Re: [PATCH 1/2] arm64: Reduce add_map() complexity

Oliver Graute
2023-08-01T08:55:25Z

On 14/02/23, Ying-Chun Liu (PaulLiu) wrote:
> From: Marc Zyngier <maz@kernel.org>
>
> In the add_map() function, for each level it populates, it iterates from
> the root of the PT tree, making it ineficient if a mapping needs to occur
> past level 1.
>
> Instead, replace it with a recursive (and much simpler) algorithm
> that keeps the complexity as low as possible. With this, mapping
> 512GB at level 2 goes from several seconds down to not measurable
> on an A55 machine.
>
> We keep the block mappings at level 1 for now though.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
> [ Paul: pick from the Android tree. Fixup Pierre's commit. Rebase to the
> upstream ]
> Signed-off-by: Ying-Chun Liu (PaulLiu) <paul.liu@linaro.org>
> Cc: Tom Rini <trini@konsulko.com>
> Link: https://android.googlesource.com/platform/external/u-boot/+/96ad729cf4cab53bdff8222bb3eb256f38b5c3a6
> Link: https://android.googlesource.com/platform/external/u-boot/+/6be9330601d81545c7c941e3609f35bf68a09059

Hello Marc,

this patch somehow broke the boot of my imx8qm board. I run into this
issue:

U-Boot 2023.07-rc6-00004-g5527698481 (Aug 01 2023 - 10:10:52 +0200)

Model: Advantech iMX8QM DMSSE20
Board: DMS-SE20A1 8GB
Build: SCFW 549b1e18, SECO-FW c9de51c0, ATF 5782363
Boot: USB
DRAM: 8 GiB
"Error" handler, esr 0xbf000000
elr: 0000000080020938 lr : 00000000800209c8 (reloc)
elr: 00000000ffecf938 lr : 00000000ffecf9c8
x0 : 0000000000000001 x1 : 0000000060000000
x2 : 0000000010000000 x3 : 0000000000000002
x4 : 0000000040000000 x5 : 0060000000000401
x6 : 0000000000000800 x7 : 00000000fff44a60
x8 : 0068000000000481 x9 : 0000000000000008
x10: 000000000a200023 x11: 0000000000000002
x12: 0000000000000002 x13: 0000000080095a00
x14: 00000000ffffffff x15: 00000000ffecfd2c
x16: 000000008005454c x17: 0000000000000000
x18: 00000000fd6afd50 x19: 000000000fe00000
x20: 0000000000000000 x21: 0060000000000401
x22: 0000000060200000 x23: 0000000000200000
x24: 0000000040000808 x25: 00000000001fffff
x26: 0000000000000003 x27: 0000000060200000
x28: 0000000000000002 x29: 00000000fd6ab110

Code: a94573fb a8c67bfd d65f03c0 b9418a40 (8a160334)
Resetting CPU ...

resetting ...
SCI reboot request............................................................................................................................................................................................................................

After some bisecting this patch poped up:

41e2787f5ec4249cb2e77a3ebd3c49035e3c6535 is the first bad commit
arm64: Reduce add_map() complexity

After I reverted everything on top of this patch its booting again with v2023.07

commit c1da6fdb5c239b432440721772d993e63cfdeb20
armv8: enable HAFDBS for other ELx when FEAT_HAFDBS is present

commit 836b8d4b205d2175b57cb9ef271e638b0c116e89
arm64: Use level-2 for largest block mappings when FEAT_HAFDBS is present

commit 6cdf6b7a340db4ddd008516181de7e08e3f8c213
arm64: Use FEAT_HAFDBS to track dirty pages when available

Do you have any idea whats going on here?

Best Regards,

Oliver