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

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Message-ID: <4eb9131a-d2cb-9142-1db3-d7138bf03309@redhat.com>
Date:	Wed, 6 Jul 2016 08:05:15 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>,
	Neo Jia <cjia@...dia.com>
Cc:	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 06/07/2016 04:00, 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.

I think that this fixes a bug anyway, the previous handling of VM_PFNMAP
is too simplistic.

Paolo