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

[Avi Kivity]

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.