On Thu, 25 Apr 2019 09:40:31 +0200 Auger Eric <[email protected]> wrote:
> Hi Liu, > > On 4/25/19 9:12 AM, Liu, Yi L wrote: > > Hi Eric, > > > >> From: Auger Eric [mailto:[email protected]] > >> Sent: Thursday, April 25, 2019 1:28 AM > >> To: Jacob Pan <[email protected]>; > >> [email protected]; 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 <[email protected]> > >>> > >>> 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." > > OK I understand. But strictly speaking a vIOMMU may not implement CM. > But that's nitpicking ;-) > CAP.CM (caching mode) and ECAP.VCS(virtual command support) are separate. I think we are mixing the two here since both are sufficient condition to indicate whether we are running in a guest. > Thanks > > Eric > > > > Thanks, > > Yi Liu > > [Jacob Pan] _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
