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Date: Thu, 11 Jul 2013 11:24:15 +0530
From: Anshuman Khandual <khandual@linux.vnet.ibm.com>
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To: Mahesh J Salgaonkar <mahesh@linux.vnet.ibm.com>
Subject: Re: [PATCH] powerpc: Fix the corrupt r3 error during MCE handling.
References: <20130710130155.4993.61577.stgit@mars>
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On 07/10/2013 06:32 PM, Mahesh J Salgaonkar wrote:
> From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
> 
> During Machine Check interrupt on pseries platform, R3 generally points to
> memory region inside RTAS (FWNMI) area. We see r3 corruption because when RTAS
> delivers the machine check exception it passes the address inside FWNMI area
> with the top most bit set. This patch fixes this issue by masking top two bit
> in machine check exception handler.
> 
> Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
> ---
>  arch/powerpc/platforms/pseries/ras.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/powerpc/platforms/pseries/ras.c b/arch/powerpc/platforms/pseries/ras.c
> index 7b3cbde..721c058 100644
> --- a/arch/powerpc/platforms/pseries/ras.c
> +++ b/arch/powerpc/platforms/pseries/ras.c
> @@ -287,6 +287,9 @@ static struct rtas_error_log *fwnmi_get_errinfo(struct pt_regs *regs)
>  	unsigned long *savep;
>  	struct rtas_error_log *h, *errhdr = NULL;
> 
> +	/* Mask top two bits */
> +	regs->gpr[3] &= ~(0x3UL << 62);

We need to replace this "62" with a shift macro specifying the significance
of these top two address bits in the real mode.