linux-kernel - Re: [PATCH v3 00/11] KVM: x86: track guest page access

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Message-ID: <56CC4CE2.1020209@redhat.com>
Date:	Tue, 23 Feb 2016 13:13:22 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	"Tian, Kevin" <kevin.tian@...el.com>,
	"Song, Jike" <jike.song@...el.com>,
	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
Cc:	"gleb@...nel.org" <gleb@...nel.org>,
	"mtosatti@...hat.com" <mtosatti@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kai.huang@...ux.intel.com" <kai.huang@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"Alex Williamson (alex.williamson@...hat.com)" 
	<alex.williamson@...hat.com>
Subject: Re: [PATCH v3 00/11] KVM: x86: track guest page access



On 23/02/2016 06:44, Tian, Kevin wrote:
>> From: Song, Jike
>> Sent: Tuesday, February 23, 2016 11:02 AM
>>
>> +Kevin
>>
>> On 02/22/2016 06:05 PM, Xiao Guangrong wrote:
>>>
>>> On 02/19/2016 08:00 PM, Paolo Bonzini wrote:
>>>>
>>>> I still have a doubt: how are you going to handle invalidation of GPU
>>>> shadow page tables if a device (emulated in QEMU or even vhost) does DMA
>>>> to the PPGTT?
>>>
>>> I think Jike is the better one to answer this question, Jike, could you
>>> please clarify it? :)
>>>
>>
>> Sure :)
>>
>> Actually in guest PPGTT is manipulated by CPU rather than GPU. The
>> PPGTT page table itself are plain memory, composed & modified by the
>> GPU driver, i.e. by CPU in Non-Root mode.
>>
>> Given that, we write-protected guest PPGTT, when VM writes PPGTT, EPT
>> violation rather than DMA fault happens.
> 
> 'DMA to PPGTT' is NOT SUPPORTED on our vGPU device model. Today
> Intel gfx driver doesn't use this method, and we explicitly list it as a
> guest driver requirement to support a vGPU. If a malicious driver does 
> program DMA to modify PPGTT, it can only modify guest PPGTT instead
> of shadow PPGTT (being guest invisible). So there is no security issue 
> either.

Ok, thanks for confirming.

Paolo