Re: [PATCH] x86/speculation: Avoid LFENCE in FILL_RETURN_BUFFER on CPUs that lack it

[Peter Zijlstra]

On Fri, Aug 19, 2022 at 02:33:08AM +0200, Ben Hutchings wrote:
> From: Ben Hutchings <benh@xxxxxxxxxx>
> 
> The mitigation for PBRSB includes adding LFENCE instructions to the
> RSB filling sequence.  However, RSB filling is done on some older CPUs
> that don't support the LFENCE instruction.
> 

Wait; what? There are chips that enable the RSB mitigations and DONT
have LFENCE ?!?