> +
> static int handle_uffd_page_request(int uffd_mode, int uffd, uint64_t addr)
> {
> pid_t tid = syscall(__NR_gettid);
> @@ -123,6 +113,53 @@ static int handle_uffd_page_request(int uffd_mode, int uffd, uint64_t addr)
> return 0;
> }
>
> +static void *vcpu_worker(void *data)
> +{
> + int ret;
> + struct vcpu_worker_args *vcpu_worker_args =
> + (struct vcpu_worker_args *)data;
> + struct perf_test_vcpu_args *vcpu_args = vcpu_worker_args->vcpu_args;
> + int vcpu_id = vcpu_args->vcpu_id;
> + struct kvm_vm *vm = perf_test_args.vm;
> + struct kvm_run *run;
> + struct timespec start;
> + struct timespec ts_diff;
> +
> + vcpu_args_set(vm, vcpu_id, 1, vcpu_id);
> + run = vcpu_state(vm, vcpu_id);
> +
> + clock_gettime(CLOCK_MONOTONIC, &start);
> +
> + /* Let the guest access its memory */
> + for (;;) {
> + ret = _vcpu_run(vm, vcpu_id);
> + if (vcpu_worker_args->use_uffd_sigbus &&
> + atomic_load_explicit(&sigbus_pending_fault,
> + memory_order_acquire)) {
> + int r = handle_uffd_page_request(
> + vcpu_worker_args->uffd_mode,
> + vcpu_worker_args->uffd, sigbus_address);
> + TEST_ASSERT(r == 0, "handle_uffd_page_request failed");
> + atomic_store_explicit(&sigbus_pending_fault, false,
> + memory_order_relaxed);
> + } else
> + break;
> + }
> +
> + TEST_ASSERT(ret == 0, "vcpu_run failed: %d\n", ret);
> + if (get_ucall(vm, vcpu_id, NULL) != UCALL_SYNC) {
> + 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_id,
> + ts_diff.tv_sec, ts_diff.tv_nsec);
> +
> + return NULL;
> +}
> +
> bool quit_uffd_thread;
>
> struct uffd_handler_args {
> @@ -217,11 +254,8 @@ static void *uffd_handler_thread_fn(void *arg)
> return NULL;
> }
>
> -static void setup_demand_paging(struct kvm_vm *vm,
> - pthread_t *uffd_handler_thread, int pipefd,
> - int uffd_mode, useconds_t uffd_delay,
> - struct uffd_handler_args *uffd_args,
> - void *hva, void *alias, uint64_t len)
> +static int create_userfaultfd(int uffd_mode, bool use_uffd_sigbus,
> + void *hva, void *alias, uint64_t len)
> {
> bool is_minor = (uffd_mode == UFFDIO_REGISTER_MODE_MINOR);
> int uffd;
> @@ -250,7 +284,7 @@ static void setup_demand_paging(struct kvm_vm *vm,
> TEST_ASSERT(uffd >= 0, "uffd creation failed, errno: %d", errno);
>
> uffdio_api.api = UFFD_API;
> - uffdio_api.features = 0;
> + uffdio_api.features = use_uffd_sigbus ? UFFD_FEATURE_SIGBUS : 0;
> TEST_ASSERT(ioctl(uffd, UFFDIO_API, &uffdio_api) != -1,
> "ioctl UFFDIO_API failed: %" PRIu64,
> (uint64_t)uffdio_api.api);
> @@ -263,19 +297,29 @@ static void setup_demand_paging(struct kvm_vm *vm,
> TEST_ASSERT((uffdio_register.ioctls & expected_ioctls) ==
> expected_ioctls, "missing userfaultfd ioctls");
>
> + return uffd;
> +}
> +
> +static void start_uffd_thread(pthread_t *uffd_handler_thread, int *pipefds,
> + int uffd, int uffd_mode, useconds_t uffd_delay,
> + struct uffd_handler_args *uffd_args)
> +{
> + int r;
> +
> + r = pipe2(pipefds, O_CLOEXEC | O_NONBLOCK);
> + TEST_ASSERT(!r, "Failed to set up pipefd");
> +
> uffd_args->uffd_mode = uffd_mode;
> uffd_args->uffd = uffd;
> - uffd_args->pipefd = pipefd;
> + uffd_args->pipefd = pipefds[0];
