On 2024/11/16 08:34, Jason Gunthorpe wrote:
On Fri, Nov 15, 2024 at 02:07:41PM -0800, Nicolin Chen wrote:
On Thu, Nov 14, 2024 at 12:20:10PM -0400, Jason Gunthorpe wrote:
On Wed, Nov 13, 2024 at 07:18:42PM -0800, Nicolin Chen wrote:
so the user would try to create vDevices with a given viommu_obj until
failure, then it would allocate another viommu_obj for the failed device.
is it? sounds reasonable.
Yes. It is the same as previously dealing with a nesting parent:
test and allocate if fails. The virtual IOMMU driver in VMM can
keep a list of the vIOMMU objects for each device to test.
The viommu object should be tied to the VMM's vIOMMU vHW object that
it is paravirtualizing toward the VM.
So we shouldn't be creating viommu objects on demand, it should be
created when the vIOMMU is created, and the presumably the qemu
command line will describe how to link vPCI/VFIO functions to vIOMMU
instances. If they kernel won't allow the user's configuration then it
should fail, IMHO.
Intel's virtual IOMMU in QEMU has one instance but could create
two vIOMMU objects for devices behind two different pIOMMUs. So,
in this case, it does the on-demand (or try-and-fail) approach?
I suspect Intel does need viommu at all, and if it ever does it will
not be able to have one instance..
hmmm. As long as I got, the viommu_obj is a representative of the hw
IOMMU slice of resource used by the VM. It is hence instanced per hw
iommu. Based on this, one vIOMMU can have multiple or one viommu_obj.
Either should be allowed by design.
BTW. @Nic, I think the viommu_obj instance is not strictly be per hw
IOMMUs. e.g. two devices behind one hw IOMMU can have their own viommu_obj
as well. Is it? I didn't see a problem for it. So the viommu_obj is
instanced >= hw IOMMU number used by the VM.
Regards,
Yi Liu
