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

[bibo,mao]

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@xxxxxxxxx> 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@xxxxxxxxx>
> > >
> > > --- 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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