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Message-ID: <CANgfPd9LpH2z2b5J1n59GXMLM1vfDzfsdgydcAHOfw3j61+grw@mail.gmail.com>
Date: Tue, 18 May 2021 12:05:29 -0700
From: Ben Gardon <bgardon@...gle.com>
To: Axel Rasmussen <axelrasmussen@...gle.com>
Cc: Aaron Lewis <aaronlewis@...gle.com>,
Alexander Graf <graf@...zon.com>,
Andrew Jones <drjones@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Emanuele Giuseppe Esposito <eesposit@...hat.com>,
Eric Auger <eric.auger@...hat.com>,
Jacob Xu <jacobhxu@...gle.com>,
Makarand Sonare <makarandsonare@...gle.com>,
Oliver Upton <oupton@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Peter Xu <peterx@...hat.com>, Shuah Khan <shuah@...nel.org>,
Yanan Wang <wangyanan55@...wei.com>, kvm <kvm@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 4/5] KVM: selftests: allow using UFFD minor faults for
demand paging
On Tue, May 18, 2021 at 11:17 AM Axel Rasmussen
<axelrasmussen@...gle.com> wrote:
>
> On Mon, May 17, 2021 at 4:51 PM Ben Gardon <bgardon@...gle.com> wrote:
> >
> > On Wed, May 12, 2021 at 2:45 PM Axel Rasmussen <axelrasmussen@...gle.com> wrote:
> > >
> > > UFFD handling of MINOR faults is a new feature whose use case is to
> > > speed up demand paging (compared to MISSING faults). So, it's
> > > interesting to let this selftest exercise this new mode.
> > >
> > > Modify the demand paging test to have the option of using UFFD minor
> > > faults, as opposed to missing faults. Now, when turning on userfaultfd
> > > with '-u', the desired mode has to be specified ("MISSING" or "MINOR").
> > >
> > > If we're in minor mode, before registering, prefault via the *alias*.
> > > This way, the guest will trigger minor faults, instead of missing
> > > faults, and we can UFFDIO_CONTINUE to resolve them.
> > >
> > > Modify the page fault handler function to use the right ioctl depending
> > > on the mode we're running in. In MINOR mode, use UFFDIO_CONTINUE.
> > >
> > > Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>
> > > ---
> > > .../selftests/kvm/demand_paging_test.c | 124 ++++++++++++------
> > > 1 file changed, 87 insertions(+), 37 deletions(-)
> > >
> > > diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c
> > > index 10c7ba76a9c6..ff29aaea3120 100644
> > > --- a/tools/testing/selftests/kvm/demand_paging_test.c
> > > +++ b/tools/testing/selftests/kvm/demand_paging_test.c
> > > @@ -72,33 +72,57 @@ static void *vcpu_worker(void *data)
> > > return NULL;
> > > }
> > >
> > > -static int handle_uffd_page_request(int uffd, uint64_t addr)
> > > +static int handle_uffd_page_request(int uffd_mode, int uffd, uint64_t addr)
> > > {
> > > - pid_t tid;
> > > + const char *ioctl_name;
> > > + pid_t tid = syscall(__NR_gettid);
> > > struct timespec start;
> > > struct timespec ts_diff;
> > > - struct uffdio_copy copy;
> > > int r;
> > >
> > > - tid = syscall(__NR_gettid);
> > > + if (uffd_mode == UFFDIO_REGISTER_MODE_MISSING) {
> > > + struct uffdio_copy copy;
> > >
> > > - copy.src = (uint64_t)guest_data_prototype;
> > > - copy.dst = addr;
> > > - copy.len = demand_paging_size;
> > > - copy.mode = 0;
> > > + ioctl_name = "UFFDIO_COPY";
> > >
> > > - clock_gettime(CLOCK_MONOTONIC, &start);
> > > + copy.src = (uint64_t)guest_data_prototype;
> > > + copy.dst = addr;
> > > + copy.len = demand_paging_size;
> > > + copy.mode = 0;
> > >
> > > - r = ioctl(uffd, UFFDIO_COPY, ©);
> > > - if (r == -1) {
> > > - pr_info("Failed Paged in 0x%lx from thread %d with errno: %d\n",
> > > - addr, tid, errno);
> > > - return r;
> > > - }
> > > + clock_gettime(CLOCK_MONOTONIC, &start);
> >
> > Nit: It'd probably be fine to factor the timing calls out of the if
> > statement to deduplicate.
