linux-kernel - Re: [v5.4 stable] arm: stm32: Regression observed on "no-map" reserved memory region

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Date:   Wed, 12 May 2021 12:55:53 +0200
From:   Alexandre TORGUE <alexandre.torgue@...s.st.com>
To:     Quentin Perret <qperret@...gle.com>
CC:     Florian Fainelli <f.fainelli@...il.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sasha Levin <sashal@...nel.org>,
        stable <stable@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        KarimAllah Ahmed <karahmed@...zon.de>,
        Android Kernel Team <kernel-team@...roid.com>,
        Architecture Mailman List <boot-architecture@...ts.linaro.org>,
        Frank Rowand <frowand.list@...il.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [v5.4 stable] arm: stm32: Regression observed on "no-map"
 reserved memory region

Hi Quentin,

On 5/10/21 12:09 PM, Quentin Perret wrote:
> Hi Alexandre,
> 
> On Friday 07 May 2021 at 17:15:20 (+0200), Alexandre TORGUE wrote:
>> Did you get time to continue some tests on this issue ?
> 
> I did try a few things, but still fail to reproduced :/
> 
>> On my side this DT is not working:
>>
>> memory@...00000 {
>>          reg = <0xc0000000 0x20000000>;
>> };
>>
>> reserved-memory {
>>          #address-cells = <1>;
>>          #size-cells = <1>;
>>          ranges;
>>
>>          gpu_reserved: gpu@...00000 {
>>                  reg = <0xd4000000 0x4000000>;
>>                  no-map;
>>          };
>> };
> 
> So this does change how memory appears in /proc/iomem for me switching
> from 5.4.101 to v5.4.102 -- for the former d4000000-d7ffffff doesn't
> appear at all, and for the latter it appears as 'reserved'.
> 
> But still, it never gets accounted as System RAM for me ...
> 
>> Let me know if I can help.
> 
> Could you please confirm you get a correct behaviour with 5.10.31 like
> Florian? If so, then bisecting to figure out what we're missing in older
> LTSes would help, but again it feels like we should just revert -- this
> wasn't really a fix in the first place.


We saw that patches [1] and [2] cause issue on stable version (at least 
for 5.4). As you said issue can be seen with above device tree and check 
in /proc/iomem than gpu_reserved region is taken by the kernel as 
"System RAM".

On v5.10 stream there are no issues seen taking patches [1]&[2] and the 
reason is linked to patches [3]&[4] which have been introduced in 
v5.10.0. Reverting them give me the same behavior than on stable version.


[1] of/fdt: Make sure no-map does not remove already reserved regions
[2] fdt: Properly handle "no-map" field in the memory region
[3] arch, drivers: replace for_each_membock() with for_each_mem_range()
[4] memblock: use separate iterators for memory and reserved regions

regards
Alex

> 
> Thanks,
> Quentin
>