[Xen-devel] [PATCH] xen/arm: gic-v3: Make sure read from ICC_IAR1_EL1 is visible on the redistributor

[Julien Grall <julien.grall@xxxxxxx>]

From the GICv3 spec (IHI069C) section 4.1.1:
"The effects of reading ICC_IAR0_EL1 and ICC_IAR1_EL1 on the state of a
returned INTID are not guaranteed to be visible until after the execution
of a DSB".

Because of the GIC is an external component, a dsb sy is required.
Without it the sysreg read may not have been made visible on the
redistributor.

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

---

This patch should be backported up to Xen 4.6.
---
 xen/arch/arm/gic-v3.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/gic-v3.c b/xen/arch/arm/gic-v3.c
index 57ed9d9..955591b 100644
--- a/xen/arch/arm/gic-v3.c
+++ b/xen/arch/arm/gic-v3.c
@@ -459,7 +459,11 @@ static void gicv3_dir_irq(struct irq_desc *irqd)
 
 static unsigned int gicv3_read_irq(void)
 {
-    return READ_SYSREG32(ICC_IAR1_EL1);
+    unsigned int irq = READ_SYSREG32(ICC_IAR1_EL1);
+
+    dsb(sy);
+
+    return irq;
 }
 
 static inline uint64_t gicv3_mpidr_to_affinity(int cpu)
-- 
1.9.1


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