[dpdk-dev] [PATCH] bus/pci: fix unexpected resource mapping override

Zhang, Qi Z qi.z.zhang at intel.com
Wed Oct 3 15:03:34 CEST 2018

> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas at monjalon.net]
> Sent: Sunday, September 30, 2018 4:53 PM
> To: Zhang, Qi Z <qi.z.zhang at intel.com>
> Cc: dev at dpdk.org; Burakov, Anatoly <anatoly.burakov at intel.com>; Yigit,
> Ferruh <ferruh.yigit at intel.com>; geoffrey.lv at gmail.com;
> ajit.khaparde at broadcom.com; stable at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] bus/pci: fix unexpected resource mapping
> override
> 29/09/2018 08:43, Zhang, Qi Z:
> > From: Thomas Monjalon [mailto:thomas at monjalon.net]
> > >
> > > Hi,
> > >
> > > 03/09/2018 10:40, Qi Zhang:
> > > > When scanning an already plugged device, the virtual address of
> > > > mapped PCI resource in rte_pci_device will be overridden with 0,
> > > > that may cause driver does not work correctly.
> > >
> > > Why is it overridden with 0?
> > > Can we try to fix the root cause?
> >
> > From my view this is place to fix the issue: "scan an already probed device
> will corrupt the PCI resource map"
> > Another option is "to prevent scan an already probed device", this can be
> implemented by adding some check before bus->scan in rte_dev_hotplug_add
> but I'm not prefer for this solution, because it's better to keep bus->scan's
> independency.
> I don't understand why we are currently changing an already scanned device in
> pci_scan_one.

OK, this need to be figured out, due to hotplug, bus scan is unpredictable, so between two scans, something could happen
device maybe be unbound then bound with a different driver, or vf number is changed, so device information need to be updated.
but I'm not sure if resource mapping address ( read from /sys/bus/pci/devices/<pci addr>/resource) is possible be changed or not. 
Though I don't have evidence that it is possible, but the patch respect the original assumption that it is possible, so I keep memmove here.
But I will not be surprise if It should be removed and the assumption is not correct.  

> We could check the PCI address is known at the beginning and stop here, even
> before allocating a new rte_pci_device.

Yes we could check this at beginning, which means we need to figure out the rte_device by a pci address , then call rte_dev_is_probed(dev), I think that require another iterate on rte_pci_bus->device_list.
So, the benefit of a lazy check is we could merge this iterate with the iterate for device information update, and I don't have strong option for both options

> Why trying to override with this memmove?

comment in my first segment.

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