[bionic:linux-azure-4.15][PATCH 5/5] PCI: hv: Use bytes 4 and 5 from instance ID as the PCI domain numbers

[Marcelo Henrique Cerri]

From: Haiyang Zhang <haiyangz at microsoft.com>

BugLink: https://bugs.launchpad.net/bugs/1867220

As recommended by Azure host team, the bytes 4, 5 have more uniqueness
(info entropy) than bytes 8, 9 so use them as the PCI domain numbers.

On older hosts, bytes 4, 5 can also be used -- no backward compatibility
issues are introduced and the chance of collision is greatly reduced.

In the rare cases of collision, the driver code detects and finds
another number that is not in use.

Suggested-by: Michael Kelley <mikelley at microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz at microsoft.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
Acked-by: Sasha Levin <sashal at kernel.org>
(backported from commit f73f8a504e27959576a2f4d85182202561e426f2)
[marcelo.cerri at canonical.com: basically a clean cherry-pick, but the
 changes from drivers/pci/controller/pci-hyperv.c had to be applied
 to drivers/pci/host/pci-hyperv.c instead]
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>
---
 drivers/pci/host/pci-hyperv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/host/pci-hyperv.c b/drivers/pci/host/pci-hyperv.c
index c414255d2ae6..81da709aa757 100644
--- a/drivers/pci/host/pci-hyperv.c
+++ b/drivers/pci/host/pci-hyperv.c
@@ -2632,7 +2632,7 @@ static int hv_pci_probe(struct hv_device *hdev,
 	 * (2) There will be no overlap between domains (after fixing possible
 	 * collisions) in the same VM.
 	 */
-	dom_req = hdev->dev_instance.b[8] << 8 | hdev->dev_instance.b[9];
+	dom_req = hdev->dev_instance.b[5] << 8 | hdev->dev_instance.b[4];
 	dom = hv_get_dom_num(dom_req);
 
 	if (dom == HVPCI_DOM_INVALID) {
-- 
2.25.1