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

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Date:   Tue, 20 Aug 2019 09:30:17 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Alastair D'Silva <alastair@....ibm.com>, 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

On Fri, Aug 16, 2019 at 09:14:12AM +0200, Greg Kroah-Hartman wrote:
> On Fri, Aug 16, 2019 at 11:42:22AM +1000, Michael Ellerman wrote:
> > 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 :)
> 
> That is exactly what you should have done.  It needs to be VERY explicit
> as to why this is being submitted different from what upstream did, and
> to what trees it needs to go to and who is going to be responsible for
> when it breaks.  And it will break :)

And it needs to be done before I can apply it, I've dropped this thread
from my queue now.

thanks,

greg k-h