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

From: "Raj, Ashok" <ashok.raj@intel.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: linux-pci@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
	Joerg Roedel <joro@8bytes.org>,
	linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Darrel Goeddel <DGoeddel@forcepoint.com>,
	Mark Scott <mscott@forcepoint.com>,
	Romil Sharma <rsharma@forcepoint.com>,
	Ashok Raj <ashok.raj@intel.com>
Subject: Re: [PATCH] iommu: Relax ACS requirement for Intel RCiEP devices.
Date: Thu, 28 May 2020 09:33:15 -0700	[thread overview]
Message-ID: <20200528163315.GA6461@otc-nc-03> (raw)
In-Reply-To: <20200526170715.18c0ee98@x1.home>

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