linux-kernel - Re: [PATCH v2] mm: include CMA pages in lowmem

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Date:   Wed, 19 Aug 2020 10:40:57 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Doug Berger <opendmb@...il.com>, Jason Baron <jbaron@...mai.com>,
        David Rientjes <rientjes@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm: include CMA pages in lowmem_reserve at boot

On Wed, 19 Aug 2020 10:30:25 -0700 Florian Fainelli <f.fainelli@...il.com> wrote:

> On 8/19/20 10:22 AM, Andrew Morton wrote:
> > On Wed, 19 Aug 2020 10:15:53 -0700 Florian Fainelli <f.fainelli@...il.com> wrote:
> > 
> >>>> In many cases the difference is not significant, but for example
> >>>> an ARM platform with 1GB of memory and the following memory layout
> >>>> [    0.000000] cma: Reserved 256 MiB at 0x0000000030000000
> >>>> [    0.000000] Zone ranges:
> >>>> [    0.000000]   DMA      [mem 0x0000000000000000-0x000000002fffffff]
> >>>> [    0.000000]   Normal   empty
> >>>> [    0.000000]   HighMem  [mem 0x0000000030000000-0x000000003fffffff]
> >>>>
> >>>> would result in 0 lowmem_reserve for the DMA zone. This would allow
> >>>> userspace to deplete the DMA zone easily.
> >>>
> >>> Sounds fairly serious for thos machines.  Was a cc:stable considered?
> >>
> >> Since there is a Fixes: tag, it may have been assumed that the patch
> >> would be picked up and as soon as it reaches Linus' tree it would be
> >> picked up by the stable selection.
> > 
> > It doesn't work that way - sometimes a fix isn't considered important
> > enough to backport.  It could just fix a typo in a comment!
> 
> Then can this be applied ASAP and back ported?

Sure.