virtio-pci: fix migration for pci bus master

Current support for bus master (clearing OK bit) together with the need to
support guests which do not enable PCI bus mastering, leads to extra state in
VIRTIO_PCI_FLAG_BUS_MASTER_BUG bit, which isn't robust in case of cross-version
migration for the case when guests use the device before setting DRIVER_OK.

Rip out this code, and replace it:
-   Modern QEMU doesn't need VIRTIO_PCI_FLAG_BUS_MASTER_BUG
    so just drop it for latest machine type.
-   For compat machine types, set PCI_COMMAND if DRIVER_OK
    is set.

As this is needed for 2.1 for both pc and ppc, move PC_COMPAT macros from pc.h
to a new common header.

Cc: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Alexander Graf <agraf@suse.de>

hw/i386/pc_piix.c

@@ -474,7 +474,7 @@ static QEMUMachine pc_i440fx_machine_v2_1 = {
     .name = "pc-i440fx-2.1",
     .init = pc_init_pci,
     .compat_props = (GlobalProperty[]) {
-        PC_COMPAT_2_1,
+        HW_COMPAT_2_1,
         { /* end of list */ }
     },
 };

hw/i386/pc_q35.c

@@ -370,7 +370,7 @@ static QEMUMachine pc_q35_machine_v2_1 = {
     .name = "pc-q35-2.1",
     .init = pc_q35_init,
     .compat_props = (GlobalProperty[]) {
-        PC_COMPAT_2_1,
+        HW_COMPAT_2_1,
         { /* end of list */ }
     },
 };

hw/ppc/spapr.c

@@ -57,6 +57,8 @@
 #include "trace.h"
 #include "hw/nmi.h"
 
+#include "hw/compat.h"
+
 #include <libfdt.h>
 
 /* SLOF memory layout:
@@ -1689,10 +1691,15 @@ static const TypeInfo spapr_machine_info = {
 static void spapr_machine_2_1_class_init(ObjectClass *oc, void *data)
 {
     MachineClass *mc = MACHINE_CLASS(oc);
+    static GlobalProperty compat_props[] = {
+        HW_COMPAT_2_1,
+        { /* end of list */ }
+    };
 
     mc->name = "pseries-2.1";
     mc->desc = "pSeries Logical Partition (PAPR compliant) v2.1";
     mc->is_default = 0;
+    mc->compat_props = compat_props;
 }
 
 static const TypeInfo spapr_machine_2_1_info = {

hw/virtio/virtio-pci.c

@@ -86,9 +86,6 @@
  * 12 is historical, and due to x86 page size. */
 #define VIRTIO_PCI_QUEUE_ADDR_SHIFT    12
 
-/* Flags track per-device state like workarounds for quirks in older guests. */
-#define VIRTIO_PCI_FLAG_BUS_MASTER_BUG  (1 << 0)
-
 static void virtio_pci_bus_new(VirtioBusState *bus, size_t bus_size,
                                VirtIOPCIProxy *dev);
 
@@ -323,14 +320,6 @@ static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val)
                                      proxy->pci_dev.config[PCI_COMMAND] |
                                      PCI_COMMAND_MASTER, 1);
         }
-
-        /* Linux before 2.6.34 sets the device as OK without enabling
-           the PCI device bus master bit. In this case we need to disable
-           some safety checks. */
-        if ((val & VIRTIO_CONFIG_S_DRIVER_OK) &&
-            !(proxy->pci_dev.config[PCI_COMMAND] & PCI_COMMAND_MASTER)) {
-            proxy->flags |= VIRTIO_PCI_FLAG_BUS_MASTER_BUG;
-        }
         break;
     case VIRTIO_MSI_CONFIG_VECTOR:
         msix_vector_unuse(&proxy->pci_dev, vdev->config_vector);
@@ -483,8 +472,7 @@ static void virtio_write_config(PCIDevice *pci_dev, uint32_t address,
     pci_default_write_config(pci_dev, address, val, len);
 
     if (range_covers_byte(address, len, PCI_COMMAND) &&
-        !(pci_dev->config[PCI_COMMAND] & PCI_COMMAND_MASTER) &&
+        !(pci_dev->config[PCI_COMMAND] & PCI_COMMAND_MASTER)) {
-        !(proxy->flags & VIRTIO_PCI_FLAG_BUS_MASTER_BUG)) {
         virtio_pci_stop_ioeventfd(proxy);
         virtio_set_status(vdev, vdev->status & ~VIRTIO_CONFIG_S_DRIVER_OK);
     }
@@ -895,11 +883,15 @@ static void virtio_pci_vmstate_change(DeviceState *d, bool running)
     VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
 
