Intel's definition of "edge triggered" means: "asserted with a low-to-high transition at the time an interrupt is registered and then kept high until the interrupt is served via one of the EOI mechanisms or goes away unhandled." So the only difference between edge triggered and level triggered is in the leading edge, with no difference in the trailing edge. This bug manifested itself when the guest was Microport UNIX System V/386 v2.1 (ca. 1987), because it would sometimes mask off IRQ14 in the slave IMR after it had already been asserted. The master would still try to deliver an interrupt even though IRQ2 had dropped again, resulting in a spurious interupt (IRQ15) and a panicked UNIX kernel. Signed-off-by: Matthew Ogilvie <mmogilvi_qemu@xxxxxxxxxxxx> --- There has been some discussions about this on the qemu mailing list; for example see http://www.mail-archive.com/qemu-devel@xxxxxxxxxx/msg129071.html This fixes the test program I wrote to demonstrate the problem. See http://home.comcast.net/~mmogilvi/downloads/i8259-imr-test-2012-09-02.tar.bz2 (for source code to a floppy disk boot sector) or a kvm-unit-test patch I'm posting separately. Unfortunately, Microport UNIX still has some some unknown interrupt problem when run under qemu with KVM enabled, although it runs fine under plain QEMU [no KVM] with the corresponding QEMU patch. The unknown interrupt bug actually triggers much earlier than this one: this one doesn't show up until the boot floppy accesses the hard drive after some prompts, but the unknown bug shows up early in bootup. Also, the specific function in which UNIX panics is different: this one in splint(); the unknown bug in splx(). Also, the KVM behavior is not affected by the presense or absense of this patch. I'll probably continue looking into the unknown problem, but I'm not sure when I'll have any results. Despite this unknown problem, I'm confident that this known problem should be fixed, and if not fixed will cause problems when I figure out the unknown problem. arch/x86/kvm/i8254.c | 6 +++++- arch/x86/kvm/i8259.c | 14 ++++++-------- 2 files changed, 11 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c index adba28f..5cbba99 100644 --- a/arch/x86/kvm/i8254.c +++ b/arch/x86/kvm/i8254.c @@ -302,8 +302,12 @@ static void pit_do_work(struct kthread_work *work) } spin_unlock(&ps->inject_lock); if (inject) { - kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 1); + /* Clear previous interrupt, then create a rising + * edge to request another interupt, and leave it at + * level=1 until time to inject another one. + */ kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 0); + kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 1); /* * Provides NMI watchdog support via Virtual Wire mode. diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c index e498b18..b0c2346 100644 --- a/arch/x86/kvm/i8259.c +++ b/arch/x86/kvm/i8259.c @@ -111,8 +111,10 @@ static inline int pic_set_irq1(struct kvm_kpic_state *s, int irq, int level) s->irr |= mask; } s->last_irr |= mask; - } else + } else { + s->irr &= ~mask; s->last_irr &= ~mask; + } return (s->imr & mask) ? -1 : ret; } @@ -169,14 +171,10 @@ static void pic_update_irq(struct kvm_pic *s) { int irq2, irq; + /* slave PIC notifies master PIC via IRQ2 */ irq2 = pic_get_irq(&s->pics[1]); - if (irq2 >= 0) { - /* - * if irq request by slave pic, signal master PIC - */ - pic_set_irq1(&s->pics[0], 2, 1); - pic_set_irq1(&s->pics[0], 2, 0); - } + pic_set_irq1(&s->pics[0], 2, irq2 >= 0); + irq = pic_get_irq(&s->pics[0]); pic_irq_request(s->kvm, irq >= 0); } -- 1.7.10.2.484.gcd07cc5 -- 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
