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SubjectRe: [PATCH v3 5/6] iommu/vt-d: Flush PASID-based iotlb for iova over first level
Hi Yi,

On 12/15/19 5:22 PM, Liu, Yi L wrote:
> Ok, let me explain more... default pasid is meaningful only when
> the domain has been attached to a device as an aux-domain. right?

No exactly. Each domain has a specific default pasid, no matter normal
domain (RID based) or aux-domain (PASID based). The difference is for a
normal domain RID2PASID value is used, for an aux-domain the pasid is
allocated from a global pool.

The same concept used in VT-d 3.x scalable mode. For RID based DMA
translation RID2PASID value is used when walking the tables; For PASID
based DMA translation a real pasid in the transaction is used.

> If a domain only has one device, and it is attached to this device as
> normal domain (normal domain means non aux-domain here). Then
> you should flush cache with domain-id and RID2PASID value.
> If a domain has one device, and it is attached to this device as
> aux-domain. Then you may want to flush cache with domain-id
> and default pasid. right?

A domain's counterpart is IOMMU group. So we say attach/detach domain
to/from devices in a group. We don't allow devices with different
default pasid sitting in a same group, right?

> Then let's come to the case I mentioned in previous email. a mdev
> and another device assigned to a single VM. In host, you will have
> a domain which has two devices, one device(deva) is attached as

No. We will have two IOMMU groups and two domains. Correct me if my
understanding is not right.

Best regards,

> normal domain, another one (devB) is attached as aux-domain. Then
> which pasid should be used when the mapping in IOVA page table is
> modified? RID2PASID or default pasid? I think both should be used
> since the domain means differently to the two devices. If you just
> use default pasid, then deva may still be able to use stale caches.
> Regards,
> Yi Liu

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