Re: [Xen-devel] [PATCH 3 of 4] VIOAPIC: Emulate a version 0x20 IOAPIC

[Tim Deegan <tim@xxxxxxx>]

At 16:45 +0000 on 08 Feb (1328719538), Andrew Cooper wrote:
> Currently, hvm emulates a version 0x11 IOAPIC.  However, depending on
> the HVM guests {IO,L}APIC setup, it may take fewer traps into Xen by
> directly using the VIOAPIC EOI register present in version 0x20,
> rather than resorting to the legacy method of flipping the trigger
> mode for the relevent RTE.
> 
> Currently, all required functionality is already present in the code,
> except that it is covered by VIOAPIC_IS_IOSAPIC which is never defined.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

This probably ought to introduce a hvm save record to say which kind of
IOAPIC the VM was booted with, so that after a live migration the OS
doesn't get confused. :(

It seems unlikely that any OSes rely on the IOAPIC version (and the
behaviour of that register) being static after boot, but better safe
than sorry - there might be some confusion in resume from S3 or similar.

Tim.


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