Re: [PATCH v8 38/46] KVM: selftests: Add helpers to pin pages with CONFIG_GUP_TEST

[Fuad Tabba]

On Fri, 19 Jun 2026 at 01:32, Ackerley Tng via B4 Relay
<devnull+ackerleytng.google.com@xxxxxxxxxx> wrote:
>
> From: Ackerley Tng <ackerleytng@xxxxxxxxxx>
>
> Add helper functions to allow KVM selftests to pin memory using
> CONFIG_GUP_TEST. This is useful for testing scenarios where some page has
> an increased refcount. such as in guest_memfd in-place conversion tests.
>
> The helpers open /sys/kernel/debug/gup_test and invoke the
> PIN_LONGTERM_TEST_START and PIN_LONGTERM_TEST_STOP ioctls. Since this
> functionality depends on the kernel being built with CONFIG_GUP_TEST,
> provide stub implementations that trigger a test failure if the
> configuration is missing.
>
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>

nit below, otherwise:

Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>

Cheers,
/fuad

> ---
>  tools/testing/selftests/kvm/include/kvm_util.h |  3 +++
>  tools/testing/selftests/kvm/lib/kvm_util.c     | 23 +++++++++++++++++++++++
>  2 files changed, 26 insertions(+)
>
> diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> index 323d06b5699ec..79ab64ac8b869 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> @@ -1195,6 +1195,9 @@ static inline int pin_self_to_any_cpu(void)
>         return pin_task_to_any_cpu(pthread_self());
>  }
>
> +void pin_pages(void *vaddr, uint64_t size);
> +void unpin_pages(void);
> +
>  void kvm_print_vcpu_pinning_help(void);
>  void kvm_parse_vcpu_pinning(const char *pcpus_string, u32 vcpu_to_pcpu[],
>                             int nr_vcpus);
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index b73817f7bc803..524ef97d634bf 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -18,6 +18,8 @@
>  #include <unistd.h>
>  #include <linux/kernel.h>
>
> +#include "../../../../mm/gup_test.h"
> +
>  #define KVM_UTIL_MIN_PFN       2
>
>  u32 guest_random_seed;
> @@ -639,6 +641,27 @@ int __pin_task_to_cpu(pthread_t task, int cpu)
>         return pthread_setaffinity_np(task, sizeof(cpuset), &cpuset);
>  }
>
> +static int gup_test_fd = -1;
> +
> +void pin_pages(void *vaddr, uint64_t size)
> +{
> +       const struct pin_longterm_test args = {
> +               .addr = (uint64_t)vaddr,
> +               .size = size,
> +               .flags = PIN_LONGTERM_TEST_FLAG_USE_WRITE,
> +       };
> +
> +       gup_test_fd = __open_path_or_exit("/sys/kernel/debug/gup_test", O_RDWR,
> +                                         "Is CONFIG_GUP_TEST enabled?");

nit: should you close this/reset it to -1 after the tests?

> +
> +       TEST_ASSERT_EQ(ioctl(gup_test_fd, PIN_LONGTERM_TEST_START, &args), 0);
> +}
> +
> +void unpin_pages(void)
> +{
> +       TEST_ASSERT_EQ(ioctl(gup_test_fd, PIN_LONGTERM_TEST_STOP), 0);
> +}
> +
>  static u32 parse_pcpu(const char *cpu_str, const cpu_set_t *allowed_mask)
>  {
>         u32 pcpu = atoi_non_negative("CPU number", cpu_str);
>
> --
> 2.55.0.rc0.738.g0c8ab3ebcc-goog
>
>