* Gerd Hoffmann (kra...@redhat.com) wrote:
> > So that's mapped at an address beyond host phys-bits.
> > And it hasn't failed/crashed etc - but I guess maybe nothing is using that
> > 2G space?
>
> root@fedora ~# dmesg | grep Surface
> [ 4.830095] [drm] qxl: 2048M of Surface memory size
>
> qxl bar 4 (64bit) and qxl bar 1 (32bit) are the same thing. The 64bit
> bar can be alot larger obviously. The 32bit bar is just an alias for
> the first portion of the 64bit bar. So I guess qxl just falls back to
> use bar 1 instead of bar 4 because ioremap() on bar 4 fails.
>
> > Obviously 128T is a bit silly for maxmem at the moment, however I was
> > worrying what
> > happens with 36/39/40bit hosts, and it's not unusual to pick a maxmem
> > that's a few TB
> > even if the VMs you're initially creating are only a handful of GB.
> > (oVirt/RHEV seems to use
> > a 4TB default for maxmem).
>
> Oh, ok. Should be fixed I guess.
>
> > Still, this only hits as a problem if you hit the combination of:
> > a) You use large PCI bars
>
> ovmf will map all 64bit bars high, even without running out of 32bit
> address space. And with virtio 1.0 pretty much every virtual machine
> will have 64bit bars.
OK, yes I got that working, and you're right, it does map it high;
(with recent OVMF running virtio 1.0, that needed recent guest/host kernels)
and it does fail easily as well if memory doesn't fit, so for
example:
(all on a xeon with 46 bit physical host)
specifying maxmem=1T - upstream build is hanging - but works if I specify
phys-bits=46
so yes, it's noticing if the guest phys-bits is too small
even if the host can manage it.
It's OK if running with small amount of RAM and phys-bits=40
maxmem=64T with any phys-bits hangs.
specifying maxmem=64T with phys-bits=46 on xeon and it hangs
specifying maxmem=64T with phys-bits=48 on xeon and it hangs
specifying maxmem=32T with phys-bits=46-48 on xeon and it works
So for example we see:
Bus 2, device 4, function 0:
SCSI controller: PCI device 1af4:1042
IRQ 10.
BAR1: 32 bit memory at 0x98000000 [0x98000fff].
BAR4: 64 bit prefetchable memory at 0x200800000000 [0x2008007fffff].
id "virtio-disk0"
and that works nicely.
Dave
>
> cheers,
> Gerd
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