> >
> > >
> > > - ts_diff = timespec_elapsed(start);
> > > + r = ioctl(uffd, UFFDIO_COPY, ©);
> > > + if (r == -1) {
> > > + pr_info("Failed UFFDIO_COPY in 0x%lx from thread %d with errno: %d\n",
> > > + addr, tid, errno);
> > > + return r;
> > > + }
> > > +
> > > + ts_diff = timespec_elapsed(start);
> > > + } else if (uffd_mode == UFFDIO_REGISTER_MODE_MINOR) {
> > > + struct uffdio_continue cont = {0};
> > > +
> > > + ioctl_name = "UFFDIO_CONTINUE";
> > > +
> > > + cont.range.start = addr;
> > > + cont.range.len = demand_paging_size;
> > > +
> > > + clock_gettime(CLOCK_MONOTONIC, &start);
> > > +
> > > + r = ioctl(uffd, UFFDIO_CONTINUE, &cont);
> > > + if (r == -1) {
> > > + pr_info("Failed UFFDIO_CONTINUE in 0x%lx from thread %d with errno: %d\n",
> > > + addr, tid, errno);
> > > + return r;
> > > + }
> > >
> > > - PER_PAGE_DEBUG("UFFDIO_COPY %d \t%ld ns\n", tid,
> > > + ts_diff = timespec_elapsed(start);
> > > + } else {
> > > + TEST_FAIL("Invalid uffd mode %d", uffd_mode);
> > > + }
> > > +
> > > + PER_PAGE_DEBUG("%s %d \t%ld ns\n", ioctl_name, tid,
> > > timespec_to_ns(ts_diff));
> >
> > As far as I can see this is the only use of ioctl_name and it's not
> > going to change in a test run, so it might make sense to not print the
> > ioctl name here and just do it once somewhere else.
> >
> > > PER_PAGE_DEBUG("Paged in %ld bytes at 0x%lx from thread %d\n",
> > > demand_paging_size, addr, tid);
> > > @@ -109,6 +133,7 @@ static int handle_uffd_page_request(int uffd, uint64_t addr)
> > > bool quit_uffd_thread;
> > >
> > > struct uffd_handler_args {
> > > + int uffd_mode;
> > > int uffd;
> > > int pipefd;
> > > useconds_t delay;
> > > @@ -170,7 +195,7 @@ static void *uffd_handler_thread_fn(void *arg)
> > > if (r == -1) {
> > > if (errno == EAGAIN)
> > > continue;
> > > - pr_info("Read of uffd gor errno %d", errno);
> > > + pr_info("Read of uffd got errno %d\n", errno);
> >
> > If you end up doing some kind of cleanups patch, it might be worth
> > moving this in there.
> >
> > > return NULL;
> > > }
> > >
> > > @@ -185,7 +210,7 @@ static void *uffd_handler_thread_fn(void *arg)
> > > if (delay)
> > > usleep(delay);
> > > addr = msg.arg.pagefault.address;
> > > - r = handle_uffd_page_request(uffd, addr);
> > > + r = handle_uffd_page_request(uffd_args->uffd_mode, uffd, addr);
> > > if (r < 0)
> > > return NULL;
> > > pages++;
> > > @@ -201,17 +226,32 @@ static void *uffd_handler_thread_fn(void *arg)
> > >
> > > static int 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, uint64_t len)
> > > + void *hva, void *alias, uint64_t len)
> > > {
> > > int uffd;
> > > struct uffdio_api uffdio_api;
> > > struct uffdio_register uffdio_register;
> > > + uint64_t expected_ioctls = ((uint64_t) 1) << _UFFDIO_COPY;
> > > +
> > > + /* In order to get minor faults, prefault via the alias. */
> > > + if (uffd_mode == UFFDIO_REGISTER_MODE_MINOR) {
> > > + size_t p;
> > > +
> > > + expected_ioctls = ((uint64_t) 1) << _UFFDIO_CONTINUE;
> > > +
> > > + TEST_ASSERT(alias != NULL, "Alias required for minor faults");
> > > + for (p = 0; p < (len / demand_paging_size); ++p) {
> > > + memcpy(alias + (p * demand_paging_size),
> > > + guest_data_prototype, demand_paging_size);
> > > + }
> > > + }
> > >
> > > uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
> > > if (uffd == -1) {
> > > - pr_info("uffd creation failed\n");
> > > + pr_info("uffd creation failed, errno: %d\n", errno);
> > > return -1;
> > > }
> >
> > Huh, I wonder why I put all these return -1 statements in here. The
> > caller just does exit(-r) if r < 0. Seems like these could all just be
> > converted to TEST_ASSERTs.
>
> I agree that change makes sense, but it seems better to do it in a
> separate commit as it's maybe a 10-20 line change.
>
> Would you prefer I add that into this series, or just keep the status quo?
If you don't mind adding it to this series, that would be awesome.
