linux-kernel - Re: [PATCH v1 02/14] iommufd: Add nesting related data structures for ARM SMMUv3

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Message-ID: <20230310125453.GB1745536@myrica>
Date:   Fri, 10 Mar 2023 12:54:53 +0000
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Nicolin Chen <nicolinc@...dia.com>
Cc:     Jason Gunthorpe <jgg@...dia.com>, robin.murphy@....com,
        will@...nel.org, eric.auger@...hat.com, kevin.tian@...el.com,
        baolu.lu@...ux.intel.com, joro@...tes.org,
        shameerali.kolothum.thodi@...wei.com,
        linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, yi.l.liu@...el.com
Subject: Re: [PATCH v1 02/14] iommufd: Add nesting related data structures
 for ARM SMMUv3

On Thu, Mar 09, 2023 at 08:50:52PM -0800, Nicolin Chen wrote:
> On Thu, Mar 09, 2023 at 10:48:50AM -0400, Jason Gunthorpe wrote:
> 
> > Nicolin, I think we should tweak the uAPI here so that the
> > invalidation opaque data has a format tagged on its own, instead of
> > re-using the HWPT tag. Ie you can have a ARM SMMUv3 invalidate type
> > tag and also a virtio-viommu invalidate type tag.
> 
> The invalidation tage is shared with the hwpt allocation. Does
> it mean that virtio-iommu won't have it's own allocation tag?

I'm not entirely sure what you mean by allocation tag. For example with
SMMU, when attaching page tables (SMMUv2), the guest passes an ASID at
allocation, and when it modifies that address space it passes the same
ASID for invalidation. When attaching PASID tables (SMMUv3), it writes the
ASID/PASID in the PASID table, and passes both in the invalidation.

Note that none of this is set in stone. It copies the Linux API we
originally discussed, but we were waiting for progress on that front
before committing to anything. Now we'll probably align to the new API
where possible, leaving out what doesn't work for virtio-iommu.

Thanks,
Jean