RE: [PATCH v2 09/19] iommu/vt-d: Enlightened PASID allocation

[Liu, Yi L]

Hi Eric,

> From: Auger Eric [mailto:eric.auger@xxxxxxxxxx]
> Sent: Thursday, April 25, 2019 1:28 AM
> To: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx;
> 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@xxxxxxxxxxxxxxx>
> >
> > 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