linux-kernel - Re: [PATCH] iommu: Relax ACS requirement for Intel RCiEP devices.

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Date:   Thu, 28 May 2020 09:33:15 -0700
From:   "Raj, Ashok" <ashok.raj@...el.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Darrel Goeddel <DGoeddel@...cepoint.com>,
        Mark Scott <mscott@...cepoint.com>,
        Romil Sharma <rsharma@...cepoint.com>,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCH] iommu: Relax ACS requirement for Intel RCiEP devices.

Hi Alex

On Tue, May 26, 2020 at 05:07:15PM -0600, Alex Williamson wrote:
> > ---
> >  drivers/iommu/iommu.c | 13 ++++++++++++-
> >  1 file changed, 12 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index 2b471419e26c..31b595dfedde 100644
> > --- a/drivers/iommu/iommu.c
> > +++ b/drivers/iommu/iommu.c
> > @@ -1187,7 +1187,18 @@ static struct iommu_group *get_pci_function_alias_group(struct pci_dev *pdev,
> >  	struct pci_dev *tmp = NULL;
> >  	struct iommu_group *group;
> >  
> > -	if (!pdev->multifunction || pci_acs_enabled(pdev, REQ_ACS_FLAGS))
> > +	/*
> > +	 * Intel VT-d Specification Section 3.16, Root-Complex Peer to Peer
> > +	 * Considerations manadate that all transactions in RCiEP's and
> > +	 * even Integrated MFD's *must* be sent up to the IOMMU. P2P is
> > +	 * only possible on translated addresses. This gives enough
> > +	 * guarantee that such devices can be forgiven for lack of ACS
> > +	 * support.
> > +	 */
> > +	if (!pdev->multifunction ||
> > +	    (pdev->vendor == PCI_VENDOR_ID_INTEL &&
> > +	     pci_pcie_type(pdev) == PCI_EXP_TYPE_RC_END) ||
> > +	     pci_acs_enabled(pdev, REQ_ACS_FLAGS))
> >  		return NULL;
> >  
> >  	for_each_pci_dev(tmp) {
> 
> Hi Ashok,
> 
> As this is an Intel/VT-d standard, not a PCIe standard, why not
> implement this in pci_dev_specific_acs_enabled() with all the other
> quirks?  Thanks,

Yes, that sounds like the right place.. I have a new patch, once its tested
i'll resend it. Thanks for pointing it out.

Cheers,
Ashok