Re: [Patch v5 11/16] x86/speculation: Add Spectre v2 app to app protection modes

[Tim Chen]

On 11/19/2018 06:00 AM, Jiri Kosina wrote:
> On Mon, 19 Nov 2018, Thomas Gleixner wrote:
> 
>>> Yeah. IBPB implementation used to check the dumpability of tasks during 
>>> rescheduling, but that went away later.
>>>
>>> I still think that ideally that 'app2app' setting would toggle how IBPB is 
>>> being used as well, something along the lines:
>>>
>>> lite:
>>> 	- STIBP for the ones marked via prctl() and SECCOMP with the TIF_ 
>>> 	  flag
>>> 	- ibpb_needed() returning true for the same
>>>
>>> strict:
>>> 	- STIBP: as currently implemented
>>> 	- ibpb_needed() returning always true
>>>
>>> off:
>>> 	- neither STIBP nor IBPB applied ever
>>>
>>> That's give us also some % of performance lost via IBPB back.
>>>
>>> Makes sense?
>>
>> Except for the naming convention, yes. See other mail.
> 
> Actually Tim's patchset seems to already deal with IBPB in a consistent 
> way as well in
> 
> 	[11/16] x86/speculation: Add Spectre v2 app to app protection modes
> 
> but the fact that it's still using TIF_STIBP makes it a bit confusing and 
> hidden. So I'd suggest to fold something like below into it.
> 

Makes sense.  Will rename the flag.

Tim