[PATCH 1/3] irqchip/gic-v3: ensure pseudo-NMIs have an ISB between ack and handling

[Mark Rutland]

There are cases where a context synchronization event is necessary
between an IRQ being raised and being handled, and there are races such
that we cannot rely upon the exception entry being subsequent to the
interrupt being raised.

We identified and fixes this for regular IRQs in commit:

  39a06b67c2c1256b ("irqchip/gic: Ensure we have an ISB between ack and ->handle_irq")

Unfortunately, we forgot to do the same for psuedo-NMIs when support for
those was added in commit:

  f32c926651dcd168 ("irqchip/gic-v3: Handle pseudo-NMIs")

Which means that when pseudo-NMIs are used for PMU support, we'll hit
the same problem.

Apply the same fix as for regular IRQs. Note that when EOI mode 1 is in
use, the call to gic_write_eoir() will provide an ISB.

Fixes: f32c926651dcd168 ("irqchip/gic-v3: Handle pseudo-NMIs")
Signed-off-by: Mark Rutland <mark.rutland at arm.com>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Will Deacon <will.deacon at arm.com>
---
 drivers/irqchip/irq-gic-v3.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index b252d5534547c..7305d84f2df5a 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -654,6 +654,9 @@ static inline void gic_handle_nmi(u32 irqnr, struct pt_regs *regs)
 
 	if (static_branch_likely(&supports_deactivate_key))
 		gic_write_eoir(irqnr);
+	else
+		isb()
+
 	/*
 	 * Leave the PSR.I bit set to prevent other NMIs to be
 	 * received while handling this one.
-- 
2.30.2