On Thu, Jan 23, 2025 at 09:14:03AM +0100, Peter Zijlstra wrote:
> On Wed, Jan 22, 2025 at 12:47:20PM -0800, Josh Poimboeuf wrote:
> > What exactly do you mean by "NMI like"? Is it because a #DB might be
> > basically running in NMI context, if the NMI hit a breakpoint?
>
> No, #DB, #BP and such are considered NMI (and will have in_nmi() true)
> because they can trigger anywhere, including sections where IRQs are
> disabled.
So:
- while exceptions are technically not NMI, they're "NMI" because they
can occur in NMI or IRQ-disabled regions
- such "NMI" exceptions can be preempted by NMIs and "NMIs"
- NMIs can be preempted by "NMIs" but not NMIs (except in entry code!)
... did I get all that right? Not subtle at all!
I feel like in_nmi() needs a comment explaining all that nonobviousness.
--
Josh
