On Mon, Dec 19, 2022 at 10:36:44PM -0800, Xin Li wrote:
> +static __always_inline void debug_kernel_common(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.
> - */
> - unsigned long dr7 = local_db_save();
> - irqentry_state_t irq_state = irqentry_nmi_enter(regs);
> instrumentation_begin();
>
> /*
> @@ -1062,7 +1050,8 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
> * Catch SYSENTER with TF set and clear DR_STEP. If this hit a
> * watchpoint at the same time then that will still be handled.
> */
> - if ((dr6 & DR_STEP) && is_sysenter_singlestep(regs))
> + if (!cpu_feature_enabled(X86_FEATURE_FRED) &&
> + (dr6 & DR_STEP) && is_sysenter_singlestep(regs))
> dr6 &= ~DR_STEP;
>
> /*
> @@ -1089,8 +1078,28 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
> regs->flags &= ~X86_EFLAGS_TF;
> out:
> instrumentation_end();
> - irqentry_nmi_exit(regs, irq_state);
> +}
Why doesn't the FRED handler get to to use irqentry_nmi_{enter,exit}() ?
> @@ -1179,6 +1188,24 @@ DEFINE_IDTENTRY_DEBUG_USER(exc_debug)
> {
> exc_debug_user(regs, debug_read_clear_dr6());
> }
> +
> +# ifdef CONFIG_X86_FRED
> +DEFINE_FRED_HANDLER(fred_exc_debug)
> +{
> + /*
> + * The FRED debug information saved onto stack differs from
> + * DR6 in both stickiness and polarity; it is exactly what
> + * debug_read_clear_dr6() returns.
> + */
> + unsigned long dr6 = fred_event_data(regs);
> +
> + if (user_mode(regs))
> + exc_debug_user(regs, dr6);
> + else
> + debug_kernel_common(regs, dr6);
> +}
> +# endif /* CONFIG_X86_FRED */
