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Re: [Qemu-devel] [PATCH RFC v4 19/20] intel_iommu: unmap existing pages

From: Peter Xu
Subject: Re: [Qemu-devel] [PATCH RFC v4 19/20] intel_iommu: unmap existing pages before replay
Date: Mon, 23 Jan 2017 15:30:20 +0800
User-agent: Mutt/1.5.24 (2015-08-30)

On Mon, Jan 23, 2017 at 09:57:23AM +0800, Jason Wang wrote:
> On 2017年01月22日 17:09, Peter Xu wrote:
> >On Sun, Jan 22, 2017 at 04:13:32PM +0800, Jason Wang wrote:
> >>
> >>On 2017年01月20日 21:08, Peter Xu wrote:
> >>>Previous replay works for domain switch only if the original domain does
> >>>not have mapped pages. For example, if we switch domain from A to B, it
> >>>will only work if A has no existing mapping. If there is, then there's
> >>>problem - current replay didn't make sure the old mappings are cleared
> >>>before replaying the new one.
> >>I'm not quite sure this is needed. I thought the only thing we need to do is
> >>stop DMA of device during the moving? Or is there an example that will cause
> >>trouble?
> >I think this patch is essential.
> >
> >Example:
> >
> >- device D1 moved to domain A, domain A has no mapping
> >- map page P1 in domain A, so D1 will have a mapping of page P1
> >- create domain B with mapping P2
> >- move D1 from domain A to domain B
> >
> >Here if we don't unmap existing pages in domain A (P1),
> I thought driver should do this work instead of device, because only driver
> knows whether or not iova is still needed?

Do you mean "device driver" above?

I don't know whether I understood the question above, but the problem
should be there no matter which one is managing iova?


-- peterx

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