linux-kernel - Re: [PATCH v2 07/10] KVM: selftests: add shmem backing source type

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Date:   Wed, 19 May 2021 15:03:45 -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 v2 07/10] KVM: selftests: add shmem backing source type

On Wed, May 19, 2021 at 1:04 PM Axel Rasmussen <axelrasmussen@...gle.com> wrote:
>
> This lets us run the demand paging test on top of a shmem-backed area.
> In follow-up commits, we'll 1) leverage this new capability to create an
> alias mapping, and then 2) use the alias mapping to exercise UFFD minor
> faults.
>
> Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>
> ---
>  tools/testing/selftests/kvm/include/test_util.h |  1 +
>  tools/testing/selftests/kvm/lib/kvm_util.c      | 15 +++++++++++++++
>  tools/testing/selftests/kvm/lib/test_util.c     |  5 +++++
>  3 files changed, 21 insertions(+)
>
> diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h
> index fade3130eb01..7377f00469ef 100644
> --- a/tools/testing/selftests/kvm/include/test_util.h
> +++ b/tools/testing/selftests/kvm/include/test_util.h
> @@ -84,6 +84,7 @@ enum vm_mem_backing_src_type {
>         VM_MEM_SRC_ANONYMOUS_HUGETLB_1GB,
>         VM_MEM_SRC_ANONYMOUS_HUGETLB_2GB,
>         VM_MEM_SRC_ANONYMOUS_HUGETLB_16GB,
> +       VM_MEM_SRC_SHMEM,
>         NUM_SRC_TYPES,
>  };
>
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index bc405785ac8b..e4a8d0c43c5e 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -757,6 +757,21 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
>         if (alignment > 1)
>                 region->mmap_size += alignment;
>
> +       region->fd = -1;

Ah I guess this is the corresponding change from the previous patch.

> +       if (src_type == VM_MEM_SRC_SHMEM) {
> +               region->fd = memfd_create("kvm_selftest", MFD_CLOEXEC);
> +               TEST_ASSERT(region->fd != -1,
> +                           "memfd_create failed, errno: %i", errno);
> +
> +               ret = ftruncate(region->fd, region->mmap_size);
> +               TEST_ASSERT(ret == 0, "ftruncate failed, errno: %i", errno);
> +
> +               ret = fallocate(region->fd,
> +                               FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, 0,
> +                               region->mmap_size);
> +               TEST_ASSERT(ret == 0, "fallocate failed, errno: %i", errno);
> +       }
> +
>         region->mmap_start = mmap(NULL, region->mmap_size,
>                                   PROT_READ | PROT_WRITE,
>                                   vm_mem_backing_src_alias(src_type)->flag,
> diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c
> index 06ddde068736..c7a265da5090 100644
> --- a/tools/testing/selftests/kvm/lib/test_util.c
> +++ b/tools/testing/selftests/kvm/lib/test_util.c
> @@ -236,6 +236,10 @@ const struct vm_mem_backing_src_alias *vm_mem_backing_src_alias(uint32_t i)
>                         .name = "anonymous_hugetlb_16gb",
>                         .flag = anon_huge_flags | MAP_HUGE_16GB,
>                 },
> +               [VM_MEM_SRC_SHMEM] = {
> +                       .name = "shmem",
> +                       .flag = MAP_SHARED,
> +               },
>         };
>         _Static_assert(ARRAY_SIZE(aliases) == NUM_SRC_TYPES,
>                        "Missing new backing src types?");
> @@ -253,6 +257,7 @@ size_t get_backing_src_pagesz(uint32_t i)
>
>         switch (i) {
>         case VM_MEM_SRC_ANONYMOUS:
> +       case VM_MEM_SRC_SHMEM:
>                 return getpagesize();
>         case VM_MEM_SRC_ANONYMOUS_THP:
>                 return get_trans_hugepagesz();
> --
> 2.31.1.751.gd2f1c929bd-goog
>