Messages in this thread | | | From | "Liu, Yi L" <> | Subject | RE: [PATCH v2 09/19] iommu/vt-d: Enlightened PASID allocation | Date | Thu, 25 Apr 2019 07:12:02 +0000 |
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Hi Eric,
> From: Auger Eric [mailto:eric.auger@redhat.com] > Sent: Thursday, April 25, 2019 1:28 AM > To: Jacob Pan <jacob.jun.pan@linux.intel.com>; iommu@lists.linux-foundation.org; > Subject: Re: [PATCH v2 09/19] iommu/vt-d: Enlightened PASID allocation > > Hi Jacob, > > On 4/24/19 1:31 AM, Jacob Pan wrote: > > From: Lu Baolu <baolu.lu@linux.intel.com> > > > > If Intel IOMMU runs in caching mode, a.k.a. virtual IOMMU, the IOMMU > > driver should rely on the emulation software to allocate and free > > PASID IDs. > Do we make the decision depending on the CM or depending on the VCCAP_REG? > > VCCAP_REG description says: > > If Set, software must use Virtual Command Register interface to allocate and free > PASIDs.
The answer is it depends on the ECAP.VCS and then the PASID allocation bit in VCCAP_REG. But VCS bit implies the iommu is a software implementation (vIOMMU) of vt-d architecture. Pls refer to the descriptions of "Virtual Command Support" in vt-d 3.0 spec.
"Hardware implementations of this architecture report a value of 0 in this field. Software implementations (emulation) of this architecture may report VCS=1."
Thanks, Yi Liu
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