linux-kernel - Re: [PATCH 0/2] KVM: MMU: support VMAs that got remap_pfn

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Date:	Tue, 5 Jul 2016 19:18:40 -0700
From:	Neo Jia <cjia@...dia.com>
To:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
CC:	Paolo Bonzini <pbonzini@...hat.com>,
	<linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
	Kirti Wankhede <kwankhede@...dia.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH 0/2] KVM: MMU: support VMAs that got remap_pfn_range-ed

On Wed, Jul 06, 2016 at 10:00:46AM +0800, Xiao Guangrong wrote:
> 
> 
> On 07/05/2016 08:18 PM, Paolo Bonzini wrote:
> >
> >
> >On 05/07/2016 07:41, Neo Jia wrote:
> >>On Thu, Jun 30, 2016 at 03:01:49PM +0200, Paolo Bonzini wrote:
> >>>The vGPU folks would like to trap the first access to a BAR by setting
> >>>vm_ops on the VMAs produced by mmap-ing a VFIO device.  The fault handler
> >>>then can use remap_pfn_range to place some non-reserved pages in the VMA.
> >>>
> >>>KVM lacks support for this kind of non-linear VM_PFNMAP mapping, and these
> >>>patches should fix this.
> >>
> >>Hi Paolo,
> >>
> >>I have tested your patches with the mediated passthru patchset that is being
> >>reviewed in KVM and QEMU mailing list.
> >>
> >>The fault handler gets called successfully and the previously mapped memory gets
> >>unmmaped correctly via unmap_mapping_range.
> >
> >Great, then I'll include them in 4.8.
> 
> Code is okay, but i still suspect if this implementation, fetch mmio pages in fault
> handler, is needed. We'd better include these patches after the design of vfio
> framework is decided.

Hi Guangrong,

I disagree. The design of VFIO framework has been actively discussed in the KVM
and QEMU mailing for a while and the fault handler is agreed upon to provide the
flexibility for different driver vendors' implementation. With that said, I am
still open to discuss with you and anybody else about this framework as the goal
is to allow multiple vendor to plugin into this framework to support their
mediated device virtualization scheme, such as Intel, IBM and us.

May I ask you what the exact issue you have with this interface for Intel to support 
your own GPU virtualization? 

Thanks,
Neo

>