Messages in this thread | | | From | "Van De Ven, Arjan" <> | Subject | RE: [patch RFC 5/5] x86/speculation: Add basic speculation control code | Date | Wed, 10 Jan 2018 13:51:31 +0000 |
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> So here is the simple list of questions all to be answered with YES or > NO. I don't want to see any of the 'but, though ...'. We all know by now > that it's CPU dependent and slow and whatever and that IBRS_ATT will be in > future CPUs. So get your act together and tell a clear YES or NO.
I will answer for current cpus, so those not having IBRS_ATT > > 1) Does IBRS=1 when set once act as a set-and-forget option ?
NO
> 1a) If the answer to #1 is yes, is it more secure than toggling it?
NO > > 1b) If the answer to #1 is yes, is retpoline required ?
NO - Once you have IBRS done PROPERLY (toggled) you don't need retpoline > > 1c) If the answer to #1 is yes, is RSB stuffing required ?
Only for the VM exit case
> > 2) Does toggle mode of IBRS require retpoline ?
NO
> > 3) Does toggle mode of IBRS require RSB stuffing ?
Only for the VM exit case > > 4) Exist CPUs which require IBRS to be selected automatically ?
I do not understand your question exactly
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