linux-kernel - [PATCH V5 0/2] selftests: KVM: Add a test for eager page splitting

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Message-ID: <20230131181820.179033-1-bgardon@google.com>
Date:   Tue, 31 Jan 2023 18:18:18 +0000
From:   Ben Gardon <bgardon@...gle.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Vipin Sharma <vipinsh@...gle.com>,
        Ricardo Koller <ricarkol@...gle.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH V5 0/2] selftests: KVM: Add a test for eager page splitting

David Matlack recently added a feature known as eager page splitting
to x86 KVM. This feature improves vCPU performance during dirty
logging because the splitting operation is moved out of the page
fault path, avoiding EPT/NPT violations or allowing the vCPU threads
to resolve the violation in the fast path.

While this feature is a great performance improvement, it does not
have adequate testing in KVM selftests. Add a test to provide coverage
of eager page splitting.

Patch 1 is a quick refactor to be able to re-use some code from
dirty_log_perf_test.
Patch 2 adds the actual test.

V4->V5:
 - V4: https://lore.kernel.org/all/Y9lIfGtMEEsaw6cd@google.com/
 - Separated a helper function to just run vCPUs for an iteration and
   not also collect the stats. Suggested by Vipin.
 - Added a log message when the host does not support MANUAL_PROTECT,
   and so testing with that capability is skipped. Also suggested by
   Vipin.
 - Added RB from Vipin.

V3->V4:
 - Added the copyright notices back. Thanks Vipin for the right
   thing to do there.

V2->V3:
 - Removed copyright notice from the top of dirty_log_page_splitting.c
 - Adopted ASSERT_EQ for test assertions
 - Now skipping testing with MANUAL_PROTECT if unsupported

V1->V2:
 - Run test in multiple modes, as suggested by David and Ricardo
 - Cleanups from shameful copy-pasta, as suggested by David

Ben Gardon (2):
  selftests: KVM: Move dirty logging functions to memstress.(c|h)
  selftests: KVM: Add dirty logging page splitting test

 tools/testing/selftests/kvm/Makefile          |   1 +
 .../selftests/kvm/dirty_log_perf_test.c       |  84 +-----
 .../selftests/kvm/include/kvm_util_base.h     |   1 +
 .../testing/selftests/kvm/include/memstress.h |   8 +
 tools/testing/selftests/kvm/lib/kvm_util.c    |   5 +
 tools/testing/selftests/kvm/lib/memstress.c   |  72 +++++
 .../x86_64/dirty_log_page_splitting_test.c    | 260 ++++++++++++++++++
 7 files changed, 354 insertions(+), 77 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/x86_64/dirty_log_page_splitting_test.c

-- 
2.39.1.456.gfc5497dd1b-goog