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

[Jason Wang]

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?

Thanks

>   after the
> switch, we'll have D1 with both P1/P2 mapped, while domain B actually
> only has P2. That's unaligned mapping, and it should be wrong.
>
> If you (or anyone) think this is a bug as well for patch 18, I can
> just squash both 19/20 into patch 18.
>
> Thanks,
>
> -- peterx