Re: [PATCH v2 04/12] KVM: selftests: Require GPA to be aligned when backed by hugepages

[Ben Gardon <bgardon@google.com>]

On Wed, Nov 10, 2021 at 4:03 PM David Matlack <dmatlack@google.com> wrote:
>
> From: Sean Christopherson <seanjc@google.com>
>
> Assert that the GPA for a memslot backed by a hugepage is aligned to
> the hugepage size and fix perf_test_util accordingly.  Lack of GPA
> alignment prevents KVM from backing the guest with hugepages, e.g. x86's
> write-protection of hugepages when dirty logging is activated is
> otherwise not exercised.
>
> Add a comment explaining that guest_page_size is for non-huge pages to
> try and avoid confusion about what it actually tracks.
>
> Cc: Ben Gardon <bgardon@google.com>
> Cc: Yanan Wang <wangyanan55@huawei.com>
> Cc: Andrew Jones <drjones@redhat.com>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Aaron Lewis <aaronlewis@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> [Used get_backing_src_pagesz() to determine alignment dynamically.]
> Signed-off-by: David Matlack <dmatlack@google.com>
> ---
>  tools/testing/selftests/kvm/lib/kvm_util.c       | 2 ++
>  tools/testing/selftests/kvm/lib/perf_test_util.c | 7 ++++++-
>  2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 07f37456bba0..1f6a01c33dce 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -875,6 +875,8 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
>         if (src_type == VM_MEM_SRC_ANONYMOUS_THP)
>                 alignment = max(backing_src_pagesz, alignment);
>
> +       ASSERT_EQ(guest_paddr, align_up(guest_paddr, backing_src_pagesz));
> +
>         /* Add enough memory to align up if necessary */
>         if (alignment > 1)
>                 region->mmap_size += alignment;
> diff --git a/tools/testing/selftests/kvm/lib/perf_test_util.c b/tools/testing/selftests/kvm/lib/perf_test_util.c
> index 6b8d5020dc54..a015f267d945 100644
> --- a/tools/testing/selftests/kvm/lib/perf_test_util.c
> +++ b/tools/testing/selftests/kvm/lib/perf_test_util.c
> @@ -55,11 +55,16 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int vcpus,
>  {
>         struct kvm_vm *vm;
>         uint64_t guest_num_pages;
> +       uint64_t backing_src_pagesz = get_backing_src_pagesz(backing_src);
>         int i;
>
>         pr_info("Testing guest mode: %s\n", vm_guest_mode_string(mode));
>
>         perf_test_args.host_page_size = getpagesize();
> +       /*
> +        * Snapshot the non-huge page size.  This is used by the guest code to
> +        * access/dirty pages at the logging granularity.
> +        */
>         perf_test_args.guest_page_size = vm_guest_mode_params[mode].page_size;

Is this comment correct? I wouldn't expect the guest page size to
determine the host dirty logging granularity.

>
>         guest_num_pages = vm_adjust_num_guest_pages(mode,
> @@ -92,7 +97,7 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int vcpus,
>
>         guest_test_phys_mem = (vm_get_max_gfn(vm) - guest_num_pages) *
>                               perf_test_args.guest_page_size;
> -       guest_test_phys_mem = align_down(guest_test_phys_mem, perf_test_args.host_page_size);
> +       guest_test_phys_mem = align_down(guest_test_phys_mem, backing_src_pagesz);
>  #ifdef __s390x__
>         /* Align to 1M (segment size) */
>         guest_test_phys_mem = align_down(guest_test_phys_mem, 1 << 20);
> --
> 2.34.0.rc1.387.gb447b232ab-goog
>