On Wed, Sep 02, 2020 at 03:25:51PM +0200, Peter Zijlstra wrote:
> @@ -863,6 +849,18 @@ static void handle_debug(struct pt_regs
> static __always_inline void exc_debug_kernel(struct pt_regs *regs,
> unsigned long dr6)
> {
> + /*
> + * Disable breakpoints during exception handling; recursive exceptions
> + * are exceedingly 'fun'.
> + *
> + * Since this function is NOKPROBE, and that also applies to
> + * HW_BREAKPOINT_X, we can't hit a breakpoint before this (XXX except a
> + * HW_BREAKPOINT_W on our stack)
> + *
> + * Entry text is excluded for HW_BP_X and cpu_entry_area, which
> + * includes the entry stack is excluded for everything.
> + */
I know this comment was copy/pasted, but I had to stare at the last
paragraph like one of those 3D paintings they used to have at the mall.
Recommended rewording:
* HW_BREAKPOINT_X is disallowed for entry text; all breakpoints
* are disallowed for cpu_entry_area (which includes the entry
* stack).
--
Josh
