linux-kernel - Re: [PATCH] powerpc/8xx: Fix permanently mapped IMMR region.

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Message-ID: <d22ac38c-0b03-fbc0-88d1-899e356fa487@c-s.fr>
Date:   Tue, 26 Nov 2019 08:01:13 +0000
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc/8xx: Fix permanently mapped IMMR region.

On 11/18/2019 11:17 AM, Michael Ellerman wrote:
> Christophe Leroy <christophe.leroy@....fr> writes:
>> When not using large TLBs, the IMMR region is still
>> mapped as a whole block in the FIXMAP area.
>>
>> Do not remove pages mapped in the FIXMAP region when
>> initialising paging.
>>
>> Properly report that the IMMR region is block-mapped even
>> when not using large TLBs.
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>> ---
>>   arch/powerpc/mm/mem.c        |  8 --------
>>   arch/powerpc/mm/nohash/8xx.c | 13 +++++++------
>>   2 files changed, 7 insertions(+), 14 deletions(-)
> 
> This blows up pmac32_defconfig + qemu mac99 for me with:
> 
>    NET: Registered protocol family 1
>    RPC: Registered named UNIX socket transport module.
>    RPC: Registered udp transport module.
>    RPC: Registered tcp transport module.
>    RPC: Registered tcp NFSv4.1 backchannel transport module.
>    PCI: CLS 0 bytes, default 32
>    Trying to unpack rootfs image as initramfs...
>    BUG: Unable to handle kernel data access on write at 0xfffdf000

I tested it with pmac32_defconfig and qemu mac99 and don't get the problem:

NET: Registered protocol family 1
RPC: Registered named UNIX socket transport module.
RPC: Registered udp transport module.
RPC: Registered tcp transport module.
RPC: Registered tcp NFSv4.1 backchannel transport module.
PCI: CLS 0 bytes, default 32
Initialise system trusted keyrings
workingset: timestamp_bits=30 max_order=15 bucket_order=0
NFS: Registering the id_resolver key type
Key type id_resolver registered
...

Looks like I don't get that 'Trying to unpack rootfs image as 
initramfs...', do you change anything to pmac32_defconfig ?

Anyway, when rebasing this patch on next branch, only the 
arch/powerpc/mm/nohash/8xx.c change remains. The other part is already 
applied through another patch.

So I believe the remaining part is safe to apply

Christophe