On Fri, 12 Mar 2021 10:48:29 +0000,
Shenming Lu [off-list ref] wrote:

On 2021/3/12 17:05, Marc Zyngier wrote:

quoted

On Thu, 11 Mar 2021 12:32:07 +0000,
Shenming Lu [off-list ref] wrote:

quoted

On 2021/3/11 17:14, Marc Zyngier wrote:

quoted

On Wed, 27 Jan 2021 12:13:36 +0000,
Shenming Lu [off-list ref] wrote:

quoted

From: Zenghui Yu <yuzenghui@huawei.com>

When setting the forwarding path of a VLPI (switch to the HW mode),
we could also transfer the pending state from irq->pending_latch to
VPT (especially in migration, the pending states of VLPIs are restored
into kvm’s vgic first). And we currently send "INT+VSYNC" to trigger
a VLPI to pending.

Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Shenming Lu <redacted>
---
 arch/arm64/kvm/vgic/vgic-v4.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/arm64/kvm/vgic/vgic-v4.c b/arch/arm64/kvm/vgic/vgic-v4.c
index ac029ba3d337..a3542af6f04a 100644
--- a/arch/arm64/kvm/vgic/vgic-v4.c
+++ b/arch/arm64/kvm/vgic/vgic-v4.c

@@ -449,6 +449,20 @@ int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int virq,
 	irq->host_irq	= virq;
 	atomic_inc(&map.vpe->vlpi_count);
 
+	/* Transfer pending state */
+	if (irq->pending_latch) {
+		ret = irq_set_irqchip_state(irq->host_irq,
+					    IRQCHIP_STATE_PENDING,
+					    irq->pending_latch);
+		WARN_RATELIMIT(ret, "IRQ %d", irq->host_irq);
+
+		/*
+		 * Let it be pruned from ap_list later and don't bother
+		 * the List Register.
+		 */
+		irq->pending_latch = false;

NAK. If the interrupt is on the AP list, it must be pruned from it
*immediately*. The only case where it can be !pending and still on the
AP list is in interval between sync and prune. If we start messing
with this, we can't reason about the state of this list anymore.

Consider calling vgic_queue_irq_unlock() here.

Thanks for giving a hint, but it seems that vgic_queue_irq_unlock() only
queues an IRQ after checking, did you mean vgic_prune_ap_list() instead?

No, I really mean vgic_queue_irq_unlock(). It can be used to remove
the pending state from an interrupt, and drop it from the AP
list. This is exactly what happens when clearing the pending state of
a level interrupt, for example.

Hi, I have gone through vgic_queue_irq_unlock more than once, but
still can't find the place in it to drop an IRQ from the AP
list... Did I miss something ?...  Or could you help to point it
out? Thanks very much for this!

NO, you are right. I think this is a missing optimisation. Please call
the function anyway, as that's what is required to communicate a
change of state in general.

I'll have a think about it.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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