Re: [PATCH v7 07/10] iommufd: Fault-capable hwpt attach/detach/replace

[Baolu Lu]

On 2024/6/29 5:17, Jason Gunthorpe wrote:
> On Sun, Jun 16, 2024 at 02:11:52PM +0800, Lu Baolu wrote:
> > +static int iommufd_fault_iopf_enable(struct iommufd_device *idev)
> > +{
> > +	struct device *dev = idev->dev;
> > +	int ret;
> > +
> > +	/*
> > +	 * Once we turn on PCI/PRI support for VF, the response failure code
> > +	 * should not be forwarded to the hardware due to PRI being a shared
> > +	 * resource between PF and VFs. There is no coordination for this
> > +	 * shared capability. This waits for a vPRI reset to recover.
> > +	 */
> > +	if (dev_is_pci(dev) && to_pci_dev(dev)->is_virtfn)
> > +		return -EINVAL;
> I don't quite get this remark, isn't not supporting PRI on VFs kind of
> useless? What is the story here?

This remark is trying to explain why attaching an iopf-capable hwpt to a
VF is not supported for now. The PCI sepc (section 10.4.2.1) states that
a response failure will disable the PRI on the function. But for PF/VF
case, the PRI is a shared resource, therefore a response failure on a VF
might cause iopf on other VFs to malfunction. So, we start from simple
by not allowing it.

Best regards,
baolu