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Re: [Qemu-devel] [RFC PATCH v3 3/3] VFIO Type1 IOMMU change: to support

From: Jike Song
Subject: Re: [Qemu-devel] [RFC PATCH v3 3/3] VFIO Type1 IOMMU change: to support with iommu and without iommu
Date: Mon, 16 May 2016 14:57:40 +0800
User-agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:17.0) Gecko/20130801 Thunderbird/17.0.8

On 05/13/2016 11:50 PM, Neo Jia wrote:
> On Fri, May 13, 2016 at 05:23:44PM +0800, Jike Song wrote:
>> On 05/13/2016 04:31 PM, Neo Jia wrote:
>>> On Fri, May 13, 2016 at 07:45:14AM +0000, Tian, Kevin wrote:
>>>> We use page tracking framework, which is newly added to KVM recently,
>>>> to mark RAM pages as read-only so write accesses are intercepted to 
>>>> device model.
>>> Yes, I am aware of that patchset from Guangrong. So far the interface are 
>>> all
>>> requiring struct *kvm, copied from https://lkml.org/lkml/2015/11/30/644
>>> - kvm_page_track_add_page(): add the page to the tracking pool after
>>>   that later specified access on that page will be tracked
>>> - kvm_page_track_remove_page(): remove the page from the tracking pool,
>>>   the specified access on the page is not tracked after the last user is
>>>   gone
>>> void kvm_page_track_add_page(struct kvm *kvm, gfn_t gfn,
>>>                 enum kvm_page_track_mode mode);
>>> void kvm_page_track_remove_page(struct kvm *kvm, gfn_t gfn,
>>>                enum kvm_page_track_mode mode);
>>> Really curious how you are going to have access to the struct kvm *kvm, or 
>>> you
>>> are relying on the userfaultfd to track the write faults only as part of the
>>> QEMU userfault thread?
>> Hi Neo,
>> For the vGPU used as a device for KVM guest, there will be interfaces
>> wrapped or implemented in KVM layer, as a rival thing diverted from
>> the interfaces for Xen. That is where the KVM related code supposed to be.
> Hi Jike,
> Is this discussed anywhere on the mailing list already? Sorry if I have missed
> such conversation.

Hi Neo,

Not exactly, but we can discuss it if necessary :)

Intel vGPU device-model, which is a part of i915 driver, has to be able to
emulate vGPU for *both* XenGT and KVMGT guests. That means there must be
a ridge somewhere, directing to Xen-specific and KVM-specific logic accordingly.


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