[PATCH] Use delayed disable mode of ioapic edge triggered interrupts

[Eric W. Biederman]

Linus Torvalds <torvalds@xxxxxxxx> writes:

> Of course, for edge-triggered APIC interrupts, we _have_ to replay the irq 
> (since we don't have any way of even *knowing* whether we might get it 
> again), but for level-triggered and for the old legacy i8259 controller 
> that gets it right for edges anwyay, we should _not_ send the spurious 
> interrupt that is no longer active.
>
> And a lot of code has been tested with either just the i8259 (old machines 
> without any APIC) or with PCI-only devices (which are always level- 
> triggered), so the fact that edge-triggered things have always seen the 
> potential for spurious interrupts is not a reasong to say "well, they have 
> to handle it anyway". True PCI drivers generally do _not_ have to handle 
> the crazy case, and generally have never seen it.
>
> In other words, I think we should just make APIC-edge have the "please 
> delay masking and replay" bit, and nobody else.
>
> Can you send that patch (for both x86 and x86-64), and we can ask Komuro 
> to test it. That would be the "same behaviour as we've always had" thing, 
> which I think is also the _right_ behaviour.

Hopefully this is the trivial patch that solves the problem.

Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>

diff --git a/arch/i386/kernel/io_apic.c b/arch/i386/kernel/io_apic.c
index ad84bc2..3b7a63e 100644
--- a/arch/i386/kernel/io_apic.c
+++ b/arch/i386/kernel/io_apic.c
@@ -1287,9 +1287,11 @@ static void ioapic_register_intr(int irq
 			trigger == IOAPIC_LEVEL)
 		set_irq_chip_and_handler_name(irq, &ioapic_chip,
 					 handle_fasteoi_irq, "fasteoi");
-	else
+	else {
+		irq_desc[irq].status |= IRQ_DELAYED_DISABLE;
 		set_irq_chip_and_handler_name(irq, &ioapic_chip,
 					 handle_edge_irq, "edge");
+	}
 	set_intr_gate(vector, interrupt[irq]);
 }
 
diff --git a/arch/x86_64/kernel/io_apic.c b/arch/x86_64/kernel/io_apic.c
index 41bfc49..14654e6 100644
--- a/arch/x86_64/kernel/io_apic.c
+++ b/arch/x86_64/kernel/io_apic.c
@@ -790,9 +790,11 @@ static void ioapic_register_intr(int irq
 			trigger == IOAPIC_LEVEL)
 		set_irq_chip_and_handler_name(irq, &ioapic_chip,
 					      handle_fasteoi_irq, "fasteoi");
-	else
+	else {
+		irq_desc[irq].status |= IRQ_DELAYED_DISABLE;
 		set_irq_chip_and_handler_name(irq, &ioapic_chip,
 					      handle_edge_irq, "edge");
+	}
 }
 
 static void __init setup_IO_APIC_irqs(void)

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