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    Subject[PATCH v4 06/10] userfaultfd/selftests: create alias mappings in the shmem test
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    Previously, we just allocated two shm areas: area_src and area_dst. With
    this commit, change this so we also allocate area_src_alias, and
    area_dst_alias.

    area_*_alias and area_* (respectively) point to the same underlying
    physical pages, but are different VMAs. In a future commit in this
    series, we'll leverage this setup to exercise minor fault handling
    support for shmem, just like we do in the hugetlb_shared test.

    Reviewed-by: Peter Xu <peterx@redhat.com>
    Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
    ---
    tools/testing/selftests/vm/userfaultfd.c | 22 +++++++++++++++++++---
    1 file changed, 19 insertions(+), 3 deletions(-)

    diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
    index fc40831f818f..1f65c4ab7994 100644
    --- a/tools/testing/selftests/vm/userfaultfd.c
    +++ b/tools/testing/selftests/vm/userfaultfd.c
    @@ -278,13 +278,29 @@ static void shmem_release_pages(char *rel_area)

    static void shmem_allocate_area(void **alloc_area)
    {
    - unsigned long offset =
    - alloc_area == (void **)&area_src ? 0 : nr_pages * page_size;
    + void *area_alias = NULL;
    + bool is_src = alloc_area == (void **)&area_src;
    + unsigned long offset = is_src ? 0 : nr_pages * page_size;

    *alloc_area = mmap(NULL, nr_pages * page_size, PROT_READ | PROT_WRITE,
    MAP_SHARED, shm_fd, offset);
    if (*alloc_area == MAP_FAILED)
    err("mmap of memfd failed");
    +
    + area_alias = mmap(NULL, nr_pages * page_size, PROT_READ | PROT_WRITE,
    + MAP_SHARED, shm_fd, offset);
    + if (area_alias == MAP_FAILED)
    + err("mmap of memfd alias failed");
    +
    + if (is_src)
    + area_src_alias = area_alias;
    + else
    + area_dst_alias = area_alias;
    +}
    +
    +static void shmem_alias_mapping(__u64 *start, size_t len, unsigned long offset)
    +{
    + *start = (unsigned long)area_dst_alias + offset;
    }

    struct uffd_test_ops {
    @@ -314,7 +330,7 @@ static struct uffd_test_ops shmem_uffd_test_ops = {
    .expected_ioctls = SHMEM_EXPECTED_IOCTLS,
    .allocate_area = shmem_allocate_area,
    .release_pages = shmem_release_pages,
    - .alias_mapping = noop_alias_mapping,
    + .alias_mapping = shmem_alias_mapping,
    };

    static struct uffd_test_ops hugetlb_uffd_test_ops = {
    --
    2.31.1.368.gbe11c130af-goog
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