linux-kernel - Re: [PATCH] powerpc: Allow flush_(inval_)dcache

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Message-ID: <87mug97uo1.fsf@concordia.ellerman.id.au>
Date:   Fri, 16 Aug 2019 11:42:22 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alastair D'Silva <alastair@....ibm.com>
Cc:     alastair@...ilva.org, stable@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Allison Randal <allison@...utok.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc: Allow flush_(inval_)dcache_range to work across ranges >4GB

Greg Kroah-Hartman <gregkh@...uxfoundation.org> writes:
> On Thu, Aug 15, 2019 at 02:55:42PM +1000, Alastair D'Silva wrote:
>> From: Alastair D'Silva <alastair@...ilva.org>
>> 
>> Heads Up: This patch cannot be submitted to Linus's tree, as the affected
>> assembler functions have already been converted to C.

That was done in upstream commit:

22e9c88d486a ("powerpc/64: reuse PPC32 static inline flush_dcache_range()")

Which is a larger change that we don't want to backport. This patch is a
minimal fix for stable trees.


>> When calling flush_(inval_)dcache_range with a size >4GB, we were masking
>> off the upper 32 bits, so we would incorrectly flush a range smaller
>> than intended.
>> 
>> This patch replaces the 32 bit shifts with 64 bit ones, so that
>> the full size is accounted for.
>> 
>> Signed-off-by: Alastair D'Silva <alastair@...ilva.org>
>> ---
>>  arch/powerpc/kernel/misc_64.S | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)

Acked-by: Michael Ellerman <mpe@...erman.id.au>

> <formletter>
>
> This is not the correct way to submit patches for inclusion in the
> stable kernel tree.  Please read:
>     https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> for how to do this properly.
>
> </formletter>

Hi Greg,

This is "option 3", submit the patch directly, and the patch "deviates
from the original upstream patch" because the upstream patch was a
wholesale conversion from asm to C.

This patch applies cleanly to v4.14 and v4.19.

The change log should have mentioned which upstream patch it is not a
backport of, is there anything else we should have done differently to
avoid the formletter bot :)

cheers