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

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Message-ID: <BN9PR11MB527620902046A4339EAACD3F8C0C9@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Wed, 23 Nov 2022 01:02:29 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Robin Murphy <robin.murphy@....com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>
CC:     Will Deacon <will@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Luo, Yuzhang" <yuzhang.luo@...el.com>
Subject: RE: [PATCH] iommu/vt-d: Add a fix for devices need extra dtlb flush

> From: Robin Murphy <robin.murphy@....com>
> 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...