Re: [Qemu-devel] [PATCH] vfio: avoid adding same iommu mr for notify

[Peter Xu]

On Tue, Nov 15, 2016 at 04:11:57PM +1100, Alexey Kardashevskiy wrote:
> On 15/11/16 11:59, Peter Xu wrote:
> > When one IOMMU memory region is splitted into multiple memory sections,
> 
> 
> Out of curiosity - when does this happen?

My understanding: each PCI device will have one IOMMU region when with
vt-d vIOMMU enabled. After interrupt remapping is enabled, another
0xfeexxxxx region is overlapped to filter out the interrupts (see
vtd_find_add_as()). So the big Intel IOMMU region is splitted into
several.

Of course looks like we can remove the interrupt region and only use
one IOMMU region for both DMAR and IR, but I don't think that's a good
one, since maybe one day we'll have another scenario that will split a
single memory region. In that case, I'd prefer we take care of it
during registration.

Thanks,

-- peterx