Subject: [PATCH] KVM: arm64: vgic: Read HW interrupt pending state from the HW

From: Marc Zyngier <[email-masked]>
Date: Tue, 8 Feb 2022 12:37:26 +0000

It appears that a read access to GIC[DR]_I[CS]PENDRn doesn't always
result in the pending interrupts being accurately reported if they are
mapped to a HW interrupt. This is particularily visible when acking
the timer interrupt and reading the GICR_ISPENDR1 register immediately
after, for example (the interrupt appears as not-pending while it really
is...).

This is because a HW interrupt has its 'active and pending state' kept
in the *physical* distributor, and not in the virtual one, as mandated
by the spec (this is what allows the direct deactivation). The virtual
distributor only caries the pending and active *states* (note the
plural, as these are two independent and non-overlapping states).

Fix it by reading the HW state back, either from the timer itself or
from the distributor if necessary.

Reported-by: Ricardo Koller <[email-masked]>
Signed-off-by: Marc Zyngier <[email-masked]>
---
 arch/arm64/kvm/vgic/vgic-mmio.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/kvm/vgic/vgic-mmio.c b/arch/arm64/kvm/vgic/vgic-mmio.c
index 7068da080799..49837d3a3ef5 100644
--- a/arch/arm64/kvm/vgic/vgic-mmio.c
+++ b/arch/arm64/kvm/vgic/vgic-mmio.c
@@ -248,6 +248,8 @@ unsigned long vgic_mmio_read_pending(struct kvm_vcpu *vcpu,
 						    IRQCHIP_STATE_PENDING,
 						    &val);
 			WARN_RATELIMIT(err, "IRQ %d", irq->host_irq);
+		} else if (vgic_irq_is_mapped_level(irq)) {
+			val = vgic_get_phys_line_level(irq);
 		} else {
 			val = irq_is_pending(irq);
 		}
-- 
2.34.1

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