>
> >
> > >
> > > @@ -224,18 +264,18 @@ static int setup_demand_paging(struct kvm_vm *vm,
> > >
> > > uffdio_register.range.start = (uint64_t)hva;
> > > uffdio_register.range.len = len;
> > > - uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
> > > + uffdio_register.mode = uffd_mode;
> > > if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register) == -1) {
> > > pr_info("ioctl uffdio_register failed\n");
> > > return -1;
> > > }
> > >
> > > - if ((uffdio_register.ioctls & UFFD_API_RANGE_IOCTLS) !=
> > > - UFFD_API_RANGE_IOCTLS) {
> > > - pr_info("unexpected userfaultfd ioctl set\n");
> > > + if ((uffdio_register.ioctls & expected_ioctls) != expected_ioctls) {
> > > + pr_info("missing userfaultfd ioctls\n");
> > > return -1;
> > > }
> > >
> > > + uffd_args->uffd_mode = uffd_mode;
> > > uffd_args->uffd = uffd;
> > > uffd_args->pipefd = pipefd;
> > > uffd_args->delay = uffd_delay;
> > > @@ -249,7 +289,7 @@ static int setup_demand_paging(struct kvm_vm *vm,
> > > }
> > >
> > > struct test_params {
> > > - bool use_uffd;
> > > + int uffd_mode;
> > > useconds_t uffd_delay;
> > > enum vm_mem_backing_src_type src_type;
> > > bool partition_vcpu_memory_access;
> > > @@ -286,7 +326,7 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> > > perf_test_setup_vcpus(vm, nr_vcpus, guest_percpu_mem_size,
> > > p->partition_vcpu_memory_access);
> > >
> > > - if (p->use_uffd) {
> > > + if (p->uffd_mode) {
> > > uffd_handler_threads =
> > > malloc(nr_vcpus * sizeof(*uffd_handler_threads));
> > > TEST_ASSERT(uffd_handler_threads, "Memory allocation failed");
> > > @@ -300,6 +340,7 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> > > for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++) {
> > > vm_paddr_t vcpu_gpa;
> > > void *vcpu_hva;
> > > + void *vcpu_alias;
> > > uint64_t vcpu_mem_size;
> > >
> > >
> > > @@ -314,8 +355,9 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> > > PER_VCPU_DEBUG("Added VCPU %d with test mem gpa [%lx, %lx)\n",
> > > vcpu_id, vcpu_gpa, vcpu_gpa + vcpu_mem_size);
> > >
> > > - /* Cache the HVA pointer of the region */
> > > + /* Cache the host addresses of the region */
> > > vcpu_hva = addr_gpa2hva(vm, vcpu_gpa);
> > > + vcpu_alias = addr_gpa2alias(vm, vcpu_gpa);
> > >
> > > /*
> > > * Set up user fault fd to handle demand paging
> > > @@ -327,9 +369,10 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> > >
> > > r = setup_demand_paging(vm,
> > > &uffd_handler_threads[vcpu_id],
> > > - pipefds[vcpu_id * 2],
> > > + pipefds[vcpu_id * 2], p->uffd_mode,
> > > p->uffd_delay, &uffd_args[vcpu_id],
> > > - vcpu_hva, vcpu_mem_size);
> > > + vcpu_hva, vcpu_alias,
> > > + vcpu_mem_size);
> > > if (r < 0)
> > > exit(-r);
> > > }
> > > @@ -359,7 +402,7 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> > >
> > > pr_info("All vCPU threads joined\n");
> > >
> > > - if (p->use_uffd) {
> > > + if (p->uffd_mode) {
> > > char c;
> > >
> > > /* Tell the user fault fd handler threads to quit */
> > > @@ -381,7 +424,7 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> > >
> > > free(guest_data_prototype);
> > > free(vcpu_threads);
> > > - if (p->use_uffd) {
> > > + if (p->uffd_mode) {
> > > free(uffd_handler_threads);
> > > free(uffd_args);
> > > free(pipefds);
> > > @@ -391,11 +434,11 @@ static void run_test(enum vm_guest_mode mode, void *arg)
> > > static void help(char *name)
> > > {
> > > puts("");
> > > - printf("usage: %s [-h] [-m mode] [-u] [-d uffd_delay_usec]\n"
> > > + printf("usage: %s [-h] [-m mode] [-u mode] [-d uffd_delay_usec]\n"
> > > " [-b memory] [-t type] [-v vcpus] [-o]\n", name);
> > > guest_modes_help();
> > > - printf(" -u: use User Fault FD to handle vCPU page\n"
> > > - " faults.\n");
> > > + printf(" -u: use userfaultfd to handle vCPU page faults. Mode is a\n"
> > > + " UFFD registration mode: 'MISSING' or 'MINOR'.\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");
> > > @@ -422,13 +465,17 @@ int main(int argc, char *argv[])
> > >
> > > guest_modes_append_default();
> > >
> > > - while ((opt = getopt(argc, argv, "hm:ud:b:t:v:o")) != -1) {
> > > + while ((opt = getopt(argc, argv, "hm:u:d:b:t:v:o")) != -1) {
> > > switch (opt) {
> > > case 'm':
> > > guest_modes_cmdline(optarg);
> > > break;
> > > case 'u':
> > > - p.use_uffd = true;
> > > + if (!strcmp("MISSING", optarg))
> > > + p.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'.");
> > > break;
> > > case 'd':
> > > p.uffd_delay = strtoul(optarg, NULL, 0);
> > > @@ -455,6 +502,9 @@ int main(int argc, char *argv[])
> > > }
> > > }
> > >
> > > + TEST_ASSERT(p.uffd_mode != UFFDIO_REGISTER_MODE_MINOR || p.src_type == VM_MEM_SRC_SHMEM,
> > > + "userfaultfd MINOR mode requires shared memory; pick a different -t");
> > > +
> > > for_each_guest_mode(run_test, &p);
> > >
> > > return 0;
> > > --
> > > 2.31.1.607.g51e8a6a459-goog
> > >
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