[Qemu-devel] [RFC PATCH v2] qemu: x86: ignore ioapic polarity

["Gabriel L. Somlo" <gsomlo@gmail.com>]

Both QEMU and KVM have already accumulated a significant number of
optimizations based on the hard-coded assumption that ioapic polarity
will always use the ActiveHigh convention, where the logical and
physical states of level-triggered irq lines always match (i.e.,
active(asserted) == high == 1, inactive == low == 0). QEMU guests
are expected to follow directions given via ACPI and configure the
ioapic with polarity 0 (ActiveHigh). However, even when misbehaving
guests (e.g. OS X <= 10.9) set the ioapic polarity to 1 (ActiveLow),
QEMU will still use the ActiveHigh signaling convention when
interfacing with the emulated ioapic.

This patch modifies the emulated ioapic to completely ignore polarity
as set by the guest OS, enabling misbehaving guests to work alongside
those which comply with the ActiveHigh polarity specified by QEMU's
ACPI tables.

Signed-off-by: Gabriel L. Somlo <somlo@cmu.edu>
---

> OK, this would "harmonize" TCG with KVM, in terms of acknowledging
> the realities of hard-coded ActiveHigh behavior throughout the rest
> of the code base.

Now with a new and improved commit blurb :)

Thanks,
  Gabriel

 hw/intc/ioapic.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/hw/intc/ioapic.c b/hw/intc/ioapic.c
index 652dd47..b527932 100644
--- a/hw/intc/ioapic.c
+++ b/hw/intc/ioapic.c
@@ -93,9 +93,6 @@ static void ioapic_set_irq(void *opaque, int vector, int level)
         uint32_t mask = 1 << vector;
         uint64_t entry = s->ioredtbl[vector];
 
-        if (entry & (1 << IOAPIC_LVT_POLARITY_SHIFT)) {
-            level = !level;
-        }
         if (((entry >> IOAPIC_LVT_TRIGGER_MODE_SHIFT) & 1) ==
             IOAPIC_TRIGGER_LEVEL) {
             /* level triggered */
-- 
1.8.1.4