Hi,
On 10/22/18 6:22 PM, Raj, Ashok wrote:
On Mon, Oct 22, 2018 at 12:49:47PM +0800, Lu Baolu wrote:
Hi,
On 10/20/18 2:11 AM, Jean-Philippe Brucker wrote:
Some devices might support multiple DMA address spaces, in particular
those that have the PCI PASID feature. PASID (Process Address Space ID)
allows to share process address spaces with devices (SVA), partition a
device into VM-assignable entities (VFIO mdev) or simply provide
multiple DMA address space to kernel drivers. Add a global PASID
allocator usable by different drivers at the same time. Name it I/O ASID
to avoid confusion with ASIDs allocated by arch code, which are usually
a separate ID space.
The IOASID space is global. Each device can have its own PASID space,
but by convention the IOMMU ended up having a global PASID space, so
that with SVA, each mm_struct is associated to a single PASID.
The allocator doesn't really belong in drivers/iommu because some
drivers would like to allocate PASIDs for devices that aren't managed by
an IOMMU, using the same ID space as IOMMU. It doesn't really belong in
drivers/pci either since platform device also support PASID. Add the
allocator in drivers/base.
One concern of moving pasid allocator here is about paravirtual
allocation of pasid.
Since there is only a single set of pasid tables which is controlled by
Minor correction: Single system wide PASID namespace, but PASID tables
would be created ideally per-bdf for isolation purposes.
I'm sure you meant name space, but didn't want that to be mis-interpreted.
Yes, confirmed.
Best regards,
Lu Baolu
the host, the pasid is a system wide resource. When a driver running in
a guest VM wants to consume a pasid, it must be intercepted by the
simulation software and routed the allocation to the host via VFIO. Some
iommu arch's provide mechanisms to aid this, for example, the virtual
command interfaces defined in vt-d 3.0. Any pasid used in guest VM
should go through the virtual command interfaces.
Cheers,
Ashok
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