KVM: Avoid redelivery of edge interrupt before next edge

The check for an edge is broken in current ioapic code. ioapic->irr is
cleared on each edge interrupt by ioapic_service() and this makes
old_irr != ioapic->irr condition in kvm_ioapic_set_irq() to be always
true. The patch fixes the code to properly recognise edge.

Some HW emulation calls set_irq() without level change. If each such
call is propagated to an OS it may confuse a device driver. This is the
case with keyboard device emulation and Windows XP x64  installer on SMP VM.
Each keystroke produce two interrupts (down/up) one interrupt is
submitted to CPU0 and another to CPU1. This confuses Windows somehow
and it ignores keystrokes.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
index 1eddae94bab3..1150c6d5c7b8 100644
--- a/virt/kvm/ioapic.c
+++ b/virt/kvm/ioapic.c
@@ -95,8 +95,6 @@ static int ioapic_service(struct kvm_ioapic *ioapic, unsigned int idx)
                 if (injected && pent->fields.trig_mode == IOAPIC_LEVEL_TRIG)
                         pent->fields.remote_irr = 1;
         }
-        if (!pent->fields.trig_mode)
-                ioapic->irr &= ~(1 << idx);
 
         return injected;
 }
@@ -136,7 +134,8 @@ static void ioapic_write_indirect(struct kvm_ioapic *ioapic, u32 val)
                 mask_after = ioapic->redirtbl[index].fields.mask;
                 if (mask_before != mask_after)
                         kvm_fire_mask_notifiers(ioapic->kvm, index, mask_after);
-                if (ioapic->irr & (1 << index))
+                if (ioapic->redirtbl[index].fields.trig_mode == IOAPIC_LEVEL_TRIG
+                    && ioapic->irr & (1 << index))
                         ioapic_service(ioapic, index);
                 break;
         }
@@ -184,9 +183,10 @@ int kvm_ioapic_set_irq(struct kvm_ioapic *ioapic, int irq, int level)
                 if (!level)
                         ioapic->irr &= ~mask;
                 else {
+                        int edge = (entry.fields.trig_mode == IOAPIC_EDGE_TRIG);
                         ioapic->irr |= mask;
-                        if ((!entry.fields.trig_mode && old_irr != ioapic->irr)
-                            || !entry.fields.remote_irr)
+                        if ((edge && old_irr != ioapic->irr) ||
+                            (!edge && !entry.fields.remote_irr))
                                 ret = ioapic_service(ioapic, irq);
                 }
         }