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Diffstat (limited to 'arch/x86_64/kernel/io_apic.c')
-rw-r--r--arch/x86_64/kernel/io_apic.c58
1 files changed, 56 insertions, 2 deletions
diff --git a/arch/x86_64/kernel/io_apic.c b/arch/x86_64/kernel/io_apic.c
index 1c6c6f72457..050141c0602 100644
--- a/arch/x86_64/kernel/io_apic.c
+++ b/arch/x86_64/kernel/io_apic.c
@@ -152,6 +152,32 @@ static inline void io_apic_modify(unsigned int apic, unsigned int value)
writel(value, &io_apic->data);
}
+static int io_apic_level_ack_pending(unsigned int irq)
+{
+ struct irq_pin_list *entry;
+ unsigned long flags;
+ int pending = 0;
+
+ spin_lock_irqsave(&ioapic_lock, flags);
+ entry = irq_2_pin + irq;
+ for (;;) {
+ unsigned int reg;
+ int pin;
+
+ pin = entry->pin;
+ if (pin == -1)
+ break;
+ reg = io_apic_read(entry->apic, 0x10 + pin*2);
+ /* Is the remote IRR bit set? */
+ pending |= (reg >> 14) & 1;
+ if (!entry->next)
+ break;
+ entry = irq_2_pin + entry->next;
+ }
+ spin_unlock_irqrestore(&ioapic_lock, flags);
+ return pending;
+}
+
/*
* Synchronize the IO-APIC and the CPU by doing
* a dummy read from the IO-APIC
@@ -1418,9 +1444,37 @@ static void ack_apic_level(unsigned int irq)
ack_APIC_irq();
/* Now we can move and renable the irq */
- move_masked_irq(irq);
- if (unlikely(do_unmask_irq))
+ if (unlikely(do_unmask_irq)) {
+ /* Only migrate the irq if the ack has been received.
+ *
+ * On rare occasions the broadcast level triggered ack gets
+ * delayed going to ioapics, and if we reprogram the
+ * vector while Remote IRR is still set the irq will never
+ * fire again.
+ *
+ * To prevent this scenario we read the Remote IRR bit
+ * of the ioapic. This has two effects.
+ * - On any sane system the read of the ioapic will
+ * flush writes (and acks) going to the ioapic from
+ * this cpu.
+ * - We get to see if the ACK has actually been delivered.
+ *
+ * Based on failed experiments of reprogramming the
+ * ioapic entry from outside of irq context starting
+ * with masking the ioapic entry and then polling until
+ * Remote IRR was clear before reprogramming the
+ * ioapic I don't trust the Remote IRR bit to be
+ * completey accurate.
+ *
+ * However there appears to be no other way to plug
+ * this race, so if the Remote IRR bit is not
+ * accurate and is causing problems then it is a hardware bug
+ * and you can go talk to the chipset vendor about it.
+ */
+ if (!io_apic_level_ack_pending(irq))
+ move_masked_irq(irq);
unmask_IO_APIC_irq(irq);
+ }
}
static struct irq_chip ioapic_chip __read_mostly = {