linux-kernel - Re: [PATCH] ARM, xtensa: highmem: avoid clobbering non-page aligned memory reservations

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Message-ID: <20201031154528.GA14628@kernel.org>
Date:   Sat, 31 Oct 2020 17:45:28 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        linux-xtensa@...ux-xtensa.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Chris Zankel <chris@...kel.net>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Max Filippov <jcmvbkbc@...il.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM, xtensa: highmem: avoid clobbering non-page aligned
 memory reservations

On Sat, Oct 31, 2020 at 12:21:24PM +0100, Ard Biesheuvel wrote:
> On Sat, 31 Oct 2020 at 12:04, Russell King - ARM Linux admin
> <linux@...linux.org.uk> wrote:
> >
> > On Sat, Oct 31, 2020 at 11:47:42AM +0100, Ard Biesheuvel wrote:
> > > On Sat, 31 Oct 2020 at 11:33, Russell King - ARM Linux admin
> > > <linux@...linux.org.uk> wrote:
> > > >
> > > > On Sat, Oct 31, 2020 at 11:43:45AM +0200, Mike Rapoport wrote:
> > > > > From: Ard Biesheuvel <ardb@...nel.org>
> > > > >
> > > > > free_highpages() iterates over the free memblock regions in high
> > > > > memory, and marks each page as available for the memory management
> > > > > system.
> > > > >
> > > > > Until commit cddb5ddf2b76 ("arm, xtensa: simplify initialization of
> > > > > high memory pages") it rounded beginning of each region upwards and end of
> > > > > each region downwards.
> > > > >
> > > > > However, after that commit free_highmem() rounds the beginning and end of
> > > > > each region downwards, and we may end up freeing a page that is
> > > > > memblock_reserve()d, resulting in memory corruption.
> > > > >
> > > > > Restore the original rounding of the region boundaries to avoid freeing
> > > > > reserved pages.
> > > > >
> > > > > Fixes: cddb5ddf2b76 ("arm, xtensa: simplify initialization of high memory pages")
> > > > > Link: https://lore.kernel.org/r/20201029110334.4118-1-ardb@kernel.org/
> > > > > Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> > > > > Co-developed-by:  Mike Rapoport <rppt@...ux.ibm.com>
> > > > > Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> > > > > ---
> > > > >
> > > > > Max, Russell,
> > > > >
> > > > > Please let me know how do you prefer to take it upstream.
> > > > > If needed this can go via memblock tree.
> > > > >
> > > > > v2: fix words order in the commit message
> > > >
> > > > I really don't understand what is going on here; there seems to be a
> > > > total disconnect of communication between yourself and Ard. Ard has
> > > > already submitted a different patch for this to the patch system
> > > > already, sent yesterday.
> > > >
> > > > https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9021/1
> > > >
> > > > Please discuss between yourselves how you want to solve the problem,
> > > > and then submit an agreed and tested patch to those of us upstream;
> > > > please don't make it for those upstream to pick one of your patches
> > > > as you are at present.
> > > >
> > >
> > > Apologies for creating this confusion. I posted a patch and dropped it
> > > into the patch system when I found the bug.
> > >
> > > However, only when Florian asked about a 'fixes' tag, I went back to
> > > the history, and realized that the issue was introduced by Mike during
> > > the most recent merge window, and affects xtensa as well.
> >
> > So why does Mike's patch have:
> >
> > Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> >
> > in it? It seems you haven't been directly involved in Mike's patch.
> >
> 
> Because I cc'ed him on the discussion following the patch that is now
> in your patch system. So he took that patch and modified it, but
> retained the original S-o-b and authorship.

Right, that's exactly what happened.

> > There's something /really/ not right with the process behind this
> > patch.
> >
> > > I don't have a preference which patch gets applied, though, so please
> > > indicate your preference, and we will adapt accordingly.
> >
> > I asked for you both to come to a concensus about how you want to
> > proceed, and now you're throwing it back on to me to solve your(pl)
> > mis-communication issue. We haven't heard from Mike yet.
> >
> 
> I am not throwing it back to you. I merely indicated that I have no
> preference, and since Mike is the one who introduced this issue in the
> first place, I am expecting him to drive this. And indeed, we haven't
> heard from him yet.

I didn't know that Ard's patch was already in the patch system. I took
the patch from the list, updated it, added a fix for xtensa and resend
while retaining Ard's authourship and s-o-b.

> > Clearly, I wasn't blunt and stroppy enough to be properly understood.
> > Sort it out between yourselves and tell me which patch you want me to
> > apply.
> >
> 
> I would like you to ack this version of the patch, and disregard the
> one in the patch system, so that Mike can take this one through the
> memblock tree where the issue originated in the first place.

Agree.

-- 
Sincerely yours,
Mike.