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Re: [PATCH for-4.17] x86/hvm: Revert per-domain APIC acceleration support
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- Date: Wed, 16 Nov 2022 18:14:46 +0000
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- Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Henry Wang <Henry.Wang@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 16 Nov 2022 18:15:07 +0000
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- Thread-topic: [PATCH for-4.17] x86/hvm: Revert per-domain APIC acceleration support
On 15/11/2022 08:49, Jan Beulich wrote:
> On 15.11.2022 01:35, Andrew Cooper wrote:
>> I was really hoping to avoid this, but its now too late in the 4.17 freeze
>> and
>> we still don't have working fixes.
>>
>> The in-Xen calculations for assistance capabilities are buggy. For the
>> avoidance of doubt, the original intention was to be able to control every
>> aspect of a APIC acceleration so we could comprehensively test Xen's support,
>> as it has proved to be buggy time and time again.
>>
>> Even after a protracted discussion on what the new API ought to mean,
>> attempts
>> to apply it to the existing logic have been unsuccessful, proving that the
>> API/ABI is too complicated for most people to reason about.
> Like Roger I'm still having trouble seeing what ABI you're talking
> about here. Yes, there are internal handling issues, but that's hardly
> "ABI". And as Roger indicated before, anything domctl/sysctl isn't
> stable anyway.
It absolutely is stable when it it extends beyond domctl/sysctl into the
libxl API, two different xl config files, and Xen command line (for PVH
dom0).
domctl/sysctl are the very least of the problem.
>> This reverts most of:
>> 2ce11ce249a3981bac50914c6a90f681ad7a4222
>> 6b2b9b3405092c3ad38d7342988a584b8efa674c
> plus (as per Fixes: tags)
>
> 399bcbf281bd936d1eff7f7d1054ab49115c3a44
> 0823d57d71c7023bea94d483f69f7b5e62820102
>
> which I think want mentioning here as well despite, like stated for the
> main commits, parts are left in place.
>
>> leaving in place the non-APIC specific changes (minimal as they are).
>>
>> This takes us back to the behaviour of Xen 4.16 where APIC acceleration is
>> configured on a per system basis.
>>
>> This work will be revisited in due course.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Provisional upon Roger not objecting (i.e. him at least remaining
> neutral), and preferably with the above remarks addressed:
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
Thanks.
~Andrew
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