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

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Date:	Mon, 9 Jul 2012 16:26:42 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Avi Kivity <avi@...hat.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 Mon, Jul 09, 2012 at 09:23:03PM +0800, Xiao Guangrong wrote:
> On 07/09/2012 08:49 PM, Avi Kivity wrote:
> > On 07/09/2012 02:23 PM, Gleb Natapov wrote:
> >>
> >>> kvm-unit-tests.git has a test for xchg to mmio.  Does it still work?
> >>>
> >>> I agree this code has to go, but it needs to be replaced by something.
> >>> Maybe a .valid flag in struct operand.
> >>>
> >> Valid will not enough for that.
> > 
> > If we make everything go through operands, any reason why not?
> > 
> 
> I noticed some instructions need to read ESP for many times (e.g, iret_real),
> maybe .valid flag is not enough for this case if the stack is in MMIO, yes?
> 
> IIUC, I also noticed ESP is not reset back if it is emulated fail (mmio is needed).
> If the stack located in mmio region, this kind of instruct will be broken, i know no
> guest will use mmio as stack but SDM does not limit it, is it valid?
> 
Good point about MMIO stack too.

--
			Gleb.
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