Re: [PATCH 1/2] x86/hw_breakpoint: Prevent data breakpoints on __per_cpu_offset

[Peter Zijlstra]

On Fri, Feb 05, 2021 at 12:45:54PM +0100, Thomas Gleixner wrote:
> On Thu, Feb 04 2021 at 16:11, Andy Lutomirski wrote:
> > On Thu, Feb 4, 2021 at 6:26 AM Lai Jiangshan <jiangshanlai@xxxxxxxxx> wrote:
> >> When FSGSBASE is enabled, paranoid_entry() fetches the per-CPU
> >> GSBASE value via __per_cpu_offset or pcpu_unit_offsets.
> >>
> >> When data breakpoint is set on __per_cpu_offset[cpu] (read-write
> >> operation), the specific cpu will be stuck in the infinite #DB loop.
> >> RCU will try to send NMI to the specific cpu, but it is not working
> >> either since NMI also relies on paranoid_entry().
> >
> > Should we consider having a .percpu..noinstr section and having
> > objtool enforce this?
> 
> I think so.

I'll put it on the TODO list somewhere ...