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? Ben. -- Ben Hutchings This sentence contradicts itself - no actually it doesn't.
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