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

[Peter Xu <peterx@redhat.com>]

On Sun, Jan 22, 2017 at 04:42:13AM +0000, Tian, Kevin wrote:
> > From: Peter Xu [mailto:peterx@redhat.com]
> > Sent: Friday, January 20, 2017 6:04 PM
> > 
> > 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).
> > 
> 
> Yes, you're right here. Sorry for bothering with my wrong understanding. :-)

No problem at all.

Looking forward to any of your further comments on v4. :-)

-- peterx