linux-kernel - RE: [PATCH v1 14/14] iommu/arm-smmu-v3: Add arm_smmu_cache_invalidate

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Date:   Tue, 28 Mar 2023 03:03:11 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Nicolin Chen <nicolinc@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     Robin Murphy <robin.murphy@....com>,
        "will@...nel.org" <will@...nel.org>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v1 14/14] iommu/arm-smmu-v3: Add
 arm_smmu_cache_invalidate_user

> From: Nicolin Chen <nicolinc@...dia.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.