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

Marcelo Tosatti
2015-04-22T22:57:09Z

On Wed, Apr 22, 2015 at 11:01:49PM +0200, Paolo Bonzini wrote:
>
>
> 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 don't know. Should have fixed the host protocol.

> 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.

Yes it was rushed in.

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