Re: [RFC PATCH V2 4/7] x86/hw_breakpoint: Prevent data breakpoints on user_pcid_flush_mask

[Lai Jiangshan]

On Tue, May 26, 2020 at 12:21 PM Andy Lutomirski <luto@xxxxxxxxxx> wrote:
>
> On Mon, May 25, 2020 at 6:42 PM Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx> wrote:
> >
> > The percpu user_pcid_flush_mask is used for CPU entry
> > If a data breakpoint on it, it will cause an unwanted #DB.
> > Protect the full cpu_tlbstate structure to be sure.
> >
> > There are some other percpu data used in CPU entry, but they are
> > either in already-protected cpu_tss_rw or are safe to trigger #DB
> > (espfix_waddr, espfix_stack).
>
> How hard would it be to rework this to have DECLARE_PERCPU_NODEBUG()
> and DEFINE_PERCPU_NODEBUG() or similar?


I don't know, but it is an excellent idea. Although the patchset
protects only 2 or 3 portions of percpu data, but there is many
percpu data used in tracing or kprobe code. They are needed to be
protected too.

Adds CC:
Steven Rostedt <rostedt@xxxxxxxxxxx>
Masami Hiramatsu <mhiramat@xxxxxxxxxx>