[RFC PATCH 06/23] x86/ioapic: Add support for IRQCHIP_CAN_DELIVER_AS_NMI with interrupt remapping

[Ricardo Neri]

Even though there is a delivery mode field at the entries of an IO APIC's
redirection table, the documentation of the majority of the IO APICs
explicitly states that interrupt delivery as non-maskable is not supported.
Thus,

However, when using an IO APIC in combination with the Intel VT-d interrupt
remapping functionality, the delivery of the interrupt to the CPU is
handled by the remapping hardware. In such a case, the interrupt can be
delivered as non maskable.

Thus, add the IRQCHIP_CAN_DELIVER_AS_NMI flag only when used in combination
with interrupt remapping.

Cc: Ashok Raj <ashok.raj@xxxxxxxxx>
Cc: Andi Kleen <andi.kleen@xxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Jacob Pan <jacob.jun.pan@xxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Dou Liyang <douly.fnst@xxxxxxxxxxxxxx>
Cc: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Cc: "Ravi V. Shankar" <ravi.v.shankar@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
 arch/x86/kernel/apic/io_apic.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 10a20f8..39de91b 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -1911,7 +1911,8 @@ static struct irq_chip ioapic_ir_chip __read_mostly = {
 	.irq_eoi		= ioapic_ir_ack_level,
 	.irq_set_affinity	= ioapic_set_affinity,
 	.irq_retrigger		= irq_chip_retrigger_hierarchy,
-	.flags			= IRQCHIP_SKIP_SET_WAKE,
+	.flags			= IRQCHIP_SKIP_SET_WAKE |
+				  IRQCHIP_CAN_DELIVER_AS_NMI,
 };
 
 static inline void init_IO_APIC_traps(void)
-- 
2.7.4