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

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Date:	Mon, 18 Aug 2014 22:00:33 -0700
From:	David Matlack <dmatlack@...gle.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.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 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.

>> 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.
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