Re: [PATCH v2 09/16] powerpc/watchpoint: Convert thread_struct->hw_brk to an array

[Christophe Leroy <christophe.leroy@c-s.fr>]

Le 01/04/2020 à 08:13, Ravi Bangoria a écrit :
> So far powerpc hw supported only one watchpoint. But Future Power
> architecture is introducing 2nd DAWR. Convert thread_struct->hw_brk
> into an array.
> 
> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
> ---
>   arch/powerpc/include/asm/processor.h      |  2 +-
>   arch/powerpc/kernel/process.c             | 61 ++++++++++++++---------
>   arch/powerpc/kernel/ptrace/ptrace-noadv.c | 40 +++++++++++----
>   arch/powerpc/kernel/ptrace/ptrace32.c     |  4 +-
>   arch/powerpc/kernel/signal.c              |  9 +++-
>   5 files changed, 77 insertions(+), 39 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
> index 90f6dbc7ff00..65b03162cd67 100644
> --- a/arch/powerpc/include/asm/processor.h
> +++ b/arch/powerpc/include/asm/processor.h
> @@ -187,7 +187,7 @@ struct thread_struct {
>   	 */
>   	struct perf_event *last_hit_ubp;
>   #endif /* CONFIG_HAVE_HW_BREAKPOINT */
> -	struct arch_hw_breakpoint hw_brk; /* info on the hardware breakpoint */
> +	struct arch_hw_breakpoint hw_brk[HBP_NUM_MAX]; /* hardware breakpoint info */
>   	unsigned long	trap_nr;	/* last trap # on this thread */
>   	u8 load_slb;			/* Ages out SLB preload cache entries */
>   	u8 load_fp;
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index e0275fcd0c55..f5b4f21e822b 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -704,21 +704,50 @@ void switch_booke_debug_regs(struct debug_reg *new_debug)
>   EXPORT_SYMBOL_GPL(switch_booke_debug_regs);
>   #else	/* !CONFIG_PPC_ADV_DEBUG_REGS */
>   #ifndef CONFIG_HAVE_HW_BREAKPOINT
> -static void set_breakpoint(struct arch_hw_breakpoint *brk)
> +static void set_breakpoint(struct arch_hw_breakpoint *brk, int i)
>   {
>   	preempt_disable();
> -	__set_breakpoint(brk, 0);
> +	__set_breakpoint(brk, i);
>   	preempt_enable();
>   }
>   
>   static void set_debug_reg_defaults(struct thread_struct *thread)
>   {
> -	thread->hw_brk.address = 0;
> -	thread->hw_brk.type = 0;
> -	thread->hw_brk.len = 0;
> -	thread->hw_brk.hw_len = 0;
> -	if (ppc_breakpoint_available())
> -		set_breakpoint(&thread->hw_brk);
> +	int i;
> +
> +	for (i = 0; i < nr_wp_slots(); i++) {

Maybe you could add the following that you added other places:

	struct arch_hw_breakpoint null_brk = {0};

Then do

	thread->hw_brk[i] = null_brk;

> +		thread->hw_brk[i].address = 0;
> +		thread->hw_brk[i].type = 0;
> +		thread->hw_brk[i].len = 0;
> +		thread->hw_brk[i].hw_len = 0;
> +		if (ppc_breakpoint_available())
> +			set_breakpoint(&thread->hw_brk[i], i);
> +	}
> +}
> +
> +static inline bool hw_brk_match(struct arch_hw_breakpoint *a,
> +				struct arch_hw_breakpoint *b)
> +{
> +	if (a->address != b->address)
> +		return false;
> +	if (a->type != b->type)
> +		return false;
> +	if (a->len != b->len)
> +		return false;
> +	/* no need to check hw_len. it's calculated from address and len */
> +	return true;
> +}
> +
> +static void switch_hw_breakpoint(struct task_struct *new)
> +{
> +	int i;
> +
> +	for (i = 0; i < nr_wp_slots(); i++) {
> +		if (unlikely(!hw_brk_match(this_cpu_ptr(&current_brk[i]),
> +					   &new->thread.hw_brk[i]))) {
> +			__set_breakpoint(&new->thread.hw_brk[i], i);
> +		}

Or could be:

		if (likely(hw_brk_match(this_cpu_ptr(&current_brk[i]),
					&new->thread.hw_brk[i])))
			continue;
		__set_breakpoint(&new->thread.hw_brk[i], i);


