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[Qemu-devel] [PATCH v2] virtio-pci: Don't force Subsystem Vendor ID = Ve

From: Ladi Prosek
Subject: [Qemu-devel] [PATCH v2] virtio-pci: Don't force Subsystem Vendor ID = Vendor ID
Date: Mon, 13 Nov 2017 09:45:58 +0100

The statement being removed doesn't change anything as virtio PCI devices 
have Subsystem Vendor ID set to pci_default_sub_vendor_id (0x1af4), same as 
ID. And the Virtio spec does not require the two to be equal, either:

  "The PCI Subsystem Vendor ID and the PCI Subsystem Device ID MAY reflect the 
  Vendor and Device ID of the environment (for informational purposes by the 


Following the recent virtio-win licensing change, several vendors are planning 
ship their own certified version of Windows guest Virtio drivers, potentially 
advantage of Windows Update as a distribution channel. It is therefore critical 
each vendor uses their own PCI Subsystem Vendor ID for Virtio devices to prevent
drivers from other vendors binding to it.

This would be trivially done by adding:

  k->subsystem_vendor_id = ...

to virtio_pci_class_init(). Except for the problematic statement deleted by this
patch, which reverts the Subsystem Vendor ID back to 0x1af4 for legacy devices 
no good reason.

Signed-off-by: Ladi Prosek <address@hidden>

* Added a comment about the default Subsystem Vendor ID.

 hw/virtio/virtio-pci.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index e92837c42b..148621d9c7 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -1588,9 +1588,11 @@ static void virtio_pci_device_plugged(DeviceState *d, 
Error **errp)
                        "neither legacy nor transitional device.");
             return ;
-        /* legacy and transitional */
-        pci_set_word(config + PCI_SUBSYSTEM_VENDOR_ID,
-                     pci_get_word(config + PCI_VENDOR_ID));
+        /*
+         * Legacy and transitional devices use specific subsystem IDs.
+         * Note that the subsystem vendor ID (config + PCI_SUBSYSTEM_VENDOR_ID)
+         * is set to PCI_SUBVENDOR_ID_REDHAT_QUMRANET by default.
+         */
         pci_set_word(config + PCI_SUBSYSTEM_ID, virtio_bus_get_vdev_id(bus));
     } else {
         /* pure virtio-1.0 */

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