virtio: add endian-ambivalent support to VirtIODevice

Some CPU families can dynamically change their endianness. This means we
can have little endian ppc or big endian arm guests for example. This has
an impact on legacy virtio data structures since they are target endian.
We hence introduce a new property to track the endianness of each virtio
device. It is reasonnably assumed that endianness won't change while the
device is in use : we hence capture the device endianness when it gets
reset.

We migrate this property in a subsection, after the device descriptor. This
means the load code must not rely on it until it is restored. As a consequence,
the vring sanity checks had to be moved after the call to vmstate_load_state().
We enforce paranoia by poisoning the property at the begining of virtio_load().
Signed-off-by: NGreg Kurz <gkurz@linux.vnet.ibm.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio-pci.c

@@ -406,13 +406,13 @@ static uint64_t virtio_pci_config_read(void *opaque, hwaddr addr,
         break;
     case 2:
         val = virtio_config_readw(vdev, addr);
-        if (virtio_is_big_endian()) {
+        if (virtio_is_big_endian(vdev)) {
             val = bswap16(val);
         }
         break;
     case 4:
         val = virtio_config_readl(vdev, addr);
-        if (virtio_is_big_endian()) {
+        if (virtio_is_big_endian(vdev)) {
             val = bswap32(val);
         }
         break;
@@ -440,13 +440,13 @@ static void virtio_pci_config_write(void *opaque, hwaddr addr,
         virtio_config_writeb(vdev, addr, val);
         break;
     case 2:
-        if (virtio_is_big_endian()) {
+        if (virtio_is_big_endian(vdev)) {
             val = bswap16(val);
         }
         virtio_config_writew(vdev, addr, val);
         break;
     case 4:
-        if (virtio_is_big_endian()) {
+        if (virtio_is_big_endian(vdev)) {
             val = bswap32(val);
         }
         virtio_config_writel(vdev, addr, val);

hw/virtio/virtio.c

@@ -545,6 +545,27 @@ void virtio_set_status(VirtIODevice *vdev, uint8_t val)
     vdev->status = val;
 }
 
+bool target_words_bigendian(void);
+static enum virtio_device_endian virtio_default_endian(void)
+{
+    if (target_words_bigendian()) {
+        return VIRTIO_DEVICE_ENDIAN_BIG;
+    } else {
+        return VIRTIO_DEVICE_ENDIAN_LITTLE;
+    }
+}
+
+static enum virtio_device_endian virtio_current_cpu_endian(void)
+{
+    CPUClass *cc = CPU_GET_CLASS(current_cpu);
+
+    if (cc->virtio_is_big_endian(current_cpu)) {
+        return VIRTIO_DEVICE_ENDIAN_BIG;
+    } else {
+        return VIRTIO_DEVICE_ENDIAN_LITTLE;
+    }
+}
+
 void virtio_reset(void *opaque)
 {
     VirtIODevice *vdev = opaque;
@@ -552,6 +573,13 @@ void virtio_reset(void *opaque)
     int i;
 
     virtio_set_status(vdev, 0);
+    if (current_cpu) {
+        /* Guest initiated reset */
+        vdev->device_endian = virtio_current_cpu_endian();
+    } else {
+        /* System reset */
+        vdev->device_endian = virtio_default_endian();
+    }
 
     if (k->reset) {
         k->reset(vdev);
@@ -840,6 +868,24 @@ void virtio_notify_config(VirtIODevice *vdev)
     virtio_notify_vector(vdev, vdev->config_vector);
 }
 
+static bool virtio_device_endian_needed(void *opaque)
+{
+    VirtIODevice *vdev = opaque;
+
+    assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
+    return vdev->device_endian != virtio_default_endian();
+}
+
+static const VMStateDescription vmstate_virtio_device_endian = {
+    .name = "virtio/device_endian",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT8(device_endian, VirtIODevice),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 static const VMStateDescription vmstate_virtio = {
     .name = "virtio",
     .version_id = 1,
@@ -847,6 +893,13 @@ static const VMStateDescription vmstate_virtio = {
     .minimum_version_id_old = 1,
     .fields = (VMStateField[]) {
         VMSTATE_END_OF_LIST()
+    },
+    .subsections = (VMStateSubsection[]) {
+        {
+            .vmsd = &vmstate_virtio_device_endian,
+            .needed = &virtio_device_endian_needed
+        },
+        { 0 }
     }
 };
 