> +	}
>   }
>   #endif /* !CONFIG_HAVE_HW_BREAKPOINT */
>   #endif	/* CONFIG_PPC_ADV_DEBUG_REGS */
> @@ -822,19 +851,6 @@ bool ppc_breakpoint_available(void)
>   }
>   EXPORT_SYMBOL_GPL(ppc_breakpoint_available);
>   
> -static inline bool hw_brk_match(struct arch_hw_breakpoint *a,
> -			      struct arch_hw_breakpoint *b)
> -{
> -	if (a->address != b->address)
> -		return false;
> -	if (a->type != b->type)
> -		return false;
> -	if (a->len != b->len)
> -		return false;
> -	/* no need to check hw_len. it's calculated from address and len */
> -	return true;
> -}
> -
>   #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
>   
>   static inline bool tm_enabled(struct task_struct *tsk)
> @@ -1167,8 +1183,7 @@ struct task_struct *__switch_to(struct task_struct *prev,
>    * schedule DABR
>    */
>   #ifndef CONFIG_HAVE_HW_BREAKPOINT
> -	if (unlikely(!hw_brk_match(this_cpu_ptr(&current_brk[0]), &new->thread.hw_brk)))
> -		__set_breakpoint(&new->thread.hw_brk, 0);
> +	switch_hw_breakpoint(new);
>   #endif /* CONFIG_HAVE_HW_BREAKPOINT */
>   #endif
>   
> diff --git a/arch/powerpc/kernel/ptrace/ptrace-noadv.c b/arch/powerpc/kernel/ptrace/ptrace-noadv.c
> index 12962302d6a4..0dbb35392dd2 100644
> --- a/arch/powerpc/kernel/ptrace/ptrace-noadv.c
> +++ b/arch/powerpc/kernel/ptrace/ptrace-noadv.c
> @@ -67,11 +67,16 @@ int ptrace_get_debugreg(struct task_struct *child, unsigned long addr,
>   	/* We only support one DABR and no IABRS at the moment */
>   	if (addr > 0)
>   		return -EINVAL;
> -	dabr_fake = ((child->thread.hw_brk.address & (~HW_BRK_TYPE_DABR)) |
> -		     (child->thread.hw_brk.type & HW_BRK_TYPE_DABR));
> +	dabr_fake = ((child->thread.hw_brk[0].address & (~HW_BRK_TYPE_DABR)) |
> +		     (child->thread.hw_brk[0].type & HW_BRK_TYPE_DABR));
>   	return put_user(dabr_fake, datalp);
>   }
>   
> +/*
> + * ptrace_set_debugreg() fakes DABR and DABR is only one. So even if
> + * internal hw supports more than one watchpoint, we support only one
> + * watchpoint with this interface.
> + */
>   int ptrace_set_debugreg(struct task_struct *task, unsigned long addr, unsigned long data)
>   {
>   #ifdef CONFIG_HAVE_HW_BREAKPOINT
> @@ -137,7 +142,7 @@ int ptrace_set_debugreg(struct task_struct *task, unsigned long addr, unsigned l
>   			return ret;
>   
>   		thread->ptrace_bps[0] = bp;
> -		thread->hw_brk = hw_brk;
> +		thread->hw_brk[0] = hw_brk;
>   		return 0;
>   	}
>   
> @@ -159,12 +164,24 @@ int ptrace_set_debugreg(struct task_struct *task, unsigned long addr, unsigned l
>   	if (set_bp && (!ppc_breakpoint_available()))
>   		return -ENODEV;
>   #endif /* CONFIG_HAVE_HW_BREAKPOINT */
> -	task->thread.hw_brk = hw_brk;
> +	task->thread.hw_brk[0] = hw_brk;
>   	return 0;
>   }
>   
> +static int find_empty_hw_brk(struct thread_struct *thread)
> +{
> +	int i;
> +
> +	for (i = 0; i < nr_wp_slots(); i++) {
> +		if (!thread->hw_brk[i].address)
> +			return i;
> +	}
> +	return -1;
> +}
> +
>   long ppc_set_hwdebug(struct task_struct *child, struct ppc_hw_breakpoint *bp_info)
>   {
> +	int i;
>   #ifdef CONFIG_HAVE_HW_BREAKPOINT
>   	int len = 0;
>   	struct thread_struct *thread = &child->thread;
> @@ -223,15 +240,16 @@ long ppc_set_hwdebug(struct task_struct *child, struct ppc_hw_breakpoint *bp_inf
