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>

diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
index 1eddae94bab331bee8eb01b5e71fd6df8e0d7604..1150c6d5c7b893fdaebb73e8eb8b53ed0b41be5d 100644 (file)
--- 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);
                }
        }