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Re: [Xen-devel] [PATCH v2] x86/AMD: unbreak CPU hotplug on AMD systems without RstrFpErrPtrs

On 10.12.2019 13:37, Andrew Cooper wrote:
> On 10/12/2019 10:26, Jürgen Groß wrote:
>> On 10.12.19 11:10, Jan Beulich wrote:
>>> On 04.12.2019 00:56, Igor Druzhinin wrote:
>>>> If the feature is not present Xen will try to force X86_BUG_FPU_PTRS
>>>> feature at CPU identification time. This is especially noticeable in
>>>> PV-shim that usually hotplugs its vCPUs. We either need to restrict
>>>> this
>>>> action for boot CPU only or allow secondary CPUs to modify
>>>> forced CPU capabilities at runtime. Choose the former since modifying
>>>> forced capabilities out of boot path leaves the system in potentially
>>>> inconsistent state.
>>>> Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
>>> I've committed this to unstable, as per the outcome of the
>>> community call.
> What outcome?  Yes technically your R-by is sufficient to get the patch
> in, but you know very well there are open objections against this
> version of the patch.

My proposal on the call was to go with the existing patch, and improve
from there. There wasn't great enthusiasm, but there was agreement that
this is the most pragmatic route to follow. In particular I don't
recall you voicing any objection to this on the call (I do very well
recall the objection you voiced earlier on, which I had responded to
with a suggestion of a slightly different approach, taking care [I
think] of your wishes as well as mine).

> Also, you're actually in a position where you are reviewing your own
> work, which is not how R-by is intended to work.

Which own work? The patch doesn't even carry a Suggested-by. Iirc
Igor told me that what has gone in is how he had it initially. So
I'm pretty confused by this statement of yours.

Furthermore, as a recurring pattern, simply not responding to ongoing
discussions should not, in the common case, lead to no progress at
all. Iirc this was also mentioned on the call ("lazy consensus").

> Furthermore, you will observe that there is an action item on me from
> the call to come up with a less broken alternative which I'm genuinely
> attempting to do.

There's no indication towards this in the minutes, afaics. Or wait
- the same topic appears twice there (as both 4 and 6). I wasn't
even aware of such an action item. I'll be happy to revert if you
indicate so, and if a better fix is going to show up in time.


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