Re: [Qemu-devel] [PATCH RFC v3 02/14] intel_iommu: simplify irq region translation

[Peter Xu <peterx@redhat.com>]

On Fri, Jan 20, 2017 at 09:52:01AM +0000, Tian, Kevin wrote:

[...]

> btw what about guest setups a valid mapping at 0xFEEx_xxxx in
> its remapping structure, which is then programmed to virtual
> device as DMA destination? Then when emulating that virtual DMA,
> vtd_do_iommu_translate should simply return (maybe throw out
> a warning for diagnostic purpose) instead of assert here. 
> 
> VT-d spec defines as below:
> 
> 	Software must ensure the second-level paging-structure entries 
> 	are programmed not to remap input addresses to the interrupt 
> 	address range. Hardware behavior is undefined for memory 
> 	requests remapped to the interrupt address range.

Thanks for this reference. That's something I was curious about.

> 
> I don't think "hardware behavior is undefined" is equal to "assert
> thus kill VM"...

I don't think it will kill the VM. After we have the MSI region, it
should just use that IR region for everything (read/write/translate).
So iiuc when anyone setups IOVA mapping within range 0xfeexxxxx, then
a DMA will trigger an interrupt (rather than memory moves), but in
most cases the interrupt will be illegal since either the data is
invalid (e.g., non-zero reserved bits, or SID verification failure),
further it should trigger a vIOMMU fault (though IR fault reporting is
still incomplete, that's my next thing to do after this series).

Thanks,

-- peterx