Re: [PATCH 1/5] prctl: add PR_ISOLATE_BP process control

[Dominik Brodowski]

On Tue, Jan 23, 2018 at 02:07:01PM +0100, Martin Schwidefsky wrote:
> Add the PR_ISOLATE_BP operation to prctl. The effect of the process
> control is to make all branch prediction entries created by the execution
> of the user space code of this task not applicable to kernel code or the
> code of any other task.

What is the rationale for requiring a per-process *opt-in* for this added
protection?

For KPTI on x86, the exact opposite approach is being discussed (see, e.g.
http://lkml.kernel.org/r/1515612500-14505-1-git-send-email-w@xxxxxx ): By
default, play it safe, with KPTI enabled. But for "trusted" processes, one
may opt out using prctrl.

Thanks,
	Dominik