> uffd_args->delay = uffd_delay;
> pthread_create(uffd_handler_thread, NULL, uffd_handler_thread_fn,
> uffd_args);
> -
> - PER_VCPU_DEBUG("Created uffd thread for HVA range [%p, %p)\n",
> - hva, hva + len);
> }
>
> struct test_params {
> int uffd_mode;
> + bool use_uffd_sigbus;
> useconds_t uffd_delay;
> enum vm_mem_backing_src_type src_type;
> bool partition_vcpu_memory_access;
> @@ -286,6 +330,7 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> struct test_params *p = arg;
> pthread_t *vcpu_threads;
> pthread_t *uffd_handler_threads = NULL;
> + struct vcpu_worker_args *vcpu_worker_args = NULL;
> struct uffd_handler_args *uffd_args = NULL;
> struct timespec start;
> struct timespec ts_diff;
> @@ -293,6 +338,7 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> struct kvm_vm *vm;
> int vcpu_id;
> int r;
> + bool uffd_threads_needed;
>
> vm = perf_test_create_vm(mode, nr_vcpus, guest_percpu_mem_size,
> p->src_type);
> @@ -309,10 +355,16 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> vcpu_threads = malloc(nr_vcpus * sizeof(*vcpu_threads));
> TEST_ASSERT(vcpu_threads, "Memory allocation failed");
>
> + vcpu_worker_args = malloc(nr_vcpus * sizeof(*vcpu_worker_args));
> + TEST_ASSERT(vcpu_worker_args, "Memory allocation failed");
> +
> perf_test_setup_vcpus(vm, nr_vcpus, guest_percpu_mem_size,
> p->partition_vcpu_memory_access);
>
> - if (p->uffd_mode) {
> + uffd_threads_needed = p->uffd_mode && !p->use_uffd_sigbus;
> + if (uffd_threads_needed) {
> + // Handler threads are not necessary when using
> + // UFFD_FEATURE_SIGBUS.
> uffd_handler_threads =
> malloc(nr_vcpus * sizeof(*uffd_handler_threads));
> TEST_ASSERT(uffd_handler_threads, "Memory allocation failed");
> @@ -322,6 +374,21 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>
> pipefds = malloc(sizeof(int) * nr_vcpus * 2);
> TEST_ASSERT(pipefds, "Unable to allocate memory for pipefd");
> + }
> +
> + if (p->use_uffd_sigbus) {
> + struct sigaction action;
> +
> + memset(&action, 0, sizeof(action));
> + action.sa_sigaction = handle_uffd_sigbus;
> + action.sa_flags = SA_SIGINFO;
> + if (sigaction(SIGBUS, &action, NULL) < 0) {
> + perror("Failed to set sigaction");
> + return;
> + }
> + }
> +
> + if (p->uffd_mode) {
>
> for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++) {
> vm_paddr_t vcpu_gpa;
> @@ -329,7 +396,6 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> void *vcpu_alias;
> uint64_t vcpu_mem_size;
>
> -
> if (p->partition_vcpu_memory_access) {
> vcpu_gpa = guest_test_phys_mem +
> (vcpu_id * guest_percpu_mem_size);
> @@ -339,7 +405,8 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> vcpu_mem_size = guest_percpu_mem_size * nr_vcpus;
> }
> PER_VCPU_DEBUG("Added VCPU %d with test mem gpa [%lx, %lx)\n",
> - vcpu_id, vcpu_gpa, vcpu_gpa + vcpu_mem_size);
> + vcpu_id, vcpu_gpa,
> + vcpu_gpa + vcpu_mem_size);
>
> /* Cache the host addresses of the region */
> vcpu_hva = addr_gpa2hva(vm, vcpu_gpa);
> @@ -349,28 +416,39 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> * Set up user fault fd to handle demand paging
> * requests.
