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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Nanyong Sun <sunnanyong@huawei.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        benh@kernel.crashing.org, paulus@samba.org,
        akpm@linux-foundation.org, npiggin@gmail.com,
        christophe.leroy@c-s.fr
Cc:     linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        wangkefeng 00584194 <wangkefeng.wang@huawei.com>
Subject: Re: [PATCH -next] powerpc/mm: check base flags in ioremap_prot
In-Reply-To: <e27f8786-7d43-4191-9b65-5a55a64cf158@huawei.com>
References: <20210903090339.3671524-1-sunnanyong@huawei.com>
 <90aa2b67-24c8-4a5f-d91a-b562054d5c5d@csgroup.eu>
 <e27f8786-7d43-4191-9b65-5a55a64cf158@huawei.com>
Date:   Sat, 04 Sep 2021 21:20:25 +1000
Message-ID: <87fsukzix2.fsf@mpe.ellerman.id.au>
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Nanyong Sun <sunnanyong@huawei.com> writes:
> On 2021/9/3 17:16, Christophe Leroy wrote:
>> Le 03/09/2021 =C3=A0 11:03, Nanyong Sun a =C3=A9crit=C2=A0:
>>> Some drivers who call ioremap_prot without setting base flags like
>>> ioremap_prot(addr, len, 0) may work well before
>>> commit 56f3c1413f5c ("powerpc/mm: properly set PAGE_KERNEL flags in
>>> ioremap()"), but now they will get a virtual address "successfully"
>>> from ioremap_prot and badly fault on memory access later because that
>>> patch also dropped the hack adding of base flags for ioremap_prot.
>>>
>>> So return NULL and throw a warning if the caller of ioremap_prot did
>>> not set base flags properly. Why not just hack adding PAGE_KERNEL flags
>>> in the ioremap_prot, because most scenarios can be covered by high level
>>> functions like ioremap(), ioremap_coherent(), ioremap_cache()...
>>> so it is better to keep max flexibility for this low level api.
>>
>> As far as I can see, there is no user of this fonction that sets flags=20
>> to 0 in the kernel tree.
>>
>> Did you find any ? If you did, I think it is better to fix the caller.
>>
>> Christophe
>>
> I see some vendor's drivers which are not on upstream ...

Sorry, but we don't carry extraneous checks in upstream for the sake of
out-of-tree drivers.

cheers