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

[Michael S. Tsirkin]

On Thu, Feb 14, 2013 at 05:07:02PM +0200, Avi Kivity wrote:
> On Thu, Feb 14, 2013 at 4:40 PM, Michael S. Tsirkin <address@hidden> wrote:
> > On Thu, Feb 14, 2013 at 04:14:39PM +0200, Avi Kivity wrote:
> >
> > But some parents are system created and shared by many devices so children 
> > for
> > such have no idea who their siblings are.
> >
> > Please take a look at the typical map in this mail:
> > '[BUG] Guest OS hangs on boot when 64bit BAR present'
> >
> > system overlap 0 pri 0 [0x0 - 0x7fffffffffffffff]
> >      kvmvapic-rom overlap 1 pri 1000 [0xca000 - 0xcd000]
> >          pc.ram overlap 0 pri 0 [0xca000 - 0xcd000]
> >          ++ pc.ram [0xca000 - 0xcd000] is added to view
> >      ....................
> >      smram-region overlap 1 pri 1 [0xa0000 - 0xc0000]
> >          pci overlap 0 pri 0 [0xa0000 - 0xc0000]
> >              cirrus-lowmem-container overlap 1 pri 1 [0xa0000 - 0xc0000]
> >                  cirrus-low-memory overlap 0 pri 0 [0xa0000 - 0xc0000]
> >                 ++cirrus-low-memory [0xa0000 - 0xc0000] is added to view
> >      kvm-ioapic overlap 0 pri 0 [0xfec00000 - 0xfec01000]
> >     ++kvm-ioapic [0xfec00000 - 0xfec01000] is added to view
> >      pci-hole64 overlap 0 pri 0 [0x100000000 - 0x4000000100000000]
> >          pci overlap 0 pri 0 [0x100000000 - 0x4000000100000000]
> >      pci-hole overlap 0 pri 0 [0x7d000000 - 0x100000000]
> >          pci overlap 0 pri 0 [0x7d000000 - 0x100000000]
> >              ivshmem-bar2-container overlap 1 pri 1 [0xfe000000 - 
> > 0x100000000]
> >                  ivshmem.bar2 overlap 0 pri 0 [0xfe000000 - 0x100000000]
> >                 ++ivshmem.bar2 [0xfe000000 - 0xfec00000] is added to view
> >                 ++ivshmem.bar2  [0xfec01000 - 0x100000000] is added to view
> >
> > As you see, ioapic at 0xfec00000 overlaps pci-hole.
> > ioapic is guest programmable in theory - should use _overlap?
> > pci-hole is not but can overlap with ioapic.
> > So also _overlap?
> 
> It's a bug.  The ioapic is in the pci address space, not the system
> address space.  And yes it's overlappable.

So you want to put it where? Under pci-hole?
And we'll have to teach all machine types
creating pci-hole about it?

> >
> > Let's imagine someone writes a guest programmable device for
> > ARM. Now we should update all ARM devices from regular to _overlap?
> 
> It's sufficient to update the programmable device.

Then the device can be higher priority (works for apic)
but not lower priority. Make priority signed?

> >> >
> >> > Non overlapping is not a common case at all.  E.g. with normal PCI
> >> > devices you have no way to know nothing overlaps - addresses are guest
> >> > programmable.
> >>
> >> Non overlapping is mostly useful for embedded platforms.
> >
> > Maybe it should have a longer name like _nonoverlap then?
> > Current API makes people assume _overlap is only for special
> > cases and default should be non overlap.
> 
> The assumption is correct.