On Fri, 2011-09-02 at 14:50 -0700, Jeremy Fitzhardinge wrote: > On 09/02/2011 01:47 PM, Peter Zijlstra wrote: > > On Fri, 2011-09-02 at 12:29 -0700, Jeremy Fitzhardinge wrote: > >>> I know that its generally considered bad form, but there's at least one > >>> spinlock that's only taken from NMI context and thus hasn't got any > >>> deadlock potential. > >> Which one? > > arch/x86/kernel/traps.c:nmi_reason_lock > > > > It serializes NMI access to the NMI reason port across CPUs. > > Ah, OK. Well, that will never happen in a PV Xen guest. But PV > ticketlocks are equally applicable to an HVM Xen domain (and KVM guest), > so I guess there's at least some chance there could be a virtual > emulated NMI. Maybe? Does qemu do that kind of thing? Afaik qemu/kvm can do the whole NMI thing, yes. > But, erm, does that even make sense? I'm assuming the NMI reason port > tells the CPU why it got an NMI. If multiple CPUs can get NMIs and > there's only a single reason port, then doesn't that mean that either 1) > they all got the NMI for the same reason, or 2) having a single port is > inherently racy? How does the locking actually work there? I really wouldn't know, the whole NMI thing is a bit of a trainwreck architecturally. Maybe the x86 maintainers or Linus knows more on this aspect of it. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
