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

From: Quentin Perret <[email-masked]>
Date: Wed, 21 Apr 2021 08:31:00 +0000

On Tuesday 20 Apr 2021 at 09:33:56 (-0700), Florian Fainelli wrote:
> I do wonder as well, we have a 32MB "no-map" reserved memory region on
> our platforms located at 0xfe000000. Without the offending commit,
> /proc/iomem looks like this:
> 
> 40000000-fdffefff : System RAM
>   40008000-40ffffff : Kernel code
>   41e00000-41ef1d77 : Kernel data
> 100000000-13fffffff : System RAM
> 
> and with the patch applied, we have this:
> 
> 40000000-fdffefff : System RAM
>   40008000-40ffffff : Kernel code
>   41e00000-41ef3db7 : Kernel data
> fdfff000-ffffffff : System RAM
> 100000000-13fffffff : System RAM
> 
> so we can now see that the region 0xfe000000 - 0xfffffff is also cobbled
> up with the preceding region which is a mailbox between Linux and the
> secure monitor at 0xfdfff000 and of size 4KB. It seems like there is
> 
> The memblock=debug outputs is also different:
> 
> [    0.000000] MEMBLOCK configuration:
> [    0.000000]  memory size = 0xfdfff000 reserved size = 0x7ce4d20d
> [    0.000000]  memory.cnt  = 0x2
> [    0.000000]  memory[0x0]     [0x00000040000000-0x000000fdffefff],
> 0xbdfff000 bytes flags: 0x0
> [    0.000000]  memory[0x1]     [0x00000100000000-0x0000013fffffff],
> 0x40000000 bytes flags: 0x0
> [    0.000000]  reserved.cnt  = 0x6
> [    0.000000]  reserved[0x0]   [0x00000040003000-0x0000004000e494],
> 0xb495 bytes flags: 0x0
> [    0.000000]  reserved[0x1]   [0x00000040200000-0x00000041ef1d77],
> 0x1cf1d78 bytes flags: 0x0
> [    0.000000]  reserved[0x2]   [0x00000045000000-0x000000450fffff],
> 0x100000 bytes flags: 0x0
> [    0.000000]  reserved[0x3]   [0x00000047000000-0x0000004704ffff],
> 0x50000 bytes flags: 0x0
> [    0.000000]  reserved[0x4]   [0x000000c2c00000-0x000000fdbfffff],
> 0x3b000000 bytes flags: 0x0
> [    0.000000]  reserved[0x5]   [0x00000100000000-0x0000013fffffff],
> 0x40000000 bytes flags: 0x0
> 
> [    0.000000] MEMBLOCK configuration:
> [    0.000000]  memory size = 0x100000000 reserved size = 0x7ca4f24d
> [    0.000000]  memory.cnt  = 0x3
> [    0.000000]  memory[0x0]     [0x00000040000000-0x000000fdffefff],
> 0xbdfff000 bytes flags: 0x0
> [    0.000000]  memory[0x1]     [0x000000fdfff000-0x000000ffffffff],
> 0x2001000 bytes flags: 0x4
> [    0.000000]  memory[0x2]     [0x00000100000000-0x0000013fffffff],
> 0x40000000 bytes flags: 0x0
> [    0.000000]  reserved.cnt  = 0x6
> [    0.000000]  reserved[0x0]   [0x00000040003000-0x0000004000e494],
> 0xb495 bytes flags: 0x0
> [    0.000000]  reserved[0x1]   [0x00000040200000-0x00000041ef3db7],
> 0x1cf3db8 bytes flags: 0x0
> [    0.000000]  reserved[0x2]   [0x00000045000000-0x000000450fffff],
> 0x100000 bytes flags: 0x0
> [    0.000000]  reserved[0x3]   [0x00000047000000-0x0000004704ffff],
> 0x50000 bytes flags: 0x0
> [    0.000000]  reserved[0x4]   [0x000000c3000000-0x000000fdbfffff],
> 0x3ac00000 bytes flags: 0x0
> [    0.000000]  reserved[0x5]   [0x00000100000000-0x0000013fffffff],
> 0x40000000 bytes flags: 0x0
> 
> in the second case we can clearly see that the 32MB no-map region is now
> considered as usable RAM.
> 
> Hope this helps.
> 
> > 
> > In any case, the mere fact that this causes a regression should be
> > sufficient justification to revert/withdraw it from v5.4, as I don't
> > see a reason why it was merged there in the first place. (It has no
> > fixes tag or cc:stable)
> 
> Agreed, however that means we still need to find out whether a more
> recent kernel is also broken, I should be able to tell you that a little
> later.

FWIW I did test this on Qemu before posting. With 5.12-rc8 and a 1MiB
no-map region at 0x80000000, I have the following:

40000000-7fffffff : System RAM
  40210000-417fffff : Kernel code
  41800000-41daffff : reserved
  41db0000-4210ffff : Kernel data
  48000000-48008fff : reserved
80000000-800fffff : reserved
80100000-13fffffff : System RAM
  fa000000-ffffffff : reserved
  13b000000-13f5fffff : reserved
  13f6de000-13f77dfff : reserved
  13f77e000-13f77efff : reserved
  13f77f000-13f7dafff : reserved
  13f7dd000-13f7defff : reserved
  13f7df000-13f7dffff : reserved
  13f7e0000-13f7f3fff : reserved
  13f7f4000-13f7fdfff : reserved
  13f7fe000-13fffffff : reserved

If I remove the 'no-map' qualifier from DT, I get this:

40000000-13fffffff : System RAM
  40210000-417fffff : Kernel code
  41800000-41daffff : reserved
  41db0000-4210ffff : Kernel data
  48000000-48008fff : reserved
  80000000-800fffff : reserved
  fa000000-ffffffff : reserved
  13b000000-13f5fffff : reserved
  13f6de000-13f77dfff : reserved
  13f77e000-13f77efff : reserved
  13f77f000-13f7dafff : reserved
  13f7dd000-13f7defff : reserved
  13f7df000-13f7dffff : reserved
  13f7e0000-13f7f3fff : reserved
  13f7f4000-13f7fdfff : reserved
  13f7fe000-13fffffff : reserved

So this does seem to be working fine on my setup. I'll try again with
5.4 to see if I can repro.

Also, 8a5a75e5e9e5 ("of/fdt: Make sure no-map does not remove already
reserved regions") looks more likely to cause the issue observed here,
but that shouldn't be silent. I get the following error message in dmesg
if I if place the no-map region on top of the kernel image:

OF: fdt: Reserved memory: failed to reserve memory for node 'foobar@40210000': base 0x0000000040210000, size 1 MiB

Is that triggering on your end?

Thanks,
Quentin

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