linux-kernel - Re: KVM selftests are failing

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Date:   Thu, 15 Nov 2018 18:15:22 +0200
From:   Ahmed Soliman <ahmedsoliman@...a.vt.edu>
To:     Andrew Jones <drjones@...hat.com>
Cc:     Anders Roxell <anders.roxell@...aro.org>,
        Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: KVM selftests are failing

Hello,
On Thu, Nov 15, 2018 at 4:50 PM Andrew Jones <drjones@...hat.com> wrote:
>
> On Thu, Nov 15, 2018 at 03:36:44PM +0200, Ahmed Soliman wrote:
> > mmap(NULL, 6291456, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
> > -1, 0) = 0x7f46ea2a1000
> > madvise(0x7f46ea2a1000, 6291456, MADV_NOHUGEPAGE) = -1 EINVAL (Invalid argument)
> >
> > For comprehension, this is done on intel core i7-4500U CPU @ 1.80GHz
>
> Argh. I see what it is. Your config doesn't have CONFIG_TRANSPARENT_HUGEPAGE=y,
> so madvise_behavior_valid() returns false, which causes madvise() to
> immediately return EINVAL. We should be more careful in kvm selftests with
> our madvise behavior use.
>
> >
> > As for now I will comment the madvise line and the assert when writing
> > my own kvm self test. I think it wouldn't cause any trouble?, If it is
> > not the case, please let me know.
> >
>
> You may not need madvise() at all for your test, depending on what you're
> doing. So leaving it out may be fine. Reworking kvm selftests to ensure
> only valid madvise behaviors are used (and only when necessary), before
> adding new tests, would be best.

Confirmed it worked after CONFIG_TRANSPARENT_HUGEPAGE=y
I will send a patch soon that should make the self test check if
Transparent huge pages are enabled first before issuing the related
madvise()

Thanks,
-- 
Ahmed,
Junior Researcher, IoT and Cyber Security lab, SmartCI, Alexandria
University, & CIS @  VMI