linux-kernel - Re: [PATCH] pci/iov: VFs are never multifunction

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Date:	Thu, 09 Jan 2014 14:58:28 -0700
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	sathya.perla@...lex.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	ajit.khaparde@...lex.com, Don Dutile <ddutile@...hat.com>,
	subbu.seetharaman@...lex.com, Myron Stowe <myron.stowe@...hat.com>
Subject: Re: [PATCH] pci/iov: VFs are never multifunction

On Thu, 2014-01-09 at 14:39 -0700, Bjorn Helgaas wrote:
> On Thu, Jan 9, 2014 at 11:25 AM, Alex Williamson
> <alex.williamson@...hat.com> wrote:
> > On Thu, 2014-01-09 at 11:08 -0700, Bjorn Helgaas wrote:
> >> On Thu, Jan 9, 2014 at 8:36 AM, Alex Williamson
> >> <alex.williamson@...hat.com> wrote:
> >> > Per the SR-IOV spec rev 1.1:
> >> >
> >> > 3.4.1.9 Header Type (Offset 0Eh)
> >> >
> >> > "... For VFs, this register must be RO Zero."
> >> >
> >> > Unfortunately some devices get this wrong, ex. Emulex OneConnect 10Gb
> >> > NIC.  When they do it makes us handle ACS testing and therefore IOMMU
> >> > groups as if they were actual multifunction devices and require ACS
> >> > capabilities to make sure there's no peer-to-peer between functions.
> >> > VFs are never traditional multifunction devices, so simply clear this
> >> > bit before we get any further into setup.
> >>
> >> This seems reasonable.  Do you have "lspci -vvxxxx" output for this
> >> device?  I'd like to save it for future reference.
> >
> > Sure, here's a VF:
> >
> > 09:04.0 Ethernet controller: Emulex Corporation OneConnect 10Gb NIC (be3) (rev 01)
> >         Subsystem: Emulex Corporation Device e722
> 
> Thanks!  I put this in
> https://bugzilla.kernel.org/show_bug.cgi?id=68431, and I'll add a
> reference to the changelog.
> 
> But I wonder if we can make this slightly more generic by doing
> something like this in pci_setup_device():
> 
>   dev->multifunction = (PCI_FUNC(dev->devfn) == 0) && (hdr_type & 0x80);
> 
> That's basically what lspci does in pci_generic_scan_bus(), and
> section 3.2.2.3.4 of the PCI 3.0 spec sort of implies that we should
> only look at the bit 7 of the header type for function 0:
> 
>   If a single function device is detected (i.e., bit 7 in the Header
>   Type register of function 0 is 0), no more functions for that
>   Device Number will be checked. If a multi-function device is
>   detected (i.e., bit 7 in the Header Type register of function 0
>   is 1), then all remaining Function Numbers will be checked.

We could do that and rely only on pci_scan_slot() to set multifunction=1
for the other functions, but that doesn't completely solve this problem.
VFs can occupy function zero and the example device would still set
multifunction with that test.  Thanks,

Alex

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