linux-kernel - Re: [PATCH] powerpc/32s: Fix RTAS machine check with VMAP stack

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Date:   Wed, 23 Dec 2020 07:48:03 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/32s: Fix RTAS machine check with VMAP stack



Le 22/12/2020 à 08:11, Christophe Leroy a écrit :
> When we have VMAP stack, exception prolog 1 sets r1, not r11.

But exception prolog 1 uses r1 to setup r1 when machine check happens in kernel.
So r1 must be restored when the branch is not taken. See subsequent patch I just sent out.

Christophe

> 
> Fixes: da7bb43ab9da ("powerpc/32: Fix vmap stack - Properly set r1 before activating MMU")
> Fixes: d2e006036082 ("powerpc/32: Use SPRN_SPRG_SCRATCH2 in exception prologs")
> Cc: stable@...r.kernel.org
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>   arch/powerpc/kernel/head_book3s_32.S | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/head_book3s_32.S b/arch/powerpc/kernel/head_book3s_32.S
> index 349bf3f0c3af..fbc48a500846 100644
> --- a/arch/powerpc/kernel/head_book3s_32.S
> +++ b/arch/powerpc/kernel/head_book3s_32.S
> @@ -260,9 +260,16 @@ __secondary_hold_acknowledge:
>   MachineCheck:
>   	EXCEPTION_PROLOG_0
>   #ifdef CONFIG_PPC_CHRP
> +#ifdef CONFIG_VMAP_STACK
> +	mtspr	SPRN_SPRG_SCRATCH2,r1
> +	mfspr	r1, SPRN_SPRG_THREAD
> +	lwz	r1, RTAS_SP(r1)
> +	cmpwi	cr1, r1, 0
> +#else
>   	mfspr	r11, SPRN_SPRG_THREAD
>   	lwz	r11, RTAS_SP(r11)
>   	cmpwi	cr1, r11, 0
> +#endif
>   	bne	cr1, 7f
>   #endif /* CONFIG_PPC_CHRP */
>   	EXCEPTION_PROLOG_1 for_rtas=1
>