Re: [PATCH 4/4] selftests: KVM: use dirty logging to check if page stats work correctly

[Ben Gardon]

On Sun, Mar 20, 2022 at 5:26 PM Mingwei Zhang <mizhang@xxxxxxxxxx> wrote:
>
> When dirty logging is enabled, KVM splits the all hugepage mapping in
> NPT/EPT into the smallest 4K size. This property could be used to check if
> the page stats metrics work properly in KVM mmu. At the same time, this
> logic might be used the other way around: using page stats to verify if
> dirty logging really splits all huge pages. Moreover, when dirty logging is
> disabled, KVM zaps corresponding SPTEs and we could check whether the large
> pages come back when guest touches the pages again.
>
> So add page stats checking in dirty logging performance selftest. In
> particular, add checks in three locations:
>  - just after vm is created;
>  - after populating memory into vm but before enabling dirty logging;
>  - just after turning on dirty logging.
>  - after one final iteration after turning off dirty logging.
>
> Tested using commands:
>  - ./dirty_log_perf_test -s anonymous_hugetlb_1gb
>  - ./dirty_log_perf_test -s anonymous_thp
>
> Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
> Cc: David Matlack <dmatlack@xxxxxxxxxx>
> Cc: Jing Zhang <jingzhangos@xxxxxxxxxx>
> Cc: Peter Xu <peterx@xxxxxxxxxx>
>
> Suggested-by: Ben Gardon <bgorden@xxxxxxxxxx>

Woops, got a mail bounce from this. Should be:
Suggested-by: Ben Gardon <bgardon@xxxxxxxxxx>

> Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
> ---
>  .../selftests/kvm/dirty_log_perf_test.c       | 52 +++++++++++++++++++
>  1 file changed, 52 insertions(+)
>
> diff --git a/tools/testing/selftests/kvm/dirty_log_perf_test.c b/tools/testing/selftests/kvm/dirty_log_perf_test.c
> index 1954b964d1cf..ab0457d91658 100644
> --- a/tools/testing/selftests/kvm/dirty_log_perf_test.c
> +++ b/tools/testing/selftests/kvm/dirty_log_perf_test.c
> @@ -19,6 +19,10 @@
>  #include "perf_test_util.h"
>  #include "guest_modes.h"
>
> +#ifdef __x86_64__
> +#include "processor.h"
> +#endif
> +
>  /* How many host loops to run by default (one KVM_GET_DIRTY_LOG for each loop)*/
>  #define TEST_HOST_LOOP_N               2UL
>
> @@ -185,6 +189,14 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>                                  p->slots, p->backing_src,
>                                  p->partition_vcpu_memory_access);
>
> +#ifdef __x86_64__
> +       TEST_ASSERT(vm_get_single_stat(vm, "pages_4k") == 0,
> +                   "4K page is non zero");
> +       TEST_ASSERT(vm_get_single_stat(vm, "pages_2m") == 0,
> +                   "2M page is non zero");
> +       TEST_ASSERT(vm_get_single_stat(vm, "pages_1g") == 0,
> +                   "1G page is non zero");
> +#endif
>         perf_test_set_wr_fract(vm, p->wr_fract);
>
>         guest_num_pages = (nr_vcpus * guest_percpu_mem_size) >> vm_get_page_shift(vm);
> @@ -222,6 +234,16 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>         pr_info("Populate memory time: %ld.%.9lds\n",
>                 ts_diff.tv_sec, ts_diff.tv_nsec);
>
> +#ifdef __x86_64__
> +       TEST_ASSERT(vm_get_single_stat(vm, "pages_4k") != 0,
> +                   "4K page is zero");
> +       if (p->backing_src == VM_MEM_SRC_ANONYMOUS_THP)
> +               TEST_ASSERT(vm_get_single_stat(vm, "pages_2m") != 0,
> +                           "2M page is zero");
> +       if (p->backing_src == VM_MEM_SRC_ANONYMOUS_HUGETLB_1GB)
> +               TEST_ASSERT(vm_get_single_stat(vm, "pages_1g") != 0,
> +                           "1G page is zero");
> +#endif
>         /* Enable dirty logging */
>         clock_gettime(CLOCK_MONOTONIC, &start);
>         enable_dirty_logging(vm, p->slots);
> @@ -267,6 +289,14 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>                                 iteration, ts_diff.tv_sec, ts_diff.tv_nsec);
>                 }
>         }
> +#ifdef __x86_64__
> +       TEST_ASSERT(vm_get_single_stat(vm, "pages_4k") != 0,
> +                   "4K page is zero after dirty logging");
> +       TEST_ASSERT(vm_get_single_stat(vm, "pages_2m") == 0,
> +                   "2M page is non-zero after dirty logging");
> +       TEST_ASSERT(vm_get_single_stat(vm, "pages_1g") == 0,
> +                   "1G page is non-zero after dirty logging");
> +#endif
>
>         /* Disable dirty logging */
>         clock_gettime(CLOCK_MONOTONIC, &start);
> @@ -275,6 +305,28 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>         pr_info("Disabling dirty logging time: %ld.%.9lds\n",
>                 ts_diff.tv_sec, ts_diff.tv_nsec);
>
> +#ifdef __x86_64__
> +       /*
> +        * Increment iteration to run the vcpus again to verify if huge pages
> +        * come back.
> +        */
> +       iteration++;
> +       pr_info("Starting the final iteration to verify page stats\n");
> +
> +       for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++) {
> +               while (READ_ONCE(vcpu_last_completed_iteration[vcpu_id])
> +                      != iteration)
> +                       ;
> +       }
> +
> +       if (p->backing_src == VM_MEM_SRC_ANONYMOUS_THP)
> +               TEST_ASSERT(vm_get_single_stat(vm, "pages_2m") != 0,
> +                           "2M page is zero");
> +       if (p->backing_src == VM_MEM_SRC_ANONYMOUS_HUGETLB_1GB)
> +               TEST_ASSERT(vm_get_single_stat(vm, "pages_1g") != 0,
> +                           "1G page is zero");
> +#endif
> +
>         /* Tell the vcpu thread to quit */
>         host_quit = true;
>         perf_test_join_vcpu_threads(nr_vcpus);
> --
> 2.35.1.894.gb6a874cedc-goog
>