Re: [Qemu-devel] [PATCH RFC] memory: drop _overlap variant

[Michael S. Tsirkin]

On Tue, Feb 19, 2013 at 05:58:38PM +0200, Avi Kivity wrote:
> On Tue, Feb 19, 2013 at 4:41 PM, Michael S. Tsirkin <address@hidden> wrote:
> > On Thu, Feb 14, 2013 at 08:23:04PM +0200, Avi Kivity wrote:
> >> On Thu, Feb 14, 2013 at 8:12 PM, Michael S. Tsirkin <address@hidden> wrote:
> >> >>
> >> >> Is there an actual real problem that needs fixing?
> >> >
> >> > Yes. Guests sometimes cause device BARs to temporary overlap
> >> > the APIC range during BAR sizing. It works fine on a physical
> >> > system but fails on KVM since pci has same priority.
> >> >
> >> > See the report:
> >> > [BUG] Guest OS hangs on boot when 64bit BAR present
> >> >
> >>
> >> Is PCI_COMMAND_MEMORY set while this is going on?
> >
> > I think Linux never clears PCI_COMMAND_MEMORY because
> > it's buggy in some devices.
> 
> Ok.  Then I recommend defining the MSI message area as overlapped with
> sufficient priority.  It should probably be a child of the PCI address
> space.
> 
> The IOAPIC is actually closer to ISA, but again it's sufficient to
> move it to the PCI address space.  I doubt its priority matters.

Well moving IOAPIC to PCI seems strange, it's not a PCI thing,
and I think it can be moved outside PCI though guests don't do it.
So I think ideally we really should have it look something like:

        sysbus -> ioapic
               -> pci -> msi

-- 
MST