Hi Joerg,
On 11/8/18 12:43 AM, [email protected] wrote:
Hi,
On Wed, Nov 07, 2018 at 11:40:30AM +0800, Lu Baolu wrote:
Hi Joerg,
On 11/7/18 12:25 AM, [email protected] wrote:
Nowadays, we can find PASID granular DMA translation on both ARM and x86
platforms. With PASID granular DMA translation supported in system iommu, if
a device divides itself into multiple subsets and tag the DMA
transfers of each subset with a unique PASID, each subset become
assignable. We call the assignable subset as an ADI (Assignable Device
Interface). As the result, each ADI could be attached with a domain.
Yeah, I know the background. The point is, the IOMMU-API as of today
implements a strict one-to-one relationship between domains and devices,
every device can only have one domain assigned at a given time. If we
assign a new domain to a device, the old gets unassigned.
If we allow to attach multiple domains to a single device we
fundamentally break that semantic.
Yes. In the latest v4 submission, we use the aux-domain specific APIs to
attach/detach the domain to a device. Do you see other APIs that will
possibly break this semantic?
Therefore I think it is better is support the ADI devices with
subdomains and a new set of functions in the API to handle only these
sub-domains.
Can you please elaborate a bit more about the concept of subdomains?
From my point of view, an aux-domain is a normal un-managed domain which
has a PASID and could be attached to any ADIs through the aux-domain
specific attach/detach APIs. It could also be attached to a device with
the existing domain_attach/detach_device() APIs at the same time, hence
mdev and pci devices in a vfio container could share a domain.
Best regards,
Lu Baolu
Further more, a single domain might be attached to an ADI of device A,
while attached to another legacy device B which doesn't support PASID
features. In this case, we say "Domain 4" is attached to ADI(PASID#x) in
aux mode and attached to device B in primary mode.
This will of course not work with subdomains, but is that really
necessary? VFIO already allocates a separate domain for each device
anyway (iirc), so it is unlikely that is uses the same domain for a
legacy and an ADI device.
Regards,
Joerg
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