Re: [PATCH v3 0/4] x86/spec-ctrl: IPBP improvements

[Andrew Cooper <amc96@xxxxxxxx>]

On 25/01/2023 3:24 pm, Jan Beulich wrote:
> Versions of the two final patches were submitted standalone earlier
> on. The series here tries to carry out a suggestion from Andrew,
> which the two of us have been discussing. Then said previously posted
> patches are re-based on top, utilizing the new functionality.
>
> 1: spec-ctrl: add logic to issue IBPB on exit to guest
> 2: spec-ctrl: defer context-switch IBPB until guest entry
> 3: limit issuing of IBPB during context switch
> 4: PV: issue branch prediction barrier when switching 64-bit guest to kernel 
> mode

In the subject, you mean IBPB.  I think all the individual patches are fine.

Do you have an implementation of VMASST_TYPE_mode_switch_no_ibpb for
Linux yet?  The thing I'd like to avoid is that we commit this perf it
to Xen, without lining Linux up to be able to skip it.

~Andrew