Re: [PATCH 0/2] PCI: Workaround for bus reset on Cavium cn8xxx root ports

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 23 May 2017 15:47:50 -0500
Bjorn Helgaas <helgaas@kernel.org> wrote:

> On Mon, May 15, 2017 at 05:17:34PM -0700, David Daney wrote:
> > With the recent improvements in arm64 and vfio-pci, we are seeing
> > failures like this (on cn8890 based systems):
> > 
> > [  235.622361] Unhandled fault: synchronous external abort (0x96000210) at 0xfffffc00c1000100
> > [  235.630625] Internal error: : 96000210 [#1] PREEMPT SMP
> > .
> > .
> > .
> > [  236.208820] [<fffffc0008411250>] pci_generic_config_read+0x38/0x9c
> > [  236.214992] [<fffffc0008435ed4>] thunder_pem_config_read+0x54/0x1e8
> > [  236.221250] [<fffffc0008411620>] pci_bus_read_config_dword+0x74/0xa0
> > [  236.227596] [<fffffc000841853c>] pci_find_next_ext_capability.part.15+0x40/0xb8
> > [  236.234896] [<fffffc0008419428>] pci_find_ext_capability+0x20/0x30
> > [  236.241068] [<fffffc0008423e2c>] pci_restore_vc_state+0x34/0x88
> > [  236.246979] [<fffffc000841af3c>] pci_restore_state.part.37+0x2c/0x1fc
> > [  236.253410] [<fffffc000841b174>] pci_dev_restore+0x4c/0x50
> > [  236.258887] [<fffffc000841b19c>] pci_bus_restore+0x24/0x4c
> > [  236.264362] [<fffffc000841c2dc>] pci_try_reset_bus+0x7c/0xa0
> > [  236.270021] [<fffffc00060a1ab0>] vfio_pci_ioctl+0xc34/0xc3c [vfio_pci]
> > [  236.276547] [<fffffc0005eb0410>] vfio_device_fops_unl_ioctl+0x20/0x30 [vfio]
> > [  236.283587] [<fffffc000824b314>] do_vfs_ioctl+0xac/0x744
> > [  236.288890] [<fffffc000824ba30>] SyS_ioctl+0x84/0x98
> > [  236.293846] [<fffffc0008082ca0>] __sys_trace_return+0x0/0x4
> > 
> > These are caused by the inability of the PCIe root port and Intel
> > e1000e to sucessfully do a bus reset.
> > 
> > The proposed fix is to not do a bus reset on these systems.
> > 
> > David Daney (2):
> >   PCI: Allow PCI_DEV_FLAGS_NO_BUS_RESET to be used on bus device.
> >   PCI: Avoid bus reset for Cavium cn8xxx root ports.
> > 
> >  drivers/pci/pci.c    | 4 ++++
> >  drivers/pci/quirks.c | 8 ++++++++
> >  2 files changed, 12 insertions(+)  
> 
> Applied with Eric's reviewed-by and typo fixes to pci/virtualization for
> v4.13, thanks!

Hmm, well let me again express my concerns that I'm really not sure how
to support this since it removes our last opportunity to reset devices
that may otherwise have no reset mechanism.  Certain classes of devices
are entirely unsupportable for the code path indicated above without a
bus reset.  If we have an endpoint device that goes bonkers at a bus
reset, at least we know it's going to behave just as poorly no matter
what the host platform.  This series allows endpoints that work
perfectly well on one host to be handled differently on another.  It
certainly suggests something non-spec compliant about the root port
implementation and I wish there was more analysis about exactly what
that problem is since this is coming from the hardware vendor.

https://lkml.org/lkml/2017/5/16/662

Thanks,
Alex