[PATCH v1 14/14] iommu/arm-smmu-v3: Add arm_smmu_cache_invalidate_user

[Tian, Kevin]

> From: Nicolin Chen <nicolinc at nvidia.com>
> Sent: Saturday, March 25, 2023 1:35 AM
> 
> On Fri, Mar 24, 2023 at 11:57:09AM -0300, Jason Gunthorpe wrote:
> >
> > If you suggest to overlay the main cmdq with the vcmdq and then don't
> > tell the guest about it.. Robin suggested something similar.

yes, that's my point.

> 
> Yea, I remember that too, from the email that I received from
> Robin on Christmas Eve :)
> 
> Yet, I haven't got a chance to run some experiment with that.
> 
> > This idea would be a half and half, the HW would run the queue and the
> > doorbell and generate error interrupts back to the hypervisor and tell
> > it that the queue is paused and ask it to fix the failed entry and
> > restart.
> >
> > I could see this as an interesting solution, but I don't know if this
> > HW can support it..
> 
> It possibly can, since an unsupported command will trigger an
> Illegal Command interrupt, then the IRQ handler could read it
> out of the CMDQ. Again, I'd need to run some experiment, once
> this SMMU nesting series is settled down to certain level.
> 

also you want to ensure that error is a recoverable type so
once sw fixes it the hw can continue to behave correctly.