Re: [RFC PATCH v2 0/7] Some improvement and a new test for kvm page table

[Ben Gardon]

On Wed, Feb 24, 2021 at 9:59 PM Yanan Wang <wangyanan55@xxxxxxxxxx> wrote:
>
> Hi,
> This v2 series can mainly include two parts.
> Based on kvm queue branch: https://git.kernel.org/pub/scm/virt/kvm/kvm.git/log/?h=queue
> Links of v1: https://lore.kernel.org/lkml/20210208090841.333724-1-wangyanan55@xxxxxxxxxx/
>
> In the first part, all the known hugetlb backing src types specified
> with different hugepage sizes are listed, so that we can specify use
> of hugetlb source of the exact granularity that we want, instead of
> the system default ones. And as all the known hugetlb page sizes are
> listed, it's appropriate for all architectures. Besides, a helper that
> can get granularity of different backing src types(anonumous/thp/hugetlb)
> is added, so that we can use the accurate backing src granularity for
> kinds of alignment or guest memory accessing of vcpus.
>
> In the second part, a new test is added:
> This test is added to serve as a performance tester and a bug reproducer
> for kvm page table code (GPA->HPA mappings), it gives guidance for the
> people trying to make some improvement for kvm. And the following explains
> what we can exactly do through this test.
>
> The function guest_code() can cover the conditions where a single vcpu or
> multiple vcpus access guest pages within the same memory region, in three
> VM stages(before dirty logging, during dirty logging, after dirty logging).
> Besides, the backing src memory type(ANONYMOUS/THP/HUGETLB) of the tested
> memory region can be specified by users, which means normal page mappings
> or block mappings can be chosen by users to be created in the test.
>
> If ANONYMOUS memory is specified, kvm will create normal page mappings
> for the tested memory region before dirty logging, and update attributes
> of the page mappings from RO to RW during dirty logging. If THP/HUGETLB
> memory is specified, kvm will create block mappings for the tested memory
> region before dirty logging, and split the blcok mappings into normal page
> mappings during dirty logging, and coalesce the page mappings back into
> block mappings after dirty logging is stopped.
>
> So in summary, as a performance tester, this test can present the
> performance of kvm creating/updating normal page mappings, or the
> performance of kvm creating/splitting/recovering block mappings,
> through execution time.
>
> When we need to coalesce the page mappings back to block mappings after
> dirty logging is stopped, we have to firstly invalidate *all* the TLB
> entries for the page mappings right before installation of the block entry,
> because a TLB conflict abort error could occur if we can't invalidate the
> TLB entries fully. We have hit this TLB conflict twice on aarch64 software
> implementation and fixed it. As this test can imulate process from dirty
> logging enabled to dirty logging stopped of a VM with block mappings,
> so it can also reproduce this TLB conflict abort due to inadequate TLB
> invalidation when coalescing tables.
>
> Links about the TLB conflict abort:
> https://lore.kernel.org/lkml/20201201201034.116760-3-wangyanan55@xxxxxxxxxx/

Besides a few style / readability comments, this series looks good to
me. Thanks for generalizing the way these selftests handle different
hugeTLB sizes!


>
> Yanan Wang (7):
>   tools include: sync head files of mmap flag encodings about hugetlb
>   KVM: selftests: Use flag CLOCK_MONOTONIC_RAW for timing
>   KVM: selftests: Make a generic helper to get vm guest mode strings
>   KVM: selftests: Add a helper to get system configured THP page size
>   KVM: selftests: List all hugetlb src types specified with page sizes
>   KVM: selftests: Adapt vm_userspace_mem_region_add to new helpers
>   KVM: selftests: Add a test for kvm page table code
>
>  tools/include/asm-generic/hugetlb_encode.h    |   3 +
>  tools/testing/selftests/kvm/Makefile          |   3 +
>  .../selftests/kvm/demand_paging_test.c        |   8 +-
>  .../selftests/kvm/dirty_log_perf_test.c       |  14 +-
>  .../testing/selftests/kvm/include/kvm_util.h  |   4 +-
>  .../testing/selftests/kvm/include/test_util.h |  21 +-
>  .../selftests/kvm/kvm_page_table_test.c       | 476 ++++++++++++++++++
>  tools/testing/selftests/kvm/lib/kvm_util.c    |  58 +--
>  tools/testing/selftests/kvm/lib/test_util.c   |  92 +++-
>  tools/testing/selftests/kvm/steal_time.c      |   4 +-
>  10 files changed, 623 insertions(+), 60 deletions(-)
>  create mode 100644 tools/testing/selftests/kvm/kvm_page_table_test.c
>
> --
> 2.19.1
>