On Tue, Apr 12, 2016 at 12:23:35AM +0100, Ben Hutchings wrote: > On Wed, 2016-03-02 at 22:56 +0100, Radim Krčmář wrote: > > From: Radim Krčmář <rkrcmar@xxxxxxxxxx> > > > > commit 7dd0fdff145c5be7146d0ac06732ae3613412ac1 upstream. > > > > Discard policy uses ack_notifiers to prevent injection of PIT interrupts > > before EOI from the last one. > > > > This patch changes the policy to always try to deliver the interrupt, > > which makes a difference when its vector is in ISR. > > Old implementation would drop the interrupt, but proposed one injects to > > IRR, like real hardware would. > > > > The old policy breaks legacy NMI watchdogs, where PIT is used through > > virtual wire (LVT0): PIT never sends an interrupt before receiving EOI, > > thus a guest deadlock with disabled interrupts will stop NMIs. > > > > Note that NMI doesn't do EOI, so PIT also had to send a normal interrupt > > through IOAPIC. (KVM's PIT is deeply rotten and luckily not used much > > in modern systems.) > > > > Even though there is a chance of regressions, I think we can fix the > > LVT0 NMI bug without introducing a new tick policy. > [...] > > Given the 'chance of regressions', should we let this sit in mainline > longer before including it in stable updates? Hm, good point, Radim, what do you think, is this good to go to stable now? This has been in since 4.6-rc1, so it's been a few weeks with people running it already... thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html