linux-kernel - Re: [PATCH v2 09/16] powerpc/watchpoint: Convert thread_struct->hw

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Date:   Wed, 1 Apr 2020 14:36:21 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     mpe@...erman.id.au, mikey@...ling.org, apopple@...ux.ibm.com,
        paulus@...ba.org, npiggin@...il.com,
        naveen.n.rao@...ux.vnet.ibm.com, peterz@...radead.org,
        jolsa@...nel.org, oleg@...hat.com, fweisbec@...il.com,
        mingo@...nel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
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