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From: Bernhard Kohl <>
Subject: [PATCH] KVM: IOAPIC: Do not check polarity
Date: Fri, 13 Mar 2009 10:53:02 +0000 (UTC)	[thread overview]
Message-ID: <> (raw)

NSN's proprietary OS DMX heavily depends on a correct BIOS MP table.
>From there it also gets the information for initialization of PCI
devices. We defined the polarity and trigger mode as for standard
PCI devices "low level". The OS programs the ioapic the same way.

Nothing else in QEMU's and KVM's IRQ, PIC, IOAPIC and LAPIC code
cares about interrupt polarity. The "level" is always used as a
logical value. So we must not change the level here. If we do so,
PCI low level interrupts are not fired if the guest raises the
interrupt (level=1), but first if it is reset again (level=0). This
can result in infinite waiting for a single interupt. For example
the DMX guest waits for the link up interupt of the E1000
ethernet device before enabling the TX and RX interupts of
this device. E1000 emulation sets level=1, no interrupt is fired,

This does not happen if we use the -no-kvm-irqchip option.
This means that qemu's ioapic does not care about the polarity and
kvm's ioapic shouldn't do either.

Signed-off-by: Bernhard Kohl <>
 virt/kvm/ioapic.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
index 1eddae9..4deb8e1 100644
--- a/virt/kvm/ioapic.c
+++ b/virt/kvm/ioapic.c
@@ -180,7 +180,6 @@ int kvm_ioapic_set_irq(struct kvm_ioapic *ioapic, int irq,
int level)
 	if (irq >= 0 && irq < IOAPIC_NUM_PINS) {
 		entry = ioapic->redirtbl[irq];
-		level ^= entry.fields.polarity;
 		if (!level)
 			ioapic->irr &= ~mask;
 		else {

             reply	other threads:[~2009-03-13 10:53 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-03-13 10:53 Bernhard Kohl [this message]
2009-03-15 10:38 ` [PATCH] KVM: IOAPIC: Do not check polarity Avi Kivity
2009-03-16 22:30   ` Bernhard Kohl

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