linux-kernel - Re: [GIT PULL] First batch of KVM changes for 4.1

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Message-ID: <55380C3D.2080906@redhat.com>
Date:	Wed, 22 Apr 2015 23:01:49 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	gleb@...nel.org, kvm@...r.kernel.org,
	Ralf Baechle <ralf@...ux-mips.org>, luto@...nel.org
Subject: Re: [GIT PULL] First batch of KVM changes for 4.1

On 22/04/2015 22:56, Marcelo Tosatti wrote:
>> > But then why was the task migration notifier even in Jeremy's original
>> > code for Xen? 
> To cover for the vcpu1 -> vcpu2 -> vcpu1 case, i believe.

Ok, to cover it for non-synchronized TSC.  While KVM requires
synchronized TSC.

> > If that's the case, then it could be reverted indeed; but then why did
> > you commit this patch to 4.1? 
> 
> Because it fixes the problem Andy reported (see Subject: KVM: x86: fix
> kvmclock write race (v2) on kvm@). As long as you have Radim's
> fix on top.

But if it's so rare, and it was known that fixing the host protocol was
just as good a solution, why was the guest fix committed?

I'm just trying to understand.  I am worried that this patch was rushed
in; so far I had assumed it wasn't (a revert of a revert is rare enough
that you don't do it lightly...) but maybe I was wrong.

Right now I cannot even decide whether to revert it (and please Peter in
the process :)) or submit the Kconfig symbol patch officially.

Paolo
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