linux-kernel - Re: [PATCH] powerpc/chrp: Fix enter_rtas() with CONFIG_VMAP

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Date:   Mon, 17 Feb 2020 09:40:08 +1100
From:   Michael Neuling <mikey@...ling.org>
To:     Christophe Leroy <christophe.leroy@....fr>,
        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/chrp: Fix enter_rtas() with CONFIG_VMAP_STACK

On Fri, 2020-02-14 at 08:33 +0000, Christophe Leroy wrote:
> With CONFIG_VMAP_STACK, data MMU has to be enabled
> to read data on the stack.

Can you describe what goes wrong without this? Some oops message? rtas blows up?
Get corrupt data?

Also can you say what you're actually doing (ie turning on MSR[DR])


> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> ---
>  arch/powerpc/kernel/entry_32.S | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
> index 0713daa651d9..bc056d906b51 100644
> --- a/arch/powerpc/kernel/entry_32.S
> +++ b/arch/powerpc/kernel/entry_32.S
> @@ -1354,12 +1354,17 @@ _GLOBAL(enter_rtas)
>  	mtspr	SPRN_SRR0,r8
>  	mtspr	SPRN_SRR1,r9
>  	RFI
> -1:	tophys(r9,r1)
> +1:	tophys_novmstack r9, r1
> +#ifdef CONFIG_VMAP_STACK
> +	li	r0, MSR_KERNEL & ~MSR_IR	/* can take DTLB miss */

You're potentially turning on more than MSR DR here. This should be clear in the
commit message.

> +	mtmsr	r0
> +	isync
> +#endif
>  	lwz	r8,INT_FRAME_SIZE+4(r9)	/* get return address */
>  	lwz	r9,8(r9)	/* original msr value */
>  	addi	r1,r1,INT_FRAME_SIZE
>  	li	r0,0
> -	tophys(r7, r2)
> +	tophys_novmstack r7, r2
>  	stw	r0, THREAD + RTAS_SP(r7)
>  	mtspr	SPRN_SRR0,r8
>  	mtspr	SPRN_SRR1,r9