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From:   "Tian, Kevin" <kevin.tian@intel.com>
To:     Jason Gunthorpe <jgg@nvidia.com>
CC:     Jacob Pan <jacob.jun.pan@linux.intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
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Subject: RE: [PATCH v7 3/4] iommu/vt-d: Add set_dev_pasid callback for dma
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Thread-Topic: [PATCH v7 3/4] iommu/vt-d: Add set_dev_pasid callback for dma
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Thread-Index: AQHZjZxI8RRUCSa7gUG6SDjy6Qi7Gq9qiM7ggAiOtACAFv0BcA==
Date:   Wed, 14 Jun 2023 08:13:49 +0000
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> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Wednesday, May 31, 2023 1:09 AM
>=20
>=20
> >  *   2) all SVA domains share a reserved domain id per recommendation
> >  *      from VT-d spec (section 6.2.3.1) so domain_detach_iommu() is
> >  *      not required;
>=20
> The DID should be managed and allocated for the S2 pointer and the
> flushing logic should work genericly by tracking the S2's being used
> and flushing their DIDs when all the S2s fall out of use. The special
> identity S2 just gets a static DID that never falls out of use.
>=20

I'm not sure it's worthwhile to fake a identity S2 for the bare metal
SVA case. It's far simpler to special case the reserved DID value in
the SVM path.