Re: [net-next 5/5] PCI: disable FLR for 82579 device

[Jeff Kirsher <jeffrey.t.kirsher@intel.com>]

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On Fri, 2016-09-23 at 09:01 -0500, Bjorn Helgaas wrote:
> On Thu, Sep 22, 2016 at 11:39:01PM -0700, Jeff Kirsher wrote:
> > 
> > From: Sasha Neftin <sasha.neftin@intel.com>
> > 
> > 82579 has a problem reattaching itself after the device is detached.
> > The bug was reported by Redhat. The suggested fix is to disable
> > FLR capability in PCIe configuration space.
> > 
> > Reproduction:
> > Attach the device to a VM, then detach and try to attach again.
> > 
> > Fix:
> > Disable FLR capability to prevent the 82579 from hanging.
> 
> Is there a bugzilla or other reference URL to include here?  Should
> this be marked for stable?

So the author is in Israel, meaning it is their weekend now.  I do not
believe Sasha monitors email over the weekend, so a response to your
questions won't happen for a few days.

I tried searching my archives for more information, but had no luck finding
any additional information.

> > Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
> > Tested-by: Aaron Brown <aaron.f.brown@intel.com>
> > Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
> > ---
> >  drivers/pci/quirks.c | 21 +++++++++++++++++++++
> >  1 file changed, 21 insertions(+)
> > 
> > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > index 44e0ff3..59fba6e 100644
> > --- a/drivers/pci/quirks.c
> > +++ b/drivers/pci/quirks.c
> > @@ -4431,3 +4431,24 @@ static void quirk_intel_qat_vf_cap(struct
> > pci_dev *pdev)
> >  	}
> >  }
> >  DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x443,
> > quirk_intel_qat_vf_cap);
> > +/*
> > + * Workaround FLR issues for 82579
> > + * This code disables the FLR (Function Level Reset) via PCIe, in
> > order
> > + * to workaround a bug found while using device passthrough, where the
> > + * interface would become non-responsive.
> > + * NOTE: the FLR bit is Read/Write Once (RWO) in config space, so if
> > + * the BIOS or kernel writes this register * then this workaround will
> > + * not work.
> 
> This doesn't sound like a root cause.  Is the issue a hardware
> erratum?  Linux PCI core bug?  VFIO bug?  Device firmware bug?
> 
> The changelog suggests that the problem only affects passthrough,
> which suggests some sort of kernel bug related to how passthrough is
> implemented.
> 
> > 
> > + */
> > +static void quirk_intel_flr_cap_dis(struct pci_dev *dev)
> > +{
> > +	int pos = pci_find_capability(dev, PCI_CAP_ID_AF);
> > +	if (pos) {
> > +		u8 cap;
> > +		pci_read_config_byte(dev, pos + PCI_AF_CAP, &cap);
> > +		cap = cap & (~PCI_AF_CAP_FLR);
> > +		pci_write_config_byte(dev, pos + PCI_AF_CAP, cap);
> > +	}
> > +}
> > +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x1502,
> > quirk_intel_flr_cap_dis);
> > +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x1503,
> > quirk_intel_flr_cap_dis);
> > -- 
> > 2.7.4
> > 
> > --
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