Messages in this thread | | | From | Haiyang Zhang <> | Subject | RE: [PATCH v4,1/2] PCI: hv: Detect and fix Hyper-V PCI domain number collision | Date | Wed, 14 Aug 2019 15:32:34 +0000 |
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> -----Original Message----- > From: Bjorn Helgaas <helgaas@kernel.org> > Sent: Wednesday, August 14, 2019 12:34 AM > To: Haiyang Zhang <haiyangz@microsoft.com> > Cc: sashal@kernel.org; lorenzo.pieralisi@arm.com; linux- > hyperv@vger.kernel.org; linux-pci@vger.kernel.org; KY Srinivasan > <kys@microsoft.com>; Stephen Hemminger <sthemmin@microsoft.com>; > olaf@aepfle.de; vkuznets <vkuznets@redhat.com>; linux- > kernel@vger.kernel.org > Subject: Re: [PATCH v4,1/2] PCI: hv: Detect and fix Hyper-V PCI domain > number collision > > Thanks for splitting these; I think that makes more sense. > > On Wed, Aug 14, 2019 at 12:38:54AM +0000, Haiyang Zhang wrote: > > Currently in Azure cloud, for passthrough devices including GPU, the host > > sets the device instance ID's bytes 8 - 15 to a value derived from the host > > HWID, which is the same on all devices in a VM. So, the device instance > > ID's bytes 8 and 9 provided by the host are no longer unique. This can > > cause device passthrough to VMs to fail because the bytes 8 and 9 are used > > as PCI domain number. Collision of domain numbers will cause the second > > device with the same domain number fail to load. > > I think this patch is fine. I could be misunderstanding the commit > log, but when you say "the ID bytes 8 and 9 are *no longer* unique", > that suggests that they *used* to be unique but stopped being unique > at some point, which of course raises the question of *when* they > became non-unique. > > The specific information about that point would be useful to have in > the commit log, e.g., is this related to a specific version of Azure, > a configuration change, etc? The host side change happened last year, rolled out to all azure hosts. I will put "all current azure hosts" in the commit log.
> Does this problem affect GPUs more than other passthrough devices? If > all passthrough devices are affected, why mention GPUs in particular? > I can't tell whether that information is relevant or superfluous.
We found this issue initially on multiple passthrough GPUs, I mentioned this just as an example. I will remove this word, because any PCI devices may be affected.
Thanks, - Haiyang
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