Re: [PATCH 3/3] x86/entry: Use PUSH_AND_CLEAR_GPRS and drop SAVE_ALL

[Jan Beulich <jbeulich@xxxxxxxx>]

On 07.07.2026 18:09, Andrew Cooper wrote:
> On 07/07/2026 8:16 am, Jan Beulich wrote:
>> Btw, as it occurs to me while mentioning SLS: Judging from the patches I
>> have, IRET looks to be immune, albeit I can't find any statement in the doc.
>> What about ERET{S,U}, uses of which we've gained only relatively recently?
> I think the bit you want is in SDM Vol2.  For ERETS:
> 
> "Instruction ordering. Instructions following execution of ERETS may be
> fetched from memory before earlier instructions complete execution, but
> they will not execute (even speculatively) until all instructions prior
> to ERETS have completed execution (the later instructions may execute
> before data stored by the earlier instructions have become globally
> visible)."
> 
> and says the same for ERETU.  Sadly, "following" is ambiguous in the
> context of SLS, but an ERETS-to-self could end up legitimately executing
> the next sequential instruction.  Either way, the "not execute even
> speculatively" is the property wanted.

There's a worse ambiguity here, imo: What they say excludes ERETS itself.
I.e. while ERETS itself executes, subsequent instruction may already be
speculated.

Interestingly the FRED spec (9.0) says such only for ERETU, not ERETS.

Jan