Re: [PATCH] VT-d: Fix iommu map page for mmio pages

[Muli Ben-Yehuda <muli@il.ibm.com>]

On Thu, Sep 25, 2008 at 05:45:30PM +0300, Avi Kivity wrote:
> Han, Weidong wrote:
>> Is it possible DMA into an mmio page? 
>
> I don't see why not.

Two reasons. First it makes no sense. MMIO pages don't have RAM
backing them, they have another device's register window. So the
effect of DMA'ing into an MMIO page would be for one device to DMA
into the register window of another device, which sounds to me insane.

Second, and more importantly, I've seen systems where doing the above
caused a nice, immediate, reboot. So I think that unless someone comes
with a valid scenario where we need to support it or something breaks,
we'd better err on the side of caution and not map pages that should
not be DMA targets.

Cheers,
Muli
-- 
The First Workshop on I/O Virtualization (WIOV '08)
Dec 2008, San Diego, CA, http://www.usenix.org/wiov08/
                      xxx
SYSTOR 2009---The Israeli Experimental Systems Conference
http://www.haifa.il.ibm.com/conferences/systor2009/