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

[Thomas Gleixner]

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.

Thanks,

        tglx