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From:   Paolo Bonzini <pbonzini@redhat.com>
Date:   Wed, 15 Mar 2023 13:24:25 +0100
Message-ID: <CABgObfYm6roWVR0myT5rHUWRe7k09TkXgZ7rYAr019QZ80oQXQ@mail.gmail.com>
Subject: Re: [PATCH V5 0/2] selftests: KVM: Add a test for eager page splitting
To:     David Matlack <dmatlack@google.com>
Cc:     Ben Gardon <bgardon@google.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, Peter Xu <peterx@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vipin Sharma <vipinsh@google.com>,
        Ricardo Koller <ricarkol@google.com>
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On Tue, Mar 14, 2023 at 5:00=E2=80=AFPM David Matlack <dmatlack@google.com>=
 wrote:
> On Tue, Mar 14, 2023 at 7:23=E2=80=AFAM Paolo Bonzini <pbonzini@redhat.co=
m> wrote:
> > $ 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)
> > =3D=3D=3D=3D Test Assertion Failure =3D=3D=3D=3D
> >   x86_64/dirty_log_page_splitting_test.c:195: __a =3D=3D __b
> >   pid=3D1378203 tid=3D1378203 errno=3D0 - 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:2=
45
> >      4    0x00007f4227c3feaf: ?? ??:0
> >      5    0x00007f4227c3ff5f: ?? ??:0
> >      6    0x0000000000402594: _start at ??:?
> >   ASSERT_EQ(stats_populated.pages_4k, stats_repopulated.pages_4k) faile=
d.
> >     stats_populated.pages_4k is 0x413
> >     stats_repopulated.pages_4k is 0x412
>
> 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.

I don't think so, it's 100% reproducible and the machine is idle and
only accessed via network. Also has 64 GB of RAM. :)

Paolo