[Qemu-devel] [PATCH] Remove PCI class code from virtio balloon device

[David Gibson <david@gibson.dropbear.id.au>]

Currently the virtio balloon device, when using the virtio-pci interface
advertises itself with PCI class code MEMORY_RAM.  This is wrong; the
balloon is vaguely related to memory, but is nothing like a PCI memory
device in the meaning of the class code, and this code is not required or
suggested by the virtio PCI specification.

Worse, this patch causes problems on the pseries machine, because the
firmware, seeing this class code, advertises the device as memory in the
device tree, and then a guest kernel bug causes it to see this "memory"
before the real system memory, leading to a crash in early boot.

This patch fixes the problem by removing the bogus PCI class code on the
balloon device.  The backwards compatibility PC machines get new compat
properties so that they don't change.

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 hw/pc_piix.c    |   24 ++++++++++++++++++++++++
 hw/virtio-pci.c |    7 ++++++-
 2 files changed, 30 insertions(+), 1 deletions(-)


diff --git a/hw/pc_piix.c b/hw/pc_piix.c
index 3f99f9a..72a4250 100644
--- a/hw/pc_piix.c
+++ b/hw/pc_piix.c
@@ -386,6 +386,10 @@ static QEMUMachine pc_machine_v1_0 = {
             .driver   = "isa-fdc",
             .property = "check_media_rate",
             .value    = "off",
+        }, {
+            .driver   = "virtio-balloon-pci",
+            .property = "class",
+            .value    = stringify(PCI_CLASS_MEMORY_RAM),
         },
         { /* end of list */ }
     },
@@ -449,6 +453,10 @@ static QEMUMachine pc_machine_v0_14 = {
             .driver   = "pc-sysfw",
             .property = "rom_only",
             .value    = stringify(1),
+        }, {
+            .driver   = "virtio-balloon-pci",
+            .property = "class",
+            .value    = stringify(PCI_CLASS_MEMORY_RAM),
         },
         { /* end of list */ }
     },
@@ -505,6 +513,10 @@ static QEMUMachine pc_machine_v0_13 = {
             .driver   = "pc-sysfw",
             .property = "rom_only",
             .value    = stringify(1),
+        }, {
+            .driver   = "virtio-balloon-pci",
+            .property = "class",
+            .value    = stringify(PCI_CLASS_MEMORY_RAM),
         },
         { /* end of list */ }
     },
@@ -565,6 +577,10 @@ static QEMUMachine pc_machine_v0_12 = {
             .driver   = "pc-sysfw",
             .property = "rom_only",
             .value    = stringify(1),
+        }, {
+            .driver   = "virtio-balloon-pci",
+            .property = "class",
+            .value    = stringify(PCI_CLASS_MEMORY_RAM),
         },
         { /* end of list */ }
     }
@@ -633,6 +649,10 @@ static QEMUMachine pc_machine_v0_11 = {
             .driver   = "pc-sysfw",
             .property = "rom_only",
             .value    = stringify(1),
+        }, {
+            .driver   = "virtio-balloon-pci",
+            .property = "class",
+            .value    = stringify(PCI_CLASS_MEMORY_RAM),
         },
         { /* end of list */ }
     }
@@ -713,6 +733,10 @@ static QEMUMachine pc_machine_v0_10 = {
             .driver   = "pc-sysfw",
             .property = "rom_only",
             .value    = stringify(1),
+        }, {
+            .driver   = "virtio-balloon-pci",
+            .property = "class",
+            .value    = stringify(PCI_CLASS_MEMORY_RAM),
         },
         { /* end of list */ }
     },
diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index a0fb7c1..1fd5768 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -790,6 +790,10 @@ static int virtio_balloon_init_pci(PCIDevice *pci_dev)
     VirtIOPCIProxy *proxy = DO_UPCAST(VirtIOPCIProxy, pci_dev, pci_dev);
     VirtIODevice *vdev;
 
+    if (proxy->class_code != PCI_CLASS_OTHERS &&
+        proxy->class_code != PCI_CLASS_MEMORY_RAM) /* qemu < 1.1 */
+        proxy->class_code = PCI_CLASS_OTHERS;
+
     vdev = virtio_balloon_init(&pci_dev->qdev);
     if (!vdev) {
         return -1;
@@ -905,6 +909,7 @@ static TypeInfo virtio_serial_info = {
 };
 
 static Property virtio_balloon_properties[] = {
+    DEFINE_PROP_HEX32("class", VirtIOPCIProxy, class_code, PCI_CLASS_OTHERS),
     DEFINE_VIRTIO_COMMON_FEATURES(VirtIOPCIProxy, host_features),
     DEFINE_PROP_END_OF_LIST(),
 };
@@ -919,7 +924,7 @@ static void virtio_balloon_class_init(ObjectClass *klass, void *data)
     k->vendor_id = PCI_VENDOR_ID_REDHAT_QUMRANET;
     k->device_id = PCI_DEVICE_ID_VIRTIO_BALLOON;
     k->revision = VIRTIO_PCI_ABI_VERSION;
-    k->class_id = PCI_CLASS_MEMORY_RAM;
+    k->class_id = PCI_CLASS_OTHERS;
     dc->reset = virtio_pci_reset;
     dc->props = virtio_balloon_properties;
 }
-- 
1.7.9.1