Re: [Xen-devel] [PATCH v2] xen/pvh: use a custom IO bitmap for PVH hardware domains

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 29/04/15 12:05, Roger Pau Monnà wrote:
> El 29/04/15 a les 2.38, Andrew Cooper ha escrit:
> > > +
> > > +    if ( is_pvh_domain(d) )
> > > +    {
> > > +        for ( i = 0; i < 0x10000; i++ )
> > > +            /* NB: 0xcf8 has special treatment so we need to trap it. */
> > Why?  (and irrespective of my question, cf8 expects a 4 byte access, and
> > surely cfc would need similar treatment?)
> 0xcfc-0xcff is already added to ioports_deny_access in construct_dom0. I
> have no idea why 0xcf8 needs this special treatment, but Linux PVH fails
> to enumerate PCI devices if Xen is not set to trap accesses to 0xcf8
> (FreeBSD seems to be fine, either with 0xcf8 trapped or not).
Sorry for the noise on v3.  I replied before seeing this reply.

cf8/cfc are used as an indirect pair for access to PCI config space.  
They must be strictly be controlled by a single entity in a system, or 
dom0 and Xen can race and interfere with each other.  As a result, 
permissions for cf8/cfc must never be set in the IO bitmap.
There are other indirect pairs which need similar treatment.  Please 
make sure that they get altered appropriately.  (see admin_io_ok(), 
which I think you can now fold given the updates to the dom0 io 
permission rangesets.)
~Andrew

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