Re: [PATCH]x86_64 debug_stack nested patch (again)

["bibo,mao" <bibo.mao@intel.com>]

Sorry for late reply, interrupt is disabled when int3/int1 trap happens 
and NMI is not permitted for kprobe in x86_64 platform,nest level of kprobe 
is 2 at most. So that will work well if DEBUG_STACK is set to 8K when CONFIG_KPROBE
option is set.

Thanks
bibo,mao

Andi Kleen wrote:
> On Thursday 11 May 2006 13:17, Andrew Morton wrote:
>> "bibo,mao" <bibo.mao@intel.com> wrote:
>>> Hi,
>>> In x86_64 platform, INT1 and INT3 trap stack is IST stack called DEBUG_STACK,
>>> when INT1/INT3 trap happens, system will switch to DEBUG_STACK by hardware. 
>>> Current DEBUG_STACK size is 4K, when int1/int3 trap happens, kernel will 
>>> minus current DEBUG_STACK IST value by 4k. But if int3/int1 trap is nested, 
>>> it will destroy other vector's IST stack. This patch modifies this, it sets 
>>> DEBUG_STACK size as 8K and allows two level of nested int1/int3 trap.
>>>
>>> Kprobe DEBUG_STACK may be nested, because kprobe hanlder may be probed 
>>> by other kprobes. This patch is against 2.6.17-rc3. Thanks jbeulich for pointing out error in the first patch.
>>>
>>> Signed-Off-By: bibo, mao <bibo.mao@intel.com>
>>>
>>> --- 2.6.17-rc3.org/include/asm-x86_64/page.h	2006-05-10 12:07:18.000000000 +0800
>>> +++ 2.6.17-rc3/include/asm-x86_64/page.h	2006-05-10 12:19:24.000000000 +0800
>>> @@ -20,7 +20,7 @@
>>>  #define EXCEPTION_STACK_ORDER 0
>>>  #define EXCEPTION_STKSZ (PAGE_SIZE << EXCEPTION_STACK_ORDER)
>>>  
>>> -#define DEBUG_STACK_ORDER EXCEPTION_STACK_ORDER
>>> +#define DEBUG_STACK_ORDER (EXCEPTION_STACK_ORDER + 1)
>>>  #define DEBUG_STKSZ (PAGE_SIZE << DEBUG_STACK_ORDER)
>>>  
>>>  #define IRQSTACK_ORDER 2
>> So....   why not do it this way?
> 
> Last time we discussed this I was told it could nest upto 3 or 4 times
> So that still wouldn't work.
> 
> If anything they should decrease the int3/debug stack to 2K, then 8K 
> might be enough.
> 
> Or even better would be to fix kprobes to not do that.
> 
> I think paranoidentry would need to be fixed for that too.
> 
> -Andi
> 
> -
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