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Subject: Re: [PATCH 07/15] powerpc/watchpoint: Get watchpoint count
 dynamically while disabling them
To:     Christophe Leroy <christophe.leroy@c-s.fr>
Cc:     mpe@ellerman.id.au, mikey@neuling.org, apopple@linux.ibm.com,
        paulus@samba.org, npiggin@gmail.com,
        naveen.n.rao@linux.vnet.ibm.com, peterz@infradead.org,
        jolsa@kernel.org, oleg@redhat.com, fweisbec@gmail.com,
        mingo@kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org,
        Ravi Bangoria <ravi.bangoria@linux.ibm.com>
References: <20200309085806.155823-1-ravi.bangoria@linux.ibm.com>
 <20200309085806.155823-8-ravi.bangoria@linux.ibm.com>
 <c73b77fd-b983-2c5c-75bb-4b2f47a94d92@c-s.fr>
 <cca28aeb-d1f8-5668-0743-2269f621e926@linux.ibm.com>
From:   Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Date:   Thu, 26 Mar 2020 09:02:05 +0530
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On 3/18/20 12:27 PM, Ravi Bangoria wrote:
> 
> 
> On 3/17/20 4:02 PM, Christophe Leroy wrote:
>>
>>
>> Le 09/03/2020 à 09:57, Ravi Bangoria a écrit :
>>> Instead of disabling only one watchpooint, get num of available
>>> watchpoints dynamically and disable all of them.
>>>
>>> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
>>> ---
>>>   arch/powerpc/include/asm/hw_breakpoint.h | 15 +++++++--------
>>>   1 file changed, 7 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/arch/powerpc/include/asm/hw_breakpoint.h b/arch/powerpc/include/asm/hw_breakpoint.h
>>> index 980ac7d9f267..ec61e2b7195c 100644
>>> --- a/arch/powerpc/include/asm/hw_breakpoint.h
>>> +++ b/arch/powerpc/include/asm/hw_breakpoint.h
>>> @@ -75,14 +75,13 @@ extern void ptrace_triggered(struct perf_event *bp,
>>>               struct perf_sample_data *data, struct pt_regs *regs);
>>>   static inline void hw_breakpoint_disable(void)
>>>   {
>>> -    struct arch_hw_breakpoint brk;
>>> -
>>> -    brk.address = 0;
>>> -    brk.type = 0;
>>> -    brk.len = 0;
>>> -    brk.hw_len = 0;
>>> -    if (ppc_breakpoint_available())
>>> -        __set_breakpoint(&brk, 0);
>>> +    int i;
>>> +    struct arch_hw_breakpoint null_brk = {0};
>>> +
>>> +    if (ppc_breakpoint_available()) {
>>
>> I think this test should go into nr_wp_slots() which should return zero when no breakpoint is available.
> 
> Seems possible. Will change it in next version.

Once we move ppc_breakpoint_available() logic into nr_wp_slots(),
'dawr_force_enable' variable is checked in nr_wp_slots() before
it gets initialized in dawr_force_setup():

     start_kernel()
     |-> perf_event_init()
     |     init_hw_breakpoint()
     |       hw_breakpoint_slots()
     |         nr_wp_slots()
     |           /* Check dawr_force_enable variable */
     |
     |-> arch_call_rest_init()
           rest_init()
             kernel_thread(kernel_init, ...)
               ...
                 kernel_init()
                   kernel_init_freeable()
                     ...
                     do_one_initcall()
                       dawr_force_setup()
                         /* Set dawr_force_enable = true */

Because of this, hw-breakpoint infrastructure is initialized with
no DAWRs. So I'm thinking to keep the code as it is i.e. not moving
ppc_breakpoint_available() test inside nr_wp_slots().

Ravi