Re: [patch V4 part 4 15/24] x86/db: Split out dr6/7 handling

[Alexandre Chartre]

On 5/5/20 3:49 PM, Thomas Gleixner wrote:
> From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>
> DR6/7 should be handled before nmi_enter() is invoked and restore after
> nmi_exit() to minimize the exposure.
>
> Split it out into helper inlines and bring it into the correct order.
>
> Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
>   arch/x86/kernel/hw_breakpoint.c |    6 ---
>   arch/x86/kernel/traps.c         |   62 +++++++++++++++++++++++++++-------------
>   2 files changed, 44 insertions(+), 24 deletions(-)
...
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -691,6 +691,44 @@ static bool is_sysenter_singlestep(struc
>   #endif
>   }
>   
> +static __always_inline void debug_enter(unsigned long *dr6, unsigned long *dr7)
> +{
> +	/*
> +	 * 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.
> +	 */
> +	get_debugreg(*dr7, 6);

Do you mean  get_debugreg(*dr7, 7); ?

alex.