Re: [Qemu-devel] HPET configuration in Seabios

[Avi Kivity <avi@redhat.com>]

On 08/29/2011 01:14 AM, Kevin O'Connor wrote:
> On Sun, Aug 28, 2011 at 10:42:49PM +0200, Jan Kiszka wrote:
> >  On 2011-08-28 20:54, Alexander Graf wrote:
> >  >
> >  >  On 28.08.2011, at 02:42, Avi Kivity wrote:
> >  >
> >  >>  On 08/26/2011 08:32 AM, ya su wrote:
> >  >>>  hi,Avi:
> >  >>>
> >  >>>      I met the same problem, tons of hpet vm_exits(vector 209, fault
> >  >>>  address is in the guest vm's hpet mmio range), even I disable hpet
> >  >>>  device in win7 guest vm, it still produce a larget amount of vm_exits
> >  >>>  when trace-cmd ;  I add -no-hpet to start the vm, it still has HPET
> >  >>>  device inside VM.
> >  >>>
> >  >>>      Does that means the HPET device in VM does not depend on the
> >  >>>  emulated hpet device in qemu-kvm? Is there any way to disable the VM
> >  >>>  HPET device to prevent so many vm_exits?  Thansk.
> >  >>>
> >  >>
> >  >>  Looks like a bug to me.
> >  >
> >  >  IIRC disabling the HPET device doesn't remove the entry from the DSDT, no? So the guest OS might still think it's there while nothing responds (read returns -1).
> >
> >  Exactly. We have a fw_cfg interface in place for quite a while now
> >  (though I wonder how the firmware is supposed to tell -no-hpet apart
> >  from QEMU versions that don't provide this data - both return count =
> >  255), but SeaBios still exposes one HPET block at a hard-coded address
> >  unconditionally.
> >
> >  There was quite some discussion about the corresponding Seabios patches
> >  back then but apparently no consensus was found. Re-reading it, I think
> >  Kevin asked for passing the necessary DSDT fragments from QEMU to the
> >  firmware instead of using a new, proprietary fw_cfg format. Is that
> >  still the key requirement for any patch finally fixing this bug?
>
> My preference would be to use the existing ACPI table passing
> interface (fw_cfg slot 0x8000) to pass different ACPI tables to
> SeaBIOS.
>
> SeaBIOS doesn't currently allow that interface to override tables
> SeaBIOS builds itself, but it's a simple change to rectify that.
>
> When this was last proposed, it was raised that the header information
> in the ACPI table may then not match the tables that SeaBIOS builds.
> I think I proposed at that time that SeaBIOS could use the header of
> the first fw_cfg table (or some other fw_cfg interface) to populate
> the headers of its table headers.  However, there was no consensus.
>
> Note - the above is in regard to the HPET table.  If the HPET entry in
> the DSDT needs to be removed then that's a bigger change.
>

Can't seabios just poke at the hpet itself and see if it exists or not?

-- 
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