Re: [PATCH 23/35] x86/speculation: Add basic speculation control code

[Dave Hansen]

On 01/18/2018 08:37 AM, Josh Poimboeuf wrote:
>>
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -3932,6 +3932,7 @@
>>  			retpoline	  - replace indirect branches
>>  			retpoline,generic - google's original retpoline
>>  			retpoline,amd     - AMD-specific minimal thunk
>> +			ibrs		  - Intel: Indirect Branch Restricted Speculation
> Are there plans to add spectre_v2=ibrs_always to prevent SMT-based
> attacks?

What does "ibrs_always" mean to you?

There is a second bit in the MSR (STIBP) that is intended to keep
hyperthreads from influencing each-other.  That is behavior is implicit
when IBRS is enabled.

I think ibrs_always *should* probably be kept to refer to the future
CPUs that can safely leave IBRS enabled all the time.