On 2023/12/12 23:35, Jason Gunthorpe wrote:
On Mon, Dec 11, 2023 at 11:49:49AM -0700, Alex Williamson wrote:
On Mon, 11 Dec 2023 14:10:28 -0400
Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:
On Mon, Dec 11, 2023 at 11:03:45AM -0700, Alex Williamson wrote:
On Sun, 26 Nov 2023 22:39:09 -0800
Yi Liu <yi.l.liu@xxxxxxxxx> wrote:
the PF). Creating a virtual PASID capability in vfio-pci config space needs
to find a hole to place it, but doing so may require device specific
knowledge to avoid potential conflict with device specific registers like
hiden bits in VF config space. It's simpler by moving this burden to the
VMM instead of maintaining a quirk system in the kernel.
This feels a bit like an incomplete solution though and we might
already posses device specific knowledge in the form of a variant
driver. Should this feature structure include a flag + field that
could serve to generically indicate to the VMM a location for
implementing the PASID capability? The default core implementation
might fill this only for PFs where clearly an emualted PASID capability
can overlap the physical capability. Thanks,
In many ways I would perfer to solve this for good by having a way to
learn a range of available config space - I liked the suggestion to
use a DVSEC to mark empty space.
Yes, DVSEC is the most plausible option for the device itself to convey
unused config space, but that requires hardware adoption so presumably
we're going to need to fill the gaps with device specific code. That
code might live in a variant driver or in the VMM. If we have faith
that DVSEC is the way, it'd make sense for a variant driver to
implement a virtual DVSEC to work out the QEMU implementation and set a
precedent.
How hard do you think it would be for the kernel to synthesize the
dvsec if the varient driver can provide a range for it?
On the other hand I'm not so keen on having variant drivers that are
only doing this just to avoid a table in qemu :\ It seems like a
reasonable thing to add to existing drivers, though none of them
support PASID yet..
I mostly just want us to recognize that this feature structure also has
the possibility to fill this gap and we're consciously passing it over
and should maybe formally propose the DVSEC solution and reference it
in the commit log or comments here to provide a complete picture.
You mean by passing an explicit empty range or something in a feature
IOCTL?
Hi Alex,
Any more suggestion on this? It appears to me that you are fine with PF
to implement the virtual PASID capability in the same offset with physical
PASID capability, while other cases need a way to know where to put the
virtual PASID capability. This may be done by a DVSEC or just pass empty
ranges through the VFIO_DEVICE_FEATURE ioctl?
Regards,
Yi Liu
