Re: [Qemu-devel] [PATCH 4/7] kvm: Add sanity checks to slot management

[Hollis Blanchard]

On Wed, 2009-04-29 at 12:38 -0500, Anthony Liguori wrote:
> Hollis Blanchard wrote:
> > On Wed, 2009-04-29 at 12:38 +0200, Jan Kiszka wrote:
> >   
> >> What is the alignment of those regions then? None? And do regions of
> >> different types overlap even on the same page? Maybe the check reveals
> >> some deeper conflict /wrt KVM. Can you point me to the involved code files?
> >>     
> >
> > These PCI controllers make separate calls to
> > cpu_register_physical_memory() for separate callbacks. Reading
> > ppce500_pci_init(), for example:
> > 0xe0008000 -> CFGADDR (4 bytes)
> > 0xe0008004 -> CFGDATA (4 bytes)
> > 0xe0008c00 -> other registers
> >   
> 
> That's goofy.  If the single device owns the entire region, it should 
> region the entire region instead of relying on subpage functionality.
> 
> If just requires a switch() on the address to dispatch to the 
> appropriate functions.  It should be easy enough to fix.

There are two cases that share this code path:
1) same driver registers multiple regions in the same page
2) different drivers register regions in the same page

This is case 1, and as you say, we could add a switch statement to
handle it. I did not look closely to see how many other callers fall
into this category.

However, are you suggesting that case 2 is also "goofy" and will never
work with KVM? It works in qemu today. As long as case 2 works, case 1
will work too, so why change anything?

-- 
Hollis Blanchard
IBM Linux Technology Center