linux-kernel - Re: [PATCH 1/2] KVM: fix cache stale memslot info with correct mmio generation number

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Message-ID: <53F2DE4B.4060708@linux.vnet.ibm.com>
Date:	Tue, 19 Aug 2014 13:19:07 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	David Matlack <dmatlack@...gle.com>
CC:	Paolo Bonzini <pbonzini@...hat.com>,
	Gleb Natapov <gleb@...nel.org>,
	Avi Kivity <avi.kivity@...il.com>, mtosatti@...hat.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH 1/2] KVM: fix cache stale memslot info with correct mmio
 generation number

On 08/19/2014 01:00 PM, David Matlack wrote:
> On Mon, Aug 18, 2014 at 9:41 PM, Xiao Guangrong
> <xiaoguangrong@...ux.vnet.ibm.com> wrote:
>> On 08/19/2014 12:31 PM, David Matlack wrote:
>>> But it looks like you basically said the same thing earlier, so I think
>>> we're on the same page.
>>>
>>
>> Yes, that is what i try to explain in previous mails. :(
> 
> I'm glad we understand each other now! Sorry again for my confusion.

Yup, me too. :)

> 
>>> The single line patch I suggested was only intended to fix the "forever
>>> incorrectly exit mmio".
>>
>> My patch also fixes this case and that does not doubly increase the
>> number. I think this is the better one.
> 
> I prefer doubly increasing the generation for this reason: the updated boolean
> requires extra code on the "client-side" to check if there's an update in
> progress. And that makes it easy to get wrong. In fact, your patch
> forgot to check the updated bit in mark_mmio_spte(). Doubly increasing the
> generation requires no "client-side" code to work.

No, the updated patch is used to fix case 2 which i draw the scenario in
the last mail. I mean the original patch in this patchset which just
increase the number after srcu-sync.

Then could you tell me that your approach can do but my original patch can not?

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