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Date: Thu, 31 May 2012 17:38:48 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: "H. Peter Anvin" <hpa@...or.com> Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>, Andrew Morton <akpm@...ux-foundation.org>, Peter Zijlstra <peterz@...radead.org>, Frederic Weisbecker <fweisbec@...il.com>, Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>, Dave Jones <davej@...hat.com>, Andi Kleen <ak@...ux.intel.com> Subject: Re: [PATCH 4/5] x86: Allow nesting of the debug stack IDT setting On Thu, 2012-05-31 at 17:37 -0400, Steven Rostedt wrote: > On Thu, 2012-05-31 at 14:09 -0700, H. Peter Anvin wrote: > > > No, I'm asking what environments (alternate stacks) are permitted where. > > That is the important information. > > I believe that the IST stack switch is just a convenient way to allow > separate stacks for separate events instead of trying to handle all > events on a single stack, and risk stack overflow. > > Thus, the debug/int3 and NMI events use a separate stack to not stress > the current stack that is not expected to switch. The external interrupt > stacks are switched on entry of the interrupt and stays on that stack > and until its finished. There's a check to see if it is already on the > stack before it does the switch so that it doesn't have the HW switch > issues that NMI and int3 has. > > Thus, if we say we must stay on either the NMI stack or the DEBUG stack, > then this is what happens. Well, almost. > > For NMIs, if it preempted something on the debug stack, it will always > stay on the NMI stack and never switch. A check is made for both debug > stacks at once: > > int is_debug_stack(unsigned long addr) > { > return __get_cpu_var(debug_stack_usage) || > (addr <= __get_cpu_var(debug_stack_addr) && > addr > (__get_cpu_var(debug_stack_addr) - DEBUG_STKSZ)); > } > And, yes, I can send a patch to change these to this_cpu_() if you like ;-) -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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