linux-kernel - Re: [PATCH v2] powerpc/32s: fix BATs setting with CONFIG_STRICT_KERNEL

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Message-ID: <47f3caee-510b-a95c-cf08-013a282141b6@c-s.fr>
Date:   Wed, 1 May 2019 19:22:06 +0200
From:   christophe leroy <christophe.leroy@....fr>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Serge Belyshev <belyshev@...ni.sinp.msu.ru>,
        Segher Boessenkool <segher@...nel.crashing.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2] powerpc/32s: fix BATs setting with
 CONFIG_STRICT_KERNEL_RWX



Le 01/05/2019 à 02:55, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@....fr> writes:
>> Serge reported some crashes with CONFIG_STRICT_KERNEL_RWX enabled
>> on a book3s32 machine.
>>
>> Analysis shows two issues:
>> - BATs addresses and sizes are not properly aligned.
>> - There is a gap between the last address covered by BATs and the
>> first address covered by pages.
>>
>> Memory mapped with DBATs:
>> 0: 0xc0000000-0xc07fffff 0x00000000 Kernel RO coherent
>> 1: 0xc0800000-0xc0bfffff 0x00800000 Kernel RO coherent
>> 2: 0xc0c00000-0xc13fffff 0x00c00000 Kernel RW coherent
>> 3: 0xc1400000-0xc23fffff 0x01400000 Kernel RW coherent
>> 4: 0xc2400000-0xc43fffff 0x02400000 Kernel RW coherent
>> 5: 0xc4400000-0xc83fffff 0x04400000 Kernel RW coherent
>> 6: 0xc8400000-0xd03fffff 0x08400000 Kernel RW coherent
>> 7: 0xd0400000-0xe03fffff 0x10400000 Kernel RW coherent
>>
>> Memory mapped with pages:
>> 0xe1000000-0xefffffff  0x21000000       240M        rw       present           dirty  accessed
>>
>> This patch fixes both issues. With the patch, we get the following
>> which is as expected:
>>
>> Memory mapped with DBATs:
>> 0: 0xc0000000-0xc07fffff 0x00000000 Kernel RO coherent
>> 1: 0xc0800000-0xc0bfffff 0x00800000 Kernel RO coherent
>> 2: 0xc0c00000-0xc0ffffff 0x00c00000 Kernel RW coherent
>> 3: 0xc1000000-0xc1ffffff 0x01000000 Kernel RW coherent
>> 4: 0xc2000000-0xc3ffffff 0x02000000 Kernel RW coherent
>> 5: 0xc4000000-0xc7ffffff 0x04000000 Kernel RW coherent
>> 6: 0xc8000000-0xcfffffff 0x08000000 Kernel RW coherent
>> 7: 0xd0000000-0xdfffffff 0x10000000 Kernel RW coherent
>>
>> Memory mapped with pages:
>> 0xe0000000-0xefffffff  0x20000000       256M        rw       present           dirty  accessed
>>
>> Reported-by: Serge Belyshev <belyshev@...ni.sinp.msu.ru>
>> Fixes: 63b2bc619565 ("powerpc/mm/32s: Use BATs for STRICT_KERNEL_RWX")
>> Cc: stable@...r.kernel.org
> 
> I could probably still get this into v5.1 if you're confident it's a
> good fix.

If possible it would be great.

Yes I'm confident it is a good fix:
- The fix has no impact on the configurations I tested originally (they 
were lacking a trailing area not mapped with BATs and the boundarie 
between RW and RO was a power of 2 so ffs() returned the same as lfs())
- The fix was tested by myself on QEMU.
- The fix was tested by Serge.
- The fix was acked by Segher.
- The fix make sense (ie ffs() is the good one, fls() was definitly wrong)

Christophe

> 
> cheers
> 

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