Re: [PATCH v2 0/8] x86/PV: avoid speculation abuse through guest accessors

[Jan Beulich <jbeulich@xxxxxxxx>]

On 19.02.2021 17:13, Ian Jackson wrote:
> Jan Beulich writes ("Re: [PATCH v2 0/8] x86/PV: avoid speculation abuse 
> through guest accessors"):
>> On 19.02.2021 16:50, Ian Jackson wrote:
>>> You say "consistency" but in practical terms, what will happen if the
>>> code is not "conxistent" in this sense ?
>>
>> Patches 4-6: The code is harder to understand with the mix of names.
>> Backports from future versions to 4.15 may require more attention to
>> get right (and then again the same level of attention when moving to
>> 4.14).
>>
>> Patches 7 is simply a minor improvement. Patch 8 is an equivalent
>> of the one patch of the earlier version which has already gone in.
>> Just like that other one it's more to avoid a latent issue than any
>> active one.
> 
> Thank you for this clear explanation.
> 
> I think 4-6 and 8 are good candidates for the reasons you give, and
> because they seem low risk to me.  Have you used any automatic
> techniques to check that there is no unintentional codegen change ?
> (Eg, binary diffs, diffing sedderied versions, or something.)

I did some manual inspection at the time of putting together that
work, but nothing further to be honest.

> To my naive eye patch 7 looks scary because it might be moving the
> scope of a critical section.  Am I wrong about that ?

At the source level it moves things, yes. Generated code, again as
per manual inspection, doesn't change, due to the pieces that the
compiler is able to eliminate. So I guess it's not as scary as it
may look.

Jan