linux-kernel - Re: KVM selftests are failing

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Message-ID: <87efbmqore.fsf@vitty.brq.redhat.com>
Date:   Thu, 15 Nov 2018 17:39:01 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Ahmed Soliman <ahmedsoliman@...a.vt.edu>
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>, linux-kernel@...r.kernel.org,
        Andrew Jones <drjones@...hat.com>
Subject: Re: KVM selftests are failing

Ahmed Soliman <ahmedsoliman@...a.vt.edu> writes:

> 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()

Just ignore -EINVAL returned from madvise(), QEMU went even further,
see:

commit 1d7414396f926651c4d7a673eb3a10aca5246d76
Author: Dr. David Alan Gilbert <dgilbert@...hat.com>
Date:   Thu Nov 19 15:27:48 2015 +0000

    Assume madvise for (no)hugepage works

-- 
Vitaly