Re: [PATCH v2 4/8] x86/spec_ctrl: Add sysctl knobs to enable/disable SPEC_CTRL feature

[Dave Hansen]

On 01/06/2018 06:41 AM, Konrad Rzeszutek Wilk wrote:
>>  .macro DISABLE_IBRS
>> -	ALTERNATIVE "jmp .Lskip_\@", "", X86_FEATURE_SPEC_CTRL
>> +	testl	$1, dynamic_ibrs
> On every system call we end up hammering on this 'dynamic_ibrs'
> variable. And it looks like it can be flipped via the IPI mechanism.
> 
> Would it make sense for this to be per-cpu?

It's probably better to either just make it __read_mostly or get the
static branches that folks were suggesting actually working.