Re: [PATCH 1/3] x86/entry/64: Refactor IRQ stacks and make then NMI-safe

[Andy Lutomirski]

On Fri, Jul 24, 2015 at 9:16 PM, Borislav Petkov <bp@xxxxxxxxx> wrote:
> On Fri, Jul 24, 2015 at 11:02:51AM -0700, Andy Lutomirski wrote:
>> So really the only difference between this simple approach (which is
>> more or less what we do now) and my fancy approach is that a kernel
>> instruction breakpoint will cause do_debug to run on the initial stack
>> instead of the IRQ stack.
>
> Sounds ok to me. What would be the worst thing if we limited the #DB
> stack? Some breakpoints will get ignored? In an endless stream of
> breakpoints hammering? Doesn't sound like a valid use case to me, does
> it?
>
>> I'm still tempted to say we should use my overly paranoid atomic
>> approach for now and optimize later,...
>
> But why change it if the simple approach of incrementing irq_count first
> is still fine? I think we want to KISS here exactly because apparently
> complexity in that area is a serious PITA...

Yeah, I'm going to submit v2 with the simple approach.  I admit I'm
rather fond of xadd as a way to switch rsp and set a flag at the same
time, though :)

--Andy
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