Re: [Xen-devel] [PATCH 0/4] x86: Drop PVRDTSCP and fix MSR_TSC_AUX handling for guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.11.18 at 18:43, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 16/11/2018 10:11, Jan Beulich wrote:
>>>>> On 15.11.18 at 22:47, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> Boris has confirmed that noone appears to be using PVRDTSCP any more, and in
>>> the decade since it was introduced, guest kernel / hardware support has
>>> provided a better alternative.
>> Doesn't removal of functionality require knowing that it was never used
>> at all, rather than just knowing that nothing uses it anymore? What if
>> some old guest somewhere relies on it?
> 
> Its an all-or-nothing feature.  The entirety of your VM userspace need
> to support it, or timing will go wrong on migrate.
> 
> We already established that it appears to be a vestigial Oracle-ism for
> which no consumer side code ever appeared, and that isn't used.
> 
> What is unacceptable is PVRDTSCP's implementation causing breakages in
> architectural behaviour for non-PVRDTSCP configurations, and one way or
> another, this needs fixing.
> 
> Please can we make a decision, because I don't have to time (or indeed,
> the want) to and fix this a 3rd different way if that's going to run
> into a similar reaction.

With Konrad's statement I'm fine with the removal. I'll get to look
at the individual patches.

Jan



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