     if (running) {
-        /* Try to find out if the guest has bus master disabled, but is
+        /* Old QEMU versions did not set bus master enable on status write.
-           in ready state. Then we have a buggy guest OS. */
+         * Detect DRIVER set and enable it.
-        if ((vdev->status & VIRTIO_CONFIG_S_DRIVER_OK) &&
+         */
+        if ((proxy->flags & VIRTIO_PCI_FLAG_BUS_MASTER_BUG_MIGRATION) &&
+            (vdev->status & VIRTIO_CONFIG_S_DRIVER) &&
             !(proxy->pci_dev.config[PCI_COMMAND] & PCI_COMMAND_MASTER)) {
-            proxy->flags |= VIRTIO_PCI_FLAG_BUS_MASTER_BUG;
+            pci_default_write_config(&proxy->pci_dev, PCI_COMMAND,
+                                     proxy->pci_dev.config[PCI_COMMAND] |
+                                     PCI_COMMAND_MASTER, 1);
         }
         virtio_pci_start_ioeventfd(proxy);
     } else {
@@ -1040,10 +1032,11 @@ static void virtio_pci_reset(DeviceState *qdev)
     virtio_pci_stop_ioeventfd(proxy);
     virtio_bus_reset(bus);
     msix_unuse_all_vectors(&proxy->pci_dev);
-    proxy->flags &= ~VIRTIO_PCI_FLAG_BUS_MASTER_BUG;
 }
 
 static Property virtio_pci_properties[] = {
+    DEFINE_PROP_BIT("virtio-pci-bus-master-bug-migration", VirtIOPCIProxy, flags,
+                    VIRTIO_PCI_FLAG_BUS_MASTER_BUG_MIGRATION_BIT, false),
     DEFINE_VIRTIO_COMMON_FEATURES(VirtIOPCIProxy, host_features),
     DEFINE_PROP_END_OF_LIST(),
 };

hw/virtio/virtio-pci.h

@@ -53,6 +53,11 @@ typedef struct VirtioBusClass VirtioPCIBusClass;
 #define VIRTIO_PCI_BUS_CLASS(klass) \
         OBJECT_CLASS_CHECK(VirtioPCIBusClass, klass, TYPE_VIRTIO_PCI_BUS)
 
+/* Need to activate work-arounds for buggy guests at vmstate load. */
+#define VIRTIO_PCI_FLAG_BUS_MASTER_BUG_MIGRATION_BIT  0
+#define VIRTIO_PCI_FLAG_BUS_MASTER_BUG_MIGRATION \
+    (1 << VIRTIO_PCI_FLAG_BUS_MASTER_BUG_MIGRATION_BIT)
+
 /* Performance improves when virtqueue kick processing is decoupled from the
  * vcpu thread using ioeventfd for some devices. */
 #define VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT 1

include/hw/compat.h

@@ -0,0 +1,35 @@
+#ifndef HW_COMPAT_H
+#define HW_COMPAT_H
+
+#define HW_COMPAT_2_1 \
+        {\
+            .driver   = "intel-hda",\
+            .property = "old_msi_addr",\
+            .value    = "on",\
+        },{\
+            .driver   = "VGA",\
+            .property = "qemu-extended-regs",\
+            .value    = "off",\
+        },{\
+            .driver   = "secondary-vga",\
+            .property = "qemu-extended-regs",\
+            .value    = "off",\
+        },{\
+            .driver   = "virtio-scsi-pci",\
+            .property = "any_layout",\
+            .value    = "off",\
+        },{\
+            .driver   = "usb-mouse",\
+            .property = "usb_version",\
+            .value    = stringify(1),\
+        },{\
+            .driver   = "usb-kbd",\
+            .property = "usb_version",\
+            .value    = stringify(1),\
+        },{\
+            .driver   = "virtio-pci",\
+            .property = "virtio-pci-bus-master-bug-migration",\
+            .value    = "on",\
+        }
+
+#endif /* HW_COMPAT_H */

include/hw/i386/pc.h

@@ -14,6 +14,7 @@
 #include "sysemu/sysemu.h"
 #include "hw/pci/pci.h"
 #include "hw/boards.h"
+#include "hw/compat.h"
 
 #define HPET_INTCAP "hpet-intcap"
 
@@ -301,31 +302,8 @@ int e820_add_entry(uint64_t, uint64_t, uint32_t);
 int e820_get_num_entries(void);
 bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
 
-#define PC_COMPAT_2_1 \
-        {\
-            .driver   = "intel-hda",\
-            .property = "old_msi_addr",\
-            .value    = "on",\
-        },{\
-            .driver   = "VGA",\
-            .property = "qemu-extended-regs",\
-            .value    = "off",\
-        },{\
-            .driver   = "secondary-vga",\
-            .property = "qemu-extended-regs",\
-            .value    = "off",\
-        },{\
-            .driver   = "usb-mouse",\
-            .property = "usb_version",\
-            .value    = stringify(1),\
-        },{\
-            .driver   = "usb-kbd",\
-            .property = "usb_version",\
-            .value    = stringify(1),\
-        }
-
 #define PC_COMPAT_2_0 \
-        PC_COMPAT_2_1, \
+        HW_COMPAT_2_1, \
         {\
             .driver   = "virtio-scsi-pci",\
             .property = "any_layout",\