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

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Message-ID: <CABgObfYm6roWVR0myT5rHUWRe7k09TkXgZ7rYAr019QZ80oQXQ@mail.gmail.com>
Date:   Wed, 15 Mar 2023 13:24:25 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Matlack <dmatlack@...gle.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 5:00 PM David Matlack <dmatlack@...gle.com> wrote:
> On Tue, Mar 14, 2023 at 7:23 AM Paolo Bonzini <pbonzini@...hat.com> 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)
> > ==== 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
>
> 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