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

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