> */
> - r = pipe2(&pipefds[vcpu_id * 2],
> - O_CLOEXEC | O_NONBLOCK);
> - TEST_ASSERT(!r, "Failed to set up pipefd");
> -
> - setup_demand_paging(vm, &uffd_handler_threads[vcpu_id],
> - pipefds[vcpu_id * 2], p->uffd_mode,
> - p->uffd_delay, &uffd_args[vcpu_id],
> - vcpu_hva, vcpu_alias,
> - vcpu_mem_size);
> + r = create_userfaultfd(p->uffd_mode, p->use_uffd_sigbus,
> + vcpu_hva, vcpu_alias,
> + vcpu_mem_size);
> + if (r < 0)
> + exit(-r);
> +
> + if (uffd_threads_needed) {
> + start_uffd_thread(&uffd_handler_threads[vcpu_id],
> + &pipefds[vcpu_id * 2],
> + r, p->uffd_mode, p->uffd_delay,
> + &uffd_args[vcpu_id]);
> + PER_VCPU_DEBUG("Created uffd thread for HVA range [%p, %p)\n",
> + vcpu_hva, vcpu_hva + vcpu_mem_size);
> + }
> +
> + vcpu_worker_args[vcpu_id].uffd = r;
> }
> }
>
> /* Export the shared variables to the guest */
> sync_global_to_guest(vm, perf_test_args);
>
> - pr_info("Finished creating vCPUs and starting uffd threads\n");
> + pr_info("Finished creating vCPUs\n");
>
> clock_gettime(CLOCK_MONOTONIC, &start);
>
> for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++) {
> + vcpu_worker_args[vcpu_id].vcpu_args =
> + &perf_test_args.vcpu_args[vcpu_id];
> + vcpu_worker_args[vcpu_id].use_uffd_sigbus = p->use_uffd_sigbus;
> + vcpu_worker_args[vcpu_id].uffd_mode = p->uffd_mode;
> pthread_create(&vcpu_threads[vcpu_id], NULL, vcpu_worker,
> - &perf_test_args.vcpu_args[vcpu_id]);
> + &vcpu_worker_args[vcpu_id]);
> }
>
> pr_info("Started all vCPUs\n");
> @@ -385,7 +463,7 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>
> pr_info("All vCPU threads joined\n");
>
> - if (p->uffd_mode) {
> + if (uffd_threads_needed) {
> char c;
>
> /* Tell the user fault fd handler threads to quit */
> @@ -407,7 +485,8 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>
> free(guest_data_prototype);
> free(vcpu_threads);
> - if (p->uffd_mode) {
> + free(vcpu_worker_args);
> + if (uffd_threads_needed) {
> free(uffd_handler_threads);
> free(uffd_args);
> free(pipefds);
> @@ -417,11 +496,12 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> static void help(char *name)
> {
> puts("");
> - printf("usage: %s [-h] [-m mode] [-u mode] [-d uffd_delay_usec]\n"
> + printf("usage: %s [-h] [-m mode] [-u mode] [-s] [-d uffd_delay_usec]\n"
> " [-b memory] [-t 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");
> + printf(" -s: use UFFD_FEATURE_SIGBUS to perform page-ins.\n");
> printf(" -d: add a delay in usec to the User Fault\n"
> " FD handler to simulate demand paging\n"
> " overheads. Ignored without -u.\n");
> @@ -448,7 +528,7 @@ int main(int argc, char *argv[])
>
> guest_modes_append_default();
>
> - while ((opt = getopt(argc, argv, "hm:u:d:b:t:v:o")) != -1) {
> + while ((opt = getopt(argc, argv, "hm:u:sd:b:t:v:o")) != -1) {
> switch (opt) {
> case 'm':
> guest_modes_cmdline(optarg);
> @@ -460,6 +540,9 @@ int main(int argc, char *argv[])
> p.uffd_mode = UFFDIO_REGISTER_MODE_MINOR;
> TEST_ASSERT(p.uffd_mode, "UFFD mode must be 'MISSING' or 'MINOR'.");
> break;
> + case 's':
> + p.use_uffd_sigbus = true;
> + break;
> case 'd':
> p.uffd_delay = strtoul(optarg, NULL, 0);
> TEST_ASSERT(p.uffd_delay >= 0, "A negative UFFD delay is not supported.");
> --
> 2.31.1.751.gd2f1c929bd-goog
>
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