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

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Message-ID: <4FFADB37.4090705@linux.vnet.ibm.com>
Date:	Mon, 09 Jul 2012 21:23:03 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Gleb Natapov <gleb@...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 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?




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