linux-kernel - Re: [PATCH 05/15] KVM: selftests: Require GPA to be aligned when backed by hugepages

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Date:   Wed, 10 Feb 2021 17:01:58 -0800
From:   Ben Gardon <bgardon@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Yanan Wang <wangyanan55@...wei.com>,
        Andrew Jones <drjones@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Aaron Lewis <aaronlewis@...gle.com>
Subject: Re: [PATCH 05/15] KVM: selftests: Require GPA to be aligned when
 backed by hugepages

On Wed, Feb 10, 2021 at 3:06 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Assert that the GPA for a memslot backed by a hugepage is 1gb aligned,
> 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@...gle.com>
> Cc: Yanan Wang <wangyanan55@...wei.com>
> Cc: Andrew Jones <drjones@...hat.com>
> Cc: Peter Xu <peterx@...hat.com>
> Cc: Aaron Lewis <aaronlewis@...gle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  tools/testing/selftests/kvm/lib/kvm_util.c       | 2 ++
>  tools/testing/selftests/kvm/lib/perf_test_util.c | 9 +++++++++
>  2 files changed, 11 insertions(+)
>
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 2e497fbab6ae..855d20784ba7 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -735,6 +735,8 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
>         else
>                 ASSERT_EQ(src_type, VM_MEM_SRC_ANONYMOUS);
>
> +       ASSERT_EQ(guest_paddr, align(guest_paddr, alignment));
> +
>         /* 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 81490b9b4e32..f187b86f2e14 100644
> --- a/tools/testing/selftests/kvm/lib/perf_test_util.c
> +++ b/tools/testing/selftests/kvm/lib/perf_test_util.c
> @@ -58,6 +58,11 @@ struct kvm_vm *perf_test_create_vm(enum vm_guest_mode mode, int vcpus,
>         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;
>
>         guest_num_pages = vm_adjust_num_guest_pages(mode,
> @@ -87,6 +92,10 @@ 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 &= ~(perf_test_args.host_page_size - 1);
> +       if (backing_src == VM_MEM_SRC_ANONYMOUS_THP ||
> +           backing_src == VM_MEM_SRC_ANONYMOUS_HUGETLB)
> +               guest_test_phys_mem &= ~(KVM_UTIL_HUGEPAGE_ALIGNMENT - 1);

You could use the align helper here as well. That would make this a
little easier for me to read.

> +
>  #ifdef __s390x__
>         /* Align to 1M (segment size) */
>         guest_test_phys_mem &= ~((1 << 20) - 1);
> --
> 2.30.0.478.g8a0d178c01-goog
>