Re: [Qemu-devel] [PATCH v3 1/2] intel-iommu: differentiate host address width from IOVA address width.

[Michael S. Tsirkin]

On Sat, Dec 22, 2018 at 01:37:58AM +0800, Yu Zhang wrote:
> On Fri, Dec 21, 2018 at 12:04:49PM -0500, Michael S. Tsirkin wrote:
> > On Sat, Dec 22, 2018 at 12:09:44AM +0800, Yu Zhang wrote:
> > > Well, my understanding of the vt-d spec is that the address limitation in
> > > DMAR are referring to the same concept of CPUID.MAXPHYSADDR. I do not 
> > > think
> > > there's any different in the native scenario. :)
> > 
> > I think native machines exist on which the two values are different.
> > Is that true?
> 
> I think the answer is not. My understanding is that HAW(host address wdith) is
> the maximum physical address width a CPU can detects(by cpuid.0x80000008).
> 
> I agree there are some addresses the CPU does not touch, but they are still in
> the physical address space, and there's only one physical address space...
> 
> B.R.
> Yu

Ouch I thought we are talking about the virtual address size.
I think I did have a box where VTD's virtual address size was
smaller than CPU's.
For physical one - we just need to make it as big as max supported
memory right?

-- 
MST