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List:       oprofile-commits
Subject:    Re: [oprof-cvs] [PATCH] oprofile: use KM_NMI slot for kmap_atomic
From:       Junxiao Bi <junxiao.bi () oracle ! com>
Date:       2012-08-22 8:03:44
Message-ID: 50349260.3010608 () oracle ! com
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On 08/22/2012 03:07 PM, Robert Richter wrote:
> On 22.08.12 10:21:07, Junxiao Bi wrote:
>> If one kernel path is using KM_USER0 slot and is interrupted by
>> the oprofile nmi, then in copy_from_user_nmi(), the KM_USER0 slot
>> will be overwrite and cleared to zero at last, when the control
>> return to the original kernel path, it will access an invalid
>> virtual address and trigger a crash.
>>
>> Cc: Robert Richter <robert.richter@amd.com>
>> Cc: Greg KH <gregkh@linuxfoundation.org>
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
>>
>> Hi, Please review this patch.
>>
>> It is for linux-2.6.32.y stable branch not for mainline.
> I am not sure if there will be any .32 stable release in the future,
> but this could be at least for .34 or if there is one for .27 and .35.
>
>> Thanks,
>> Junxiao.
>> ---
>>  arch/x86/oprofile/backtrace.c |    4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
> We should implement the perf version here, which does a:
>
> 	int type = in_nmi() ? KM_NMI : KM_IRQ0;
>
> See arch/x86/kernel/cpu/perf_event.c.
KM_NMI seems OK for this since this function is only called by oprofile
backtrace which is in nmi context.
> -Robert
>
>> diff --git a/arch/x86/oprofile/backtrace.c b/arch/x86/oprofile/backtrace.c
>> index 829edf0..b50a280 100644
>> --- a/arch/x86/oprofile/backtrace.c
>> +++ b/arch/x86/oprofile/backtrace.c
>> @@ -71,9 +71,9 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
>>  		offset = addr & (PAGE_SIZE - 1);
>>  		size = min(PAGE_SIZE - offset, n - len);
>>  
>> -		map = kmap_atomic(page, KM_USER0);
>> +		map = kmap_atomic(page, KM_NMI);
>>  		memcpy(to, map+offset, size);
>> -		kunmap_atomic(map, KM_USER0);
>> +		kunmap_atomic(map, KM_NMI);
>>  		put_page(page);
>>  
>>  		len  += size;
>> -- 
>> 1.7.9.5
>>
>>


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