RE: [PATCH] iommu/vt-d: Add a fix for devices need extra dtlb flush

[Tian, Kevin]

> From: Robin Murphy <robin.murphy@xxxxxxx>
> Sent: Wednesday, November 23, 2022 1:49 AM
> 
> > +
> > +/* Impacted QAT device IDs ranging from 0x4940 to 0x4943 */
> > +#define BUGGY_QAT_DEVID_MASK 0x494c
> > +static bool dev_needs_extra_dtlb_flush(struct pci_dev *pdev)
> > +{
> > +	if (pdev->vendor != PCI_VENDOR_ID_INTEL)
> > +		return false;
> > +
> > +	if ((pdev->device & 0xfffc) != BUGGY_QAT_DEVID_MASK)
> > +		return false;
> > +
> > +	if (risky_device(pdev))
> > +		return false;
> 
> Hmm, I'm not sure that that makes much sense to me - what privilege can
> the device gain from being told to invalidate things twice? Why would we
> want to implicitly *allow* a device to potentially keep using a stale
> translation if for some bizarre reason firmware has marked it as
> external, surely that's worse?
> 

ATS is disabled for such device hence no dtlb at all.

bool pci_ats_supported(struct pci_dev *dev)
{
	if (!dev->ats_cap)
		return false;

	return (dev->untrusted == 0);
}

So above check doesn't make things worse. It's kind of meaningless
but according to Baolu he wants that check in every quirk...