linux-kernel - Re: Major KVM issues with kernel 4.5 on the host

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Message-ID: <20160421145005.GI21755@torres.zugschlus.de>
Date:	Thu, 21 Apr 2016 16:50:05 +0200
From:	Marc Haber <mh+linux-kernel@...schlus.de>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm ML <kvm@...r.kernel.org>
Subject: Re: Major KVM issues with kernel 4.5 on the host

On Thu, Apr 21, 2016 at 02:37:11PM +0200, Borislav Petkov wrote:
> On Thu, Apr 21, 2016 at 10:39:48AM +0200, Marc Haber wrote:
> > Currently, I cannot explain how this has happened, I must have flagged
> > an actually good kernel as bad from my understanding of git bisect.
> > 
> > Can you give advice how to continue here?
> 
> Yap, sounds like you marked a bisection step incorrectly, which lead
> into the wrong direction. How reliable is your reproducer?

Usually, the crash or filesystem corruption happens in the first 15 to
30 minutes. I have had one instance running three hours before
corrupting, I have therefore upped the run time to nine hours before
saying "this kernel is good".

What bothers me is that since I ended up with a "suspect" commit that
actually results in a "good" kernel (running for 22 hours now), I must
have said "bad" to an actually "good" kernel, which means that I had
an unrelated crash or corruption. Is that reasoning correct?

> Also, do the bisection as Paolo suggested:
> 
> * try 45bdbcfdf241.

That one qualified as "good" six days ago. I'll retry, maybe I just
didn't wait long enough.

"Trying" means make oldconfig, make deb-pkg in my case right? Does it
matter what I answer to the numerous config questions that keep coming
up during the oldconfig step?

> * then do
> 
> $ git bisect start v4.5-rc1 v4.4
> 
> which marks -rc1 as bad and 4.4 as good.

Would it help to explicitly mark
0e749e54244eec87b2a3cd0a4314e60bc6781115 as good so that the knowledge
gained during the last week is not completely lost?

> While you're doing that bisect, do what Paolo said by applying the diff
> here
> 
>   https://lkml.kernel.org/r/570EADD2.8030300@redhat.com
> 
> when the bisection point you're at at each step contains
> 
>   46896c73c1a4 ("KVM: svm: add support for RDTSCP")
> 
> You should apply the above hunk by doing
> 
> $ patch -p1 --dry-run -i /tmp/hunk
> 
> If it applies fine, you then apply it
> 
> $ patch -p1 -i /tmp/hunk
> 
> All clear?

So I need to git log | grep 46896c73c1a4 and apply the patch again
each time the commit is found?

Greetings
Marc

-- 
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