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

From: Paolo Bonzini <pbonzini@redhat.com>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	torvalds@linux-foundation.org, linux-kernel@vger.kernel.org,
	gleb@kernel.org, kvm@vger.kernel.org,
	Ralf Baechle <ralf@linux-mips.org>,
	luto@kernel.org
Subject: Re: [GIT PULL] First batch of KVM changes for 4.1
Date: Thu, 23 Apr 2015 13:29:28 +0200	[thread overview]
Message-ID: <5538D798.1090509@redhat.com> (raw)
In-Reply-To: <20150422225559.GA21667@amt.cnet>

On 23/04/2015 00:55, Marcelo Tosatti wrote:
> 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.

No problem.  Let's do the right thing now.

>> 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.

Ok, so re-reverted it will be.

Paolo