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

[Jason Wang]

On 2017年01月23日 15:30, Peter Xu wrote:
> 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?
>
> Thanks,
>
> -- peterx

Yes, I misread the code, this is in fact triggered by guest.

Thanks