Public bug reported:
Description
To support live migration of mediated device assignment with SVM/SVA, guest
must have its own PASID namespace.
Our first implementation of SVM uses system wide PASID allocation scheme which
is not live migration friendly.
Proposed by Kevin Tian and Yi Liu from virtualization team, we need to add
extensions to IOMMU guest SVA bind APIs. The work flow is as follows:
Here is a flow if QEMU chooses to do non-identity mapping of G-H PASID.
1. Guest does sva_bind_mm()
2. Guest calls vcmd, qemu returns guest PASID, allocate host pasid from
host IOMMU driver, QEMU maintains G->H PASID lookup.
3. Guest IOMMU driver programs GPASID entry, then do PASID cache invalidate
4. QEMU traps PASID cache flush, find matching host PASID with mapping
from #2
5. Host IOMMU driver does bind_gpasid(hpasid, gpasid, dev), maintains H->G
PASID lookup in host IOMMU driver
6. Guest programs mdev DWQ with GPASID, trapped in QEMU then VDCM
7. VDCM calls the newly proposed iommu_get_hpasid() API to do G->H lookup
established in #5 (reverse), then program hpasid in HW.
PRQ:
1. Host IOMMU receives PRQ with hpasid
2. Host IOMMU looks up guest PASID (which is in private data as part of
the gpasid bind), Reports PRQ fault with host PASID with guest PASID as private
data(avoid reverse lookup in QEMU on performance path)
3. QEMU receives PRQ with host PASID, obtain guest PASID from fault
private data
PR response
1. Guest send page response with guest PASID
2. QEMU does G->H PASID look up
3. QEMU passdown page response with host PASID
Note:
- Fast lookup directions
- QEMU does G->H lookup
- IOMMU driver does H->G lookup
- Reverse lookup
- IOMMU driver does G->H reverse look up only for slow path
Target Release: 20.10
Target Kernel: 5.9
** Affects: intel
Importance: Undecided
Status: New
** Affects: ubuntu
Importance: Undecided
Status: New
** Tags: intel-kernel-20.10
** Also affects: ubuntu
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1878514
Title:
[IOMMU] Support guest host PASID non-identity mapping
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