linux-kernel - Re: [PATCH v2] powerpc/powermac: Fix low_sleep_handler with CONFIG_VMAP

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Date:   Tue, 08 Dec 2020 09:30:50 +0100
From:   Giuseppe Sacco <giuseppe@...azz.it>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2] powerpc/powermac: Fix low_sleep_handler with
 CONFIG_VMAP_STACK

Hello Christophe,

Il giorno mar, 08/12/2020 alle 05.24 +0000, Christophe Leroy ha
scritto:
> low_sleep_handler() can't restore the context from standard
> stack because the stack can hardly be accessed with MMU OFF.
> 
> Store everything in a global storage area instead of storing
> a pointer to the stack in that global storage area.
> 
> To avoid a complete churn of the function, still use r1 as
> the pointer to the storage area during restore.
> 
> Reported-by: Giuseppe Sacco <giuseppe@...azz.it>
> Fixes: cd08f109e262 ("powerpc/32s: Enable CONFIG_VMAP_STACK")
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
> This is only build tested. Giuseppe can you test it ? Thanks.
> 
> v2: Changed an erroneous 'addis' to 'addi' ; Using bss instead of
> data section
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  arch/powerpc/platforms/Kconfig.cputype  |   2 +-
>  arch/powerpc/platforms/powermac/sleep.S | 132 +++++++++++-----------
> --
>  2 files changed, 60 insertions(+), 74 deletions(-)
[...]

I just tested the v2 patch against latest kernel. Please note that
yesterday patch was on a kernel named 5.10.0-rc6+, while today's patch
is on a kernel named 5.10.0-rc7+. Even with the latest kernel updates,
the patch apply correctly and machine boots normally, fixing the
problem.

$ uname -a
Linux titanium4 5.10.0-rc7+ #3 Tue Dec 8 09:11:20 CET 2020 ppc GNU/Linux
$ grep VMAP /boot/config-5.10.0-rc7+
CONFIG_HAVE_ARCH_VMAP_STACK=y
CONFIG_VMAP_STACK=y

Thank you again.

Bye,
Giuseppe