linux-kernel - Re: [PATCH 1/2] KVM: X86: remove read buffer for mmio read

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Message-ID: <4FFC528D.8040900@redhat.com>
Date:	Tue, 10 Jul 2012 19:04:29 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 1/2] KVM: X86: remove read buffer for mmio read

On 07/10/2012 04:01 PM, Gleb Natapov wrote:
> On Tue, Jul 10, 2012 at 03:50:39PM +0300, Avi Kivity wrote:
> > On 07/10/2012 01:48 PM, Gleb Natapov wrote:
> > > > > > 
> > > > > But the code is already here, why drop it?
> > > > 
> > > > The read cache is not effective for multiple disjunct reads.
> > > What do you mean?
> > 
> > If an instruction reads from several sources in mmio, then the first
> > read will be flushed from the cache by the second read.  So if we need a
> > third read, we'll have to exit for the first again.
> > 
> The cache is flashed only before instruction decode, never during
> emulation.

Oh, I misread the code.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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