On 13/12/22 09:03, Thomas Huth wrote:
On 13/12/2022 08.30, Philippe Mathieu-Daudé wrote:
On 13/12/22 01:14, Richard Henderson wrote:
On 12/12/22 17:05, Philippe Mathieu-Daudé wrote:
The device endianness doesn't change during runtime.
What are you talking about? Of course it does.
The host CPU certainly does, but the virtio device doesn't... Does it?
This check only consider the device, not the CPU:
bool virtio_access_is_big_endian(VirtIODevice *vdev)
{
#if defined(LEGACY_VIRTIO_IS_BIENDIAN)
return virtio_is_big_endian(vdev);
#elif TARGET_BIG_ENDIAN
if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) {
/*Devices conforming to VIRTIO 1.0 or later are always LE.*/
return false;
}
return true;
Well, this part here means that the endianness can indeed change on the
device side during runtime. Depending on whether VIRTIO_F_VERSION_1 is
negotiated or not, the device is little or big endian. Happens on s390x
for example - for legacy virtio, big endian is used, and for modern
virtio, little endian is used instead.
virtio_is_big_endian() depends on vdev->device_endian which is set in:
1) virtio_init()
void virtio_init(VirtIODevice *vdev, uint16_t device_id,
size_t config_size)
{
....
vdev->device_endian = virtio_default_endian();
2) virtio_load()
int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id)
{
int i, ret;
int32_t config_len;
uint32_t num;
uint32_t features;
BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
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 (vdev->device_endian == VIRTIO_DEVICE_ENDIAN_UNKNOWN) {
vdev->device_endian = virtio_default_endian();
}
3) virtio_reset()
void virtio_reset(void *opaque)
{
VirtIODevice *vdev = opaque;
VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
int i;
virtio_set_status(vdev, 0);
if (current_cpu) {
/* Guest initiated reset */
vdev->device_endian = virtio_current_cpu_endian();