linux-kernel - Re: [PATCH v2 13/16] powerpc/watchpoint: Prepare handler to handle more than one watcnhpoint

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Message-Id: <cb2c250b-c963-45fe-f3b4-879076c495ab@linux.ibm.com>
Date:   Wed, 1 Apr 2020 14:43:41 +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 13/16] powerpc/watchpoint: Prepare handler to handle
 more than one watcnhpoint



On 4/1/20 12:20 PM, Christophe Leroy wrote:
> 
> 
> Le 01/04/2020 à 08:13, Ravi Bangoria a écrit :
>> Currently we assume that we have only one watchpoint supported by hw.
>> Get rid of that assumption and use dynamic loop instead. This should
>> make supporting more watchpoints very easy.
>>
>> With more than one watchpoint, exception handler need to know which
>> DAWR caused the exception, and hw currently does not provide it. So
>> we need sw logic for the same. To figure out which DAWR caused the
>> exception, check all different combinations of user specified range,
>> dawr address range, actual access range and dawrx constrains. For ex,
>> if user specified range and actual access range overlaps but dawrx is
>> configured for readonly watchpoint and the instruction is store, this
>> DAWR must not have caused exception.
>>
>> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
>> ---
>>   arch/powerpc/include/asm/processor.h |   2 +-
>>   arch/powerpc/include/asm/sstep.h     |   2 +
>>   arch/powerpc/kernel/hw_breakpoint.c  | 396 +++++++++++++++++++++------
>>   arch/powerpc/kernel/process.c        |   3 -
>>   4 files changed, 313 insertions(+), 90 deletions(-)
>>
> 
> [...]
> 
>> -static bool
>> -dar_range_overlaps(unsigned long dar, int size, struct arch_hw_breakpoint *info)
>> +static bool dar_user_range_overlaps(unsigned long dar, int size,
>> +                    struct arch_hw_breakpoint *info)
>>   {
>>       return ((dar <= info->address + info->len - 1) &&
>>           (dar + size - 1 >= info->address));
>>   }
> 
> Here and several other places, I think it would be more clear if you could avoid the - 1 :
> 
>      return ((dar < info->address + info->len) &&
>          (dar + size > info->address));

Ok. see below...

> 
> 
>> +static bool dar_in_hw_range(unsigned long dar, struct arch_hw_breakpoint *info)
>> +{
>> +    unsigned long hw_start_addr, hw_end_addr;
>> +
>> +    hw_start_addr = ALIGN_DOWN(info->address, HW_BREAKPOINT_SIZE);
>> +    hw_end_addr = ALIGN(info->address + info->len, HW_BREAKPOINT_SIZE) - 1;
>> +
>> +    return ((hw_start_addr <= dar) && (hw_end_addr >= dar));
>> +}
> 
>      hw_end_addr = ALIGN(info->address + info->len, HW_BREAKPOINT_SIZE);
> 
>      return ((hw_start_addr <= dar) && (hw_end_addr > dar));

I'm using -1 while calculating end address is to make it
inclusive. If I don't use -1, the end address points to a
location outside of actual range, i.e. it's not really an
end address.

Ravi