[PATCH] ARM: Fix userspace enter on LPAE with CC_OPTIMIZE_FOR_SIZE=y

[Linus Walleij]

On Wed, May 15, 2024 at 4:02 PM Geert Uytterhoeven
<geert+renesas at glider.be> wrote:

> Booting an LPAE-enabled kernel built with CONFIG_CC_OPTIMIZE_FOR_SIZE=y
> fails when starting userspace:
>
>     Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000004
>     CPU: 1 PID: 1 Comm: init Tainted: G        W        N 6.9.0-rc1-koelsch-00004-g7af5b901e847 #1930
>     Hardware name: Generic R-Car Gen2 (Flattened Device Tree)
>     Call trace:
>      unwind_backtrace from show_stack+0x10/0x14
>      show_stack from dump_stack_lvl+0x78/0xa8
>      dump_stack_lvl from panic+0x118/0x398
>      panic from do_exit+0x1ec/0x938
>      do_exit from sys_exit_group+0x0/0x10
>     ---[ end Kernel panic - not syncing: Attempted to kill init!  exitcode=0x00000004 ]---
>
> Add the missing memory clobber to cpu_set_ttbcr(), as suggested by
> Russell King.
>
> Force inlining of uaccess_save_and_enable(), as suggested by Ard
> Biesheuvel.
>
> The latter fixes booting on Koelsch.
>
> Fixes: 7af5b901e84743c6 ("ARM: 9358/2: Implement PAN for LPAE by TTBR0 page table walks disablement")
> Closes: https://lore.kernel.org/r/CAMuHMdWTAJcZ9BReWNhpmsgkOzQxLNb5OhNYxzxv6D5TSh2fwQ@mail.gmail.com/
> Signed-off-by: Geert Uytterhoeven <geert+renesas at glider.be>

Reviewed-by: Linus Walleij <linus.walleij at linaro.org>

Thanks for digging into this, both you and Ard! And we found the root
cause it seems.

Yours,
Linus Walleij