2020-04-01 06:15:20

by Ravi Bangoria

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

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 <[email protected]>
---
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++) {
+ 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);
+ }
+ }
}
#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);
+ }
#endif
/* Re-enable the breakpoints for the signal stack */
thread_change_pc(tsk, tsk->thread.regs);
--
2.21.1

2020-04-01 06:57:52

by Christophe Leroy

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

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 <[email protected]>
> ---
> 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

2020-04-01 09:18:28

by Ravi Bangoria

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

>>   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;

Yes that's better.

[...]

>> +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);
>

Sure.

[...]

>> @@ -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;

Makes sense. Will change it.

Ravi