Re: [PATCH] powerpc: Fix the corrupt r3 error during MCE handling.

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Anshuman Khandual <khandual@linux.vnet.ibm.com> writes:

> 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.

huh??

(gdb) p/t 0x3ull << 62
$4 = 1100000000000000000000000000000000000000000000000000000000000000

Why you need an extra comment to explain 62. But yes, we can possibly
write that this is an RTAS bug

-aneesh