[RFT PATCH] ARM: suspend: switch to swapper_pg_dir before using the vmap'ed stack

[Ard Biesheuvel]

On Fri, 7 Jan 2022 at 10:15, Geert Uytterhoeven <geert at linux-m68k.org> wrote:
>
> Hi Ard,
>
> On Thu, Jan 6, 2022 at 8:27 PM Ard Biesheuvel <ardb at kernel.org> wrote:
> > The resume from suspend code switches to the ID map so it can enable the
> > MMU. On !LPAE configurations, the ID map carries its own copy of the
> > kernel VA range, but this is not kept in sync with swapper_pg_dir, and
> > so it may lack the mapping of the kernel mode stack if CONFIG_VMAP_STACK
> > is enabled.
> >
> > So let's switch to swapper_pg_dir right after re-enabling the MMU on
> > such configurations. This avoids a crash on resume observed on various
> > platforms [0].
> >
> > [0] https://lore.kernel.org/linux-arm-kernel/20211122092816.2865873-8-ardb@kernel.org/
> >
> > Cc: Marek Szyprowski <m.szyprowski at samsung.com>
> > Cc: Geert Uytterhoeven <geert at linux-m68k.org>
> > Cc: Jon Hunter <jonathanh at nvidia.com>
> > Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
>
> Thanks for your patch!
>
> This fixes s2ram on r8a7791/koelsch (dual Cortex-A15) with
> shmobile_defconfig.
> S2ram on sh73a0/kzm9g (dual Cortex-A9) works as before.
>
> Tested-by: Geert Uytterhoeven <geert+renesas at glider.be>
>

Thanks Geert.

> > ---
> > Please test with the Kconfig patch [9177/1] reverted.
> >
> >  arch/arm/kernel/sleep.S | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/arch/arm/kernel/sleep.S b/arch/arm/kernel/sleep.S
> > index b062b3738bc6..6217ef90feb0 100644
> > --- a/arch/arm/kernel/sleep.S
> > +++ b/arch/arm/kernel/sleep.S
> > @@ -119,6 +119,13 @@ ENTRY(cpu_resume_mmu)
> >  ENDPROC(cpu_resume_mmu)
> >         .popsection
> >  cpu_resume_after_mmu:
> > +#if defined(CONFIG_VMAP_STACK) && !defined(CONFIG_ARM_LPAE)
> > +       @ Before using the vmap'ed stack, we have to switch to swapper_pg_dir
> > +       @ as the ID map does not cover the vmalloc region.
> > +       mrc     p15, 0, ip, c2, c0, 1   @ read TTBR1
> > +       mcr     p15, 0, ip, c2, c0, 0   @ set TTBR0
> > +       isb
> > +#endif
> >         bl      cpu_init                @ restore the und/abt/irq banked regs
> >         mov     r0, #0                  @ return zero on success
> >         ldmfd   sp!, {r4 - r11, pc}
>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds