linux-kernel - Re: [v6,3/5] powerpc/book3e: support kgdb for kernel space

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Date:	Fri, 9 May 2014 14:36:14 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Tiejun Chen <tiejun.chen@...driver.com>
CC:	<linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [v6,3/5] powerpc/book3e: support kgdb for kernel space

On Wed, Oct 23, 2013 at 05:31:23PM +0800, Tiejun Chen wrote:
> Currently we need to skip this for supporting KGDB.
> 
> Signed-off-by: Tiejun Chen <tiejun.chen@...driver.com>
> 
> ---
> arch/powerpc/kernel/exceptions-64e.S |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
> index a55cf62..0b750c6 100644
> --- a/arch/powerpc/kernel/exceptions-64e.S
> +++ b/arch/powerpc/kernel/exceptions-64e.S
> @@ -597,11 +597,13 @@ kernel_dbg_exc:
>  	rfdi
>  
>  	/* Normal debug exception */
> +1:	andi.	r14,r11,MSR_PR;		/* check for userspace again */
> +#ifndef CONFIG_KGDB
>  	/* XXX We only handle coming from userspace for now since we can't
>  	 *     quite save properly an interrupted kernel state yet
>  	 */
> -1:	andi.	r14,r11,MSR_PR;		/* check for userspace again */
>  	beq	kernel_dbg_exc;		/* if from kernel mode */
> +#endif

Now that we have support for properly saving state on special level
exceptions, that should be used here.  With the above patch, what happens
if e.g. a debug exception fires during a TLB miss, and the kgdb handler
takes its own TLB miss accessing the serial port?

-Scott
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