>   	if (bp_info->addr_mode != PPC_BREAKPOINT_MODE_EXACT)
>   		return -EINVAL;
>   
> -	if (child->thread.hw_brk.address)
> +	i = find_empty_hw_brk(&child->thread);
> +	if (i < 0)
>   		return -ENOSPC;
>   
>   	if (!ppc_breakpoint_available())
>   		return -ENODEV;
>   
> -	child->thread.hw_brk = brk;
> +	child->thread.hw_brk[i] = brk;
>   
> -	return 1;
> +	return i + 1;
>   }
>   
>   long ppc_del_hwdebug(struct task_struct *child, long data)
> @@ -241,7 +259,7 @@ long ppc_del_hwdebug(struct task_struct *child, long data)
>   	struct thread_struct *thread = &child->thread;
>   	struct perf_event *bp;
>   #endif /* CONFIG_HAVE_HW_BREAKPOINT */
> -	if (data != 1)
> +	if (data < 1 || data > nr_wp_slots())
>   		return -EINVAL;
>   
>   #ifdef CONFIG_HAVE_HW_BREAKPOINT
> @@ -254,11 +272,11 @@ long ppc_del_hwdebug(struct task_struct *child, long data)
>   	}
>   	return ret;
>   #else /* CONFIG_HAVE_HW_BREAKPOINT */
> -	if (child->thread.hw_brk.address == 0)
> +	if (child->thread.hw_brk[data - 1].address == 0)
>   		return -ENOENT;
>   
> -	child->thread.hw_brk.address = 0;
> -	child->thread.hw_brk.type = 0;
> +	child->thread.hw_brk[data - 1].address = 0;
> +	child->thread.hw_brk[data - 1].type = 0;
>   #endif /* CONFIG_HAVE_HW_BREAKPOINT */
>   
>   	return 0;
> diff --git a/arch/powerpc/kernel/ptrace/ptrace32.c b/arch/powerpc/kernel/ptrace/ptrace32.c
> index 7976ddf29c0e..7589a9665ffb 100644
> --- a/arch/powerpc/kernel/ptrace/ptrace32.c
> +++ b/arch/powerpc/kernel/ptrace/ptrace32.c
> @@ -259,8 +259,8 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
>   		ret = put_user(child->thread.debug.dac1, (u32 __user *)data);
>   #else
>   		dabr_fake = (
> -			(child->thread.hw_brk.address & (~HW_BRK_TYPE_DABR)) |
> -			(child->thread.hw_brk.type & HW_BRK_TYPE_DABR));
> +			(child->thread.hw_brk[0].address & (~HW_BRK_TYPE_DABR)) |
> +			(child->thread.hw_brk[0].type & HW_BRK_TYPE_DABR));
>   		ret = put_user(dabr_fake, (u32 __user *)data);
>   #endif
>   		break;
> diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
> index bbf237f072d4..b559b114d03d 100644
> --- a/arch/powerpc/kernel/signal.c
> +++ b/arch/powerpc/kernel/signal.c
> @@ -107,6 +107,9 @@ static void do_signal(struct task_struct *tsk)
>   	struct ksignal ksig = { .sig = 0 };
>   	int ret;
>   	int is32 = is_32bit_task();
> +#ifndef CONFIG_PPC_ADV_DEBUG_REGS
> +	int i;
> +#endif >
>   	BUG_ON(tsk != current);
>   
> @@ -128,8 +131,10 @@ static void do_signal(struct task_struct *tsk)
>   	 * user space. The DABR will have been cleared if it
>   	 * triggered inside the kernel.
>   	 */
> -	if (tsk->thread.hw_brk.address && tsk->thread.hw_brk.type)
> -		__set_breakpoint(&tsk->thread.hw_brk, 0);
> +	for (i = 0; i < nr_wp_slots(); i++) {
> +		if (tsk->thread.hw_brk[i].address && tsk->thread.hw_brk[i].type)
> +			__set_breakpoint(&tsk->thread.hw_brk[i], i);
> +	}

thread.hwbrk also exists when CONFIG_PPC_ADV_DEBUG_REGS is selected.

You could replace the #ifndef CONFIG_PPC_ADV_DEBUG_REGS by an if 
(!IS_ENABLED(CONFIG_PPC_ADV_DEBUG_REGS)) and then no need of an ifdef 
when declaring the int i;

>   #endif
>   	/* Re-enable the breakpoints for the signal stack */
>   	thread_change_pc(tsk, tsk->thread.regs);
> 

Christophe