Re: [PATCH v3 1/9] powerpc/watchpoint: Fix 512 byte boundary limit

From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Jordan Niethe <jniethe5@gmail.com>,
	Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>,
	mikey@neuling.org, apopple@linux.ibm.com,
	Paul Mackerras <paulus@samba.org>,
	Nicholas Piggin <npiggin@gmail.com>,
	Christophe Leroy <christophe.leroy@c-s.fr>,
	naveen.n.rao@linux.vnet.ibm.com, peterz@infradead.org,
	jolsa@kernel.org, oleg@redhat.com, fweisbec@gmail.com,
	mingo@kernel.org, pedromfc@br.ibm.com, miltonm@us.ibm.com,
	linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/9] powerpc/watchpoint: Fix 512 byte boundary limit
Date: Wed, 8 Jul 2020 09:52:45 +0200	[thread overview]
Message-ID: <2e418e64-e40a-f33d-8a1f-8f09a4605db9@csgroup.eu> (raw)
In-Reply-To: <CACzsE9qka0j7vKm186Z70fhNy9L4dNR3B97-jQ2oZZAwYduaRw@mail.gmail.com>

Le 08/07/2020 à 09:44, Jordan Niethe a écrit :
> On Wed, Jul 8, 2020 at 2:53 PM Ravi Bangoria
> <ravi.bangoria@linux.ibm.com> wrote:
>>
>> Milton Miller reported that we are aligning start and end address to
>> wrong size SZ_512M. It should be SZ_512. Fix that.
>>
>> While doing this change I also found a case where ALIGN() comparison
>> fails. Within a given aligned range, ALIGN() of two addresses does not
>> match when start address is pointing to the first byte and end address
>> is pointing to any other byte except the first one. But that's not true
>> for ALIGN_DOWN(). ALIGN_DOWN() of any two addresses within that range
>> will always point to the first byte. So use ALIGN_DOWN() instead of
>> ALIGN().
>>
>> Fixes: e68ef121c1f4 ("powerpc/watchpoint: Use builtin ALIGN*() macros")
>> Reported-by: Milton Miller <miltonm@us.ibm.com>
>> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
>> ---
>>   arch/powerpc/kernel/hw_breakpoint.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
>> index 0000daf0e1da..031e6defc08e 100644
>> --- a/arch/powerpc/kernel/hw_breakpoint.c
>> +++ b/arch/powerpc/kernel/hw_breakpoint.c
>> @@ -419,7 +419,7 @@ static int hw_breakpoint_validate_len(struct arch_hw_breakpoint *hw)
>>          if (dawr_enabled()) {
>>                  max_len = DAWR_MAX_LEN;
>>                  /* DAWR region can't cross 512 bytes boundary */
>> -               if (ALIGN(start_addr, SZ_512M) != ALIGN(end_addr - 1, SZ_512M))
>> +               if (ALIGN_DOWN(start_addr, SZ_512) != ALIGN_DOWN(end_addr - 1, SZ_512))
> I wonder if you should use end_addr - 1, but rather end_addr. For example:
> 512 -> 1023, because of the -1, 1024 will now be included in this
> range meaning 513 bytes?

end_addr is not part of the range.

If you want the range [512;1023], it means addr 512 len 512, that is 
end_addr = addr + len = 1024

Christophe