Re: [RFC PATCH v3 1/2] x86: cpu/bugs: add AMD ERAPS support; hardware flushes RSB

[Dave Hansen]

On 11/28/24 05:28, Amit Shah wrote:
> From: Amit Shah <amit.shah@xxxxxxx>
> 
> When Automatic IBRS is disabled, Linux flushed the RSB on every context
> switch.  This RSB flush is not necessary in software with the ERAPS
> feature on Zen5+ CPUs that flushes the RSB in hardware on a context
> switch (triggered by mov-to-CR3).
> 
> Additionally, the ERAPS feature also tags host and guest addresses in
> the RSB - eliminating the need for software flushing of the RSB on
> VMEXIT.
> 
> Disable all RSB flushing by Linux when the CPU has ERAPS.
> 
> Feature mentioned in AMD PPR 57238.  Will be resubmitted once APM is
> public - which I'm told is imminent.

There was a _lot_ of discussion about this. But all of that discussion
seems to have been trimmed out and it seems like we're basically back
to: "this is new hardware supposed to mitigate SpectreRSB, thus it
mitigates SpectreRSB."

Could we please summarize the previous discussions in the changelog?
Otherwise, I fear it will be lost.