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SubjectRe: [PATCH] PCI: quirk for preventing bus reset on TI C667X
On Tue, Jan 26, 2021 at 01:22:18PM +0200, Antti Järvinen wrote:
> On 22.1.2021 1.55, Bjorn Helgaas wrote:>
>
> > It looks like we would probably be trying a Secondary Bus Reset using
> > the bridge leading to the C667X. Can you confirm?
>
> Yes, this is my understanding too.
>
> > Wonder if you
> > could try doing what pci_reset_secondary_bus() does by hand:
> >
>
> I tried this by hand. It looks that result is same as through VFIO.
>
> # cat sbr.sh
> BRIDGE=10:00.0
> C667X=11:00.0
>
> setpci -s$C667X VENDOR_ID.w
>
> VAL=$(setpci -s$BRIDGE BRIDGE_CONTROL.w)
> echo $VAL
> setpci -s$BRIDGE BRIDGE_CONTROL.w=$(($VAL | 0x40))
> sleep 1
> setpci -s$BRIDGE BRIDGE_CONTROL.w=$VAL
> sleep 1
> setpci -s$C667X VENDOR_ID.w=0
> setpci -s$C667X VENDOR_ID.w
>
>
> # ./sbr.sh
> 104c
> 0003
> ffff
>
>
> > # BRIDGE=... # PCI address, e.g., 00:1c.0
> > # C667X=...
> > # setpci -s$C667X VENDOR_ID.w
> > # setpci -s$BRIDGE BRIDGE_CONTROL.w # prints "val"
> > # setpci -s$BRIDGE BRIDGE_CONTROL.w= # val | 0x40 (set SBR)
> > # sleep 1
> > # setpci -s$BRIDGE BRIDGE_CONTROL.w= # val (clear SBR)
> > # sleep 1
> > # setpci -s$C667X VENDOR_ID.w=0
> > # setpci -s$C667X VENDOR_ID.w
> >
> > If we use this quirk and avoid the reset, I assume that means
> > assigning the device to VMs with VFIO will leak state between VMs?
>
> I think this is true.

Alex, is there some warning about situations like this where a device
may leak state between VMs?

There's nothing in quirk_no_bus_reset() itself where we set
PCI_DEV_FLAGS_NO_BUS_RESET, and nothing in pci_parent_bus_reset() or
pci_dev_reset_slot_function() where we test it, but I didn't chase
into VFIO.

Seems important enough that we might want to mention it at least once
and maybe even every time we try to reset the device. I hope the leak
isn't completely silent.

Bjorn

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