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Date:   Mon, 30 Mar 2020 22:38:02 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Subject: Re: [PATCH 10/12] powerpc/entry32: Blacklist exception entry points
 for kprobe.
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Christophe Leroy <christophe.leroy@c-s.fr>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Paul Mackerras <paulus@samba.org>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
References: <dff05b59a161434a546010507000816750073f28.1585474724.git.christophe.leroy@c-s.fr>
        <aea027844b12fcbc29ea78d26c5848a6794d1688.1585474724.git.christophe.leroy@c-s.fr>
In-Reply-To: <aea027844b12fcbc29ea78d26c5848a6794d1688.1585474724.git.christophe.leroy@c-s.fr>
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Christophe Leroy wrote:
> kprobe does not handle events happening in real mode.
> 
> As exception entry points are running with MMU disabled,
> blacklist them.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
>  arch/powerpc/kernel/entry_32.S | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
> index 94f78c03cb79..9a1a45d6038a 100644
> --- a/arch/powerpc/kernel/entry_32.S
> +++ b/arch/powerpc/kernel/entry_32.S
> @@ -51,6 +51,7 @@ mcheck_transfer_to_handler:
>  	mfspr	r0,SPRN_DSRR1
>  	stw	r0,_DSRR1(r11)
>  	/* fall through */
> +_ASM_NOKPROBE_SYMBOL(mcheck_transfer_to_handler)
> 
>  	.globl	debug_transfer_to_handler
>  debug_transfer_to_handler:
> @@ -59,6 +60,7 @@ debug_transfer_to_handler:
>  	mfspr	r0,SPRN_CSRR1
>  	stw	r0,_CSRR1(r11)
>  	/* fall through */
> +_ASM_NOKPROBE_SYMBOL(debug_transfer_to_handler)
> 
>  	.globl	crit_transfer_to_handler
>  crit_transfer_to_handler:
> @@ -94,6 +96,7 @@ crit_transfer_to_handler:
>  	rlwinm	r0,r1,0,0,(31 - THREAD_SHIFT)
>  	stw	r0,KSP_LIMIT(r8)
>  	/* fall through */
> +_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler)
>  #endif
> 
>  #ifdef CONFIG_40x
> @@ -115,6 +118,7 @@ crit_transfer_to_handler:
>  	rlwinm	r0,r1,0,0,(31 - THREAD_SHIFT)
>  	stw	r0,KSP_LIMIT(r8)
>  	/* fall through */
> +_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler)
>  #endif
> 
>  /*
> @@ -127,6 +131,7 @@ crit_transfer_to_handler:
>  	.globl	transfer_to_handler_full
>  transfer_to_handler_full:
>  	SAVE_NVGPRS(r11)
> +_ASM_NOKPROBE_SYMBOL(transfer_to_handler_full)
>  	/* fall through */
> 
>  	.globl	transfer_to_handler
> @@ -286,6 +291,8 @@ reenable_mmu:
>  	lwz	r2, GPR2(r11)
>  	b	fast_exception_return
>  #endif
> +_ASM_NOKPROBE_SYMBOL(transfer_to_handler)
> +_ASM_NOKPROBE_SYMBOL(transfer_to_handler_cont)

These are added after 'reenable_mmu', which is itself not blacklisted.  
Is that intentional?


- Naveen