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

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Message-ID: <65909c25-71b2-0116-1ac7-a56118bca86e@gmail.com>
Date:   Wed, 19 Aug 2020 17:32:35 -0700
From:   Doug Berger <opendmb@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Florian Fainelli <f.fainelli@...il.com>
Cc:     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 8/19/2020 10:40 AM, Andrew Morton wrote:
> 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.
> 
As Florian guessed, I assumed the Fixes: tag was a sufficient clue since
I wouldn't normally apply a Fixes tag to a typo correction in a comment.
I suspect I have been spoiled by David Miller :).

Thanks for the quick turn-around and applying the cc:stable to the mmotm,
    Doug