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

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Date:   Tue, 14 Mar 2023 09:00:28 -0700
From:   David Matlack <dmatlack@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Ben Gardon <bgardon@...gle.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vipin Sharma <vipinsh@...gle.com>,
        Ricardo Koller <ricarkol@...gle.com>
Subject: Re: [PATCH V5 0/2] selftests: KVM: Add a test for eager page splitting

On Tue, Mar 14, 2023 at 7:23 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On Tue, Mar 14, 2023 at 2:27 PM Paolo Bonzini <pbonzini@...hat.com> wrote:
> > I have finally queued it, but made a small change to allow running it
> > with non-hugetlbfs page types.
>
> Oops, it fails on my AMD workstation:
>
> $ tools/testing/selftests/kvm/x86_64/dirty_log_page_splitting_test
> Testing guest mode: PA-bits:ANY, VA-bits:48,  4K pages
> guest physical test memory: [0x7fc7fe00000, 0x7fcffe00000)
> ==== Test Assertion Failure ====
>   x86_64/dirty_log_page_splitting_test.c:195: __a == __b
>   pid=1378203 tid=1378203 errno=0 - Success
>      1    0x0000000000402d02: run_test at dirty_log_page_splitting_test.c:195
>      2    0x000000000040367c: for_each_guest_mode at guest_modes.c:100
>      3    0x00000000004024df: main at dirty_log_page_splitting_test.c:245
>      4    0x00007f4227c3feaf: ?? ??:0
>      5    0x00007f4227c3ff5f: ?? ??:0
>      6    0x0000000000402594: _start at ??:?
>   ASSERT_EQ(stats_populated.pages_4k, stats_repopulated.pages_4k) failed.
>     stats_populated.pages_4k is 0x413
>     stats_repopulated.pages_4k is 0x412
>
> Haven't debugged it yet.

I wonder if pages are getting swapped, especially if running on a
workstation. If so, mlock()ing all guest memory VMAs might be
necessary to be able to assert exact page counts.

>
> Paolo
>