[RFC PATCH v2 43/45] arm64: smp: Add NMI support for LPI-backed IPIs

[Vladimir Murzin]

LPI-backed IPIs are currently always requested and managed as regular
IRQs. Allow IPIs selected by ipi_should_be_nmi() to be requested as
NMIs, falling back to regular IRQs when the NMI request fails.

Track which IPIs were successfully requested as NMIs so that the
per-CPU enable and disable paths use the appropriate NMI helpers.

Signed-off-by: Vladimir Murzin <vladimir.murzin at arm.com>
---
 arch/arm64/kernel/smp.c | 34 +++++++++++++++++++++++++++++-----
 1 file changed, 29 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 9bacdbb2aa44..012633ea8347 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -1123,16 +1123,24 @@ static const struct ipi_irq_ops ipi_sgi_ops = {
 
 static void ipi_lpi_enable(int cpu, int ipi)
 {
-	enable_irq(irq_desc_get_irq(get_ipi_desc(cpu, ipi)));
+	if (test_bit(ipi, get_ipi_nmi_bitmap(cpu)))
+		enable_nmi(irq_desc_get_irq(get_ipi_desc(cpu, ipi)));
+	else
+		enable_irq(irq_desc_get_irq(get_ipi_desc(cpu, ipi)));
 }
 
 static void ipi_lpi_disable(int cpu, int ipi)
 {
-	disable_irq(irq_desc_get_irq(get_ipi_desc(cpu, ipi)));
+	if (test_bit(ipi, get_ipi_nmi_bitmap(cpu)))
+		disable_nmi_nosync(irq_desc_get_irq(get_ipi_desc(cpu, ipi)));
+	else
+		disable_irq(irq_desc_get_irq(get_ipi_desc(cpu, ipi)));
 }
 
 static void ipi_lpi_setup(int ipi, int ncpus)
 {
+	bool is_nmi = ipi_should_be_nmi(ipi);
+
 	for (int cpu = 0; cpu < ncpus; cpu++) {
 		int err, irq;
 
@@ -1141,13 +1149,29 @@ static void ipi_lpi_setup(int ipi, int ncpus)
 		err = irq_force_affinity(irq, cpumask_of(cpu));
 		WARN(err, "Could not force affinity IRQ %d, err=%d\n", irq, err);
 
-		err = request_irq(irq, ipi_handler, IRQF_NO_AUTOEN, "IPI",
-				  NULL);
-		WARN(err, "Could not request IRQ %d, err=%d\n", irq, err);
+		/*
+		 * Try to request NMI if it should be
+		 */
+		if (is_nmi && request_nmi(irq, ipi_handler, IRQF_PERCPU | IRQF_NO_AUTOEN, "IPI", NULL)) {
+			/*
+			 * Fallback to regular IRQ
+			 */
+			is_nmi = false;
+		}
+		/*
+		 * Otherwise regular IRQ
+		 */
+		if (!is_nmi) {
+			err = request_irq(irq, ipi_handler, IRQF_NO_AUTOEN, "IPI", NULL);
+			WARN(err, "Could not request IRQ %d, err=%d\n", irq, err);
+		}
 
 		irq_set_status_flags(irq, (IRQ_HIDDEN | IRQ_NO_BALANCING_MASK));
 
 		get_ipi_desc(cpu, ipi) = irq_to_desc(irq);
+
+		if (is_nmi)
+			set_bit(ipi, get_ipi_nmi_bitmap(cpu));
 	}
 }
 
-- 
2.34.1