On Sat, Apr 30, 2016 at 12:11:45AM +0200, Jiri Kosina wrote:

On Fri, 29 Apr 2016, Andy Lutomirski wrote:

quoted

quoted

NMI, MCE and interrupts aren't a problem because they have dedicated
stacks, which are easy to detect.  If the tasks' stack is on an
exception stack or an irq stack, we consider it unreliable.

Only on x86_64.

Well, MCEs are more or less x86-specific as well. But otherwise good 
point, thanks Andy.

So, how does stack layout generally look like in case when NMI is actually 
running on proper kernel stack? I thought it's guaranteed to contain 
pt_regs anyway in all cases. Is that not guaranteed to be the case?

If the NMI were using the normal kernel stack and it interrupted kernel
space, pt_regs would be placed in the "middle" of the stack rather than
the bottom, and there's currently no way to detect that.

However, NMIs don't sleep, and we only consider sleeping tasks for stack
reliability, so it wouldn't be an issue anyway.

-- 
Josh