On Fri, Jan 10, 2025 at 10:38:42AM -0800, Nicolin Chen wrote:

quoted

The virtual event queue should behave the same as if the physical
event queue overflows, and that logic should be in the smmu driver -
this should return some Exxx to indicate the queue is filled.

Hmm, the driver only screams...

static irqreturn_t arm_smmu_evtq_thread(int irq, void *dev)
{
[...]
		/*
		 * Not much we can do on overflow, so scream and pretend we're
		 * trying harder.
		 */
		if (queue_sync_prod_in(q) == -EOVERFLOW)
			dev_err(smmu->dev, "EVTQ overflow detected -- events lost\n");

Well it must know from the HW somehow that the overflow has happened??

quoted

I supposed we will need a way to indicate lost events to userspace on
top of this?

Perhaps another u32 flag in the arm_smmuv3_vevent struct to report
an overflow. That said, what userspace/VMM will need to do with it?

Trigger the above code in the VM somehow?

Jason