Re: [PATCH 02/13] x86/debug: Allow a single level of #DB recursion

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).