linux-kernel - RE: [PATCH v2] PCI: hv: Detect and fix Hyper-V PCI domain number collision

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Message-ID: <DM6PR21MB13379DCB3007D728204A0D8CCAD30@DM6PR21MB1337.namprd21.prod.outlook.com>
Date:   Mon, 12 Aug 2019 13:50:34 +0000
From:   Haiyang Zhang <haiyangz@...rosoft.com>
To:     "sashal@...nel.org" <sashal@...nel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>, vkuznets <vkuznets@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] PCI: hv: Detect and fix Hyper-V PCI domain number
 collision



> -----Original Message-----
> From: LKML haiyangz <lkmlhyz@...rosoft.com> On Behalf Of Haiyang
> Zhang
> Sent: Tuesday, August 6, 2019 7:52 PM
> To: sashal@...nel.org; bhelgaas@...gle.com; lorenzo.pieralisi@....com;
> linux-hyperv@...r.kernel.org; linux-pci@...r.kernel.org
> Cc: Haiyang Zhang <haiyangz@...rosoft.com>; KY Srinivasan
> <kys@...rosoft.com>; Stephen Hemminger <sthemmin@...rosoft.com>;
> olaf@...fle.de; vkuznets <vkuznets@...hat.com>; linux-
> kernel@...r.kernel.org
> Subject: [PATCH v2] PCI: hv: Detect and fix Hyper-V PCI domain number
> collision
> 
> 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 is used as PCI domain number. So, as recommended by Azure host team,
> we now use the bytes 4 and 5 which usually contain unique numbers as PCI
> domain. The chance of collision is greatly reduced. In the rare cases of
> collision, we will detect and find another number that is not in use.
> 
> Thanks to Michael Kelley <mikelley@...rosoft.com> for proposing this idea.
> 
> Signed-off-by: Haiyang Zhang <haiyangz@...rosoft.com>
> Acked-by: Sasha Levin <sashal@...nel.org>
> ---
>  drivers/pci/controller/pci-hyperv.c | 92

Hi Lorenzo,

This patch has been updated based on Bjorn's comments. Do you have any further
comments? Could you take it from your tree?

Thanks,
- Haiyang