linux-kernel - Re: [PATCH v2 04/10] KVM: selftests: compute correct demand paging size

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Date:   Wed, 19 May 2021 14:51:41 -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 04/10] KVM: selftests: compute correct demand paging size

On Wed, May 19, 2021 at 1:03 PM Axel Rasmussen <axelrasmussen@...gle.com> wrote:
>
> This is a preparatory commit needed before we can use different kinds of
> backing pages for guest memory.
>
> Previously, we used perf_test_args.host_page_size, which is the host's
> native page size (commonly 4K). For VM_MEM_SRC_ANONYMOUS this turns out
> to be okay, but in a follow-up commit we want to allow using different
> kinds of backing memory.
>
> Take VM_MEM_SRC_ANONYMOUS_HUGETLB for example. Without this change, if
> we used that backing page type, when we issued a UFFDIO_COPY ioctl we'd
> only do so with 4K, rather than the full 2M of a backing hugepage. In
> this case, UFFDIO_COPY returns -EINVAL (__mcopy_atomic_hugetlb checks
> the size).
>
> Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>

Reviewed-by: Ben Gardon <bgardon@...gle.com>

> ---
>  tools/testing/selftests/kvm/demand_paging_test.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c
> index 601a1df24dd2..94cf047358d5 100644
> --- a/tools/testing/selftests/kvm/demand_paging_test.c
> +++ b/tools/testing/selftests/kvm/demand_paging_test.c
> @@ -40,6 +40,7 @@
>
>  static int nr_vcpus = 1;
>  static uint64_t guest_percpu_mem_size = DEFAULT_PER_VCPU_MEM_SIZE;
> +static size_t demand_paging_size;
>  static char *guest_data_prototype;
>
>  static void *vcpu_worker(void *data)
> @@ -85,7 +86,7 @@ static int handle_uffd_page_request(int uffd, uint64_t addr)
>
>         copy.src = (uint64_t)guest_data_prototype;
>         copy.dst = addr;
> -       copy.len = perf_test_args.host_page_size;
> +       copy.len = demand_paging_size;
>         copy.mode = 0;
>
>         clock_gettime(CLOCK_MONOTONIC, &start);
> @@ -102,7 +103,7 @@ static int handle_uffd_page_request(int uffd, uint64_t addr)
>         PER_PAGE_DEBUG("UFFDIO_COPY %d \t%ld ns\n", tid,
>                        timespec_to_ns(ts_diff));
>         PER_PAGE_DEBUG("Paged in %ld bytes at 0x%lx from thread %d\n",
> -                      perf_test_args.host_page_size, addr, tid);
> +                      demand_paging_size, addr, tid);
>
>         return 0;
>  }
> @@ -261,10 +262,12 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>
>         perf_test_args.wr_fract = 1;
>
> -       guest_data_prototype = malloc(perf_test_args.host_page_size);
> +       demand_paging_size = get_backing_src_pagesz(VM_MEM_SRC_ANONYMOUS);
> +
> +       guest_data_prototype = malloc(demand_paging_size);
>         TEST_ASSERT(guest_data_prototype,
>                     "Failed to allocate buffer for guest data pattern");
> -       memset(guest_data_prototype, 0xAB, perf_test_args.host_page_size);
> +       memset(guest_data_prototype, 0xAB, demand_paging_size);
>
>         vcpu_threads = malloc(nr_vcpus * sizeof(*vcpu_threads));
>         TEST_ASSERT(vcpu_threads, "Memory allocation failed");
> --
> 2.31.1.751.gd2f1c929bd-goog
>