Re: [PATCH 1/2] selftests/kvm: Setup vcpu_alias only for minor mode test

[James Houghton]

On Thu, Apr 27, 2023 at 1:11 PM Peter Xu <peterx@xxxxxxxxxx> wrote:
>
> This fixes two things:
>
> - Unbreaks MISSING mode test on anonymous memory type
>
> - Prefault alias mem before uffd thread creations, otherwise the uffd
>   thread timing will be inaccurate when guest mem size is large, because
>   it'll take prefault time into total time.
>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>

Reviewed-by: James Houghton <jthoughton@xxxxxxxxxx>

FWIW, it looks like this fixes this commit[1]. Not sure if it's worth
a Fixes: tag.

[1]: commit a93871d0ea9f ("KVM: selftests: Add a userfaultfd library")


> ---
>  .../testing/selftests/kvm/demand_paging_test.c  | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c
> index 2439c4043fed..9c18686b4f63 100644
> --- a/tools/testing/selftests/kvm/demand_paging_test.c
> +++ b/tools/testing/selftests/kvm/demand_paging_test.c
> @@ -128,6 +128,7 @@ static void prefault_mem(void *alias, uint64_t len)
>
>  static void run_test(enum vm_guest_mode mode, void *arg)
>  {
> +       struct memstress_vcpu_args *vcpu_args;
>         struct test_params *p = arg;
>         struct uffd_desc **uffd_descs = NULL;
>         struct timespec start;
> @@ -145,24 +146,24 @@ 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 == UFFDIO_REGISTER_MODE_MINOR) {
> +               for (i = 0; i < nr_vcpus; i++) {
> +                       vcpu_args = &memstress_args.vcpu_args[i];
> +                       prefault_mem(addr_gpa2alias(vm, vcpu_args->gpa),
> +                                    vcpu_args->pages * memstress_args.guest_page_size);
> +               }
> +       }
> +
>         if (p->uffd_mode) {
>                 uffd_descs = malloc(nr_vcpus * sizeof(struct uffd_desc *));
>                 TEST_ASSERT(uffd_descs, "Memory allocation failed");
> -
>                 for (i = 0; i < nr_vcpus; i++) {
> -                       struct memstress_vcpu_args *vcpu_args;
>                         void *vcpu_hva;
> -                       void *vcpu_alias;
>
>                         vcpu_args = &memstress_args.vcpu_args[i];
>
>                         /* Cache the host addresses of the region */
>                         vcpu_hva = addr_gpa2hva(vm, vcpu_args->gpa);
> -                       vcpu_alias = addr_gpa2alias(vm, vcpu_args->gpa);
> -
> -                       prefault_mem(vcpu_alias,
> -                               vcpu_args->pages * memstress_args.guest_page_size);
> -
>                         /*
>                          * Set up user fault fd to handle demand paging
>                          * requests.
> --
> 2.39.1
>