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

Auger Eric
2019-04-25T07:40:39Z

Hi Liu,

On 4/25/19 9:12 AM, Liu, Yi L wrote:
> 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."

OK I understand. But strictly speaking a vIOMMU may not implement CM.
But that's nitpicking ;-)

Thanks

Eric
>
> Thanks,
> Yi Liu
>