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

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.

quoted

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