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

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 08/02/12 17:05, Tim Deegan wrote:
> 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@citrix.com>
> 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.

Hmm - That is a very good point and I had not considered the
possibility.  I withdraw this patch pending more thought.

-- 
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com