@@ -925,6 +978,12 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id)
     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
     VirtioDeviceClass *vdc = VIRTIO_DEVICE_GET_CLASS(vdev);
 
+    /*
+     * We poison the endianness to ensure it does not get used before
+     * subsections have been loaded.
+     */
+    vdev->device_endian = VIRTIO_DEVICE_ENDIAN_UNKNOWN;
+
     if (k->load_config) {
         ret = k->load_config(qbus->parent, f);
         if (ret)
@@ -977,18 +1036,7 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id)
         vdev->vq[i].notification = true;
 
         if (vdev->vq[i].pa) {
-            uint16_t nheads;
             virtqueue_init(&vdev->vq[i]);
-            nheads = vring_avail_idx(&vdev->vq[i]) - vdev->vq[i].last_avail_idx;
-            /* Check it isn't doing very strange things with descriptor numbers. */
-            if (nheads > vdev->vq[i].vring.num) {
-                error_report("VQ %d size 0x%x Guest index 0x%x "
-                             "inconsistent with Host index 0x%x: delta 0x%x",
-                             i, vdev->vq[i].vring.num,
-                             vring_avail_idx(&vdev->vq[i]),
-                             vdev->vq[i].last_avail_idx, nheads);
-                return -1;
-            }
         } else if (vdev->vq[i].last_avail_idx) {
             error_report("VQ %d address 0x0 "
                          "inconsistent with Host index 0x%x",
@@ -1011,7 +1059,33 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id)
         }
     }
 
-    return vmstate_load_state(f, &vmstate_virtio, vdev, 1);
+    /* Subsections */
+    ret = vmstate_load_state(f, &vmstate_virtio, vdev, 1);
+    if (ret) {
+        return ret;
+    }
+
+    if (vdev->device_endian == VIRTIO_DEVICE_ENDIAN_UNKNOWN) {
+        vdev->device_endian = virtio_default_endian();
+    }
+
+    for (i = 0; i < num; i++) {
+        if (vdev->vq[i].pa) {
+            uint16_t nheads;
+            nheads = vring_avail_idx(&vdev->vq[i]) - vdev->vq[i].last_avail_idx;
+            /* Check it isn't doing strange things with descriptor numbers. */
+            if (nheads > vdev->vq[i].vring.num) {
+                error_report("VQ %d size 0x%x Guest index 0x%x "
+                             "inconsistent with Host index 0x%x: delta 0x%x",
+                             i, vdev->vq[i].vring.num,
+                             vring_avail_idx(&vdev->vq[i]),
+                             vdev->vq[i].last_avail_idx, nheads);
+                return -1;
+            }
+        }
+    }
+
+    return 0;
 }
 
 void virtio_cleanup(VirtIODevice *vdev)
@@ -1068,6 +1142,7 @@ void virtio_init(VirtIODevice *vdev, const char *name,
     }
     vdev->vmstate = qemu_add_vm_change_state_handler(virtio_vmstate_change,
                                                      vdev);
+    vdev->device_endian = virtio_default_endian();
 }
 
 hwaddr virtio_queue_get_desc_addr(VirtIODevice *vdev, int n)

include/hw/virtio/virtio.h

@@ -104,6 +104,12 @@ typedef struct VirtQueueElement
 #define VIRTIO_DEVICE(obj) \
         OBJECT_CHECK(VirtIODevice, (obj), TYPE_VIRTIO_DEVICE)
 
+enum virtio_device_endian {
+    VIRTIO_DEVICE_ENDIAN_UNKNOWN,
+    VIRTIO_DEVICE_ENDIAN_LITTLE,
+    VIRTIO_DEVICE_ENDIAN_BIG,
+};
+
 struct VirtIODevice
 {
     DeviceState parent_obj;
@@ -121,6 +127,7 @@ struct VirtIODevice
     bool vm_running;
     VMChangeStateEntry *vmstate;
     char *bus_name;
+    uint8_t device_endian;
 };
 
 typedef struct VirtioDeviceClass {
@@ -256,9 +263,9 @@ void virtio_queue_set_host_notifier_fd_handler(VirtQueue *vq, bool assign,
 void virtio_queue_notify_vq(VirtQueue *vq);
 void virtio_irq(VirtQueue *vq);
 
-bool target_words_bigendian(void);
-static inline bool virtio_is_big_endian(void)
+static inline bool virtio_is_big_endian(VirtIODevice *vdev)
 {
-    return target_words_bigendian();
+    assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
+    return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG;
 }
 #endif