On 6/21/2019 12:55 AM, Alex Williamson wrote:
> On Thu, 20 Jun 2019 20:07:36 +0530
> Kirti Wankhede <kwankh...@nvidia.com> wrote:
>
>> Added .save_live_pending, .save_live_iterate and .save_live_complete_precopy
>> functions. These functions handles pre-copy and stop-and-copy phase.
>>
>> In _SAVING|_RUNNING device state or pre-copy phase:
>> - read pending_bytes
>> - read data_offset - indicates kernel driver to write data to staging
>> buffer which is mmapped.
>
> Why is data_offset the trigger rather than data_size? It seems that
> data_offset can't really change dynamically since it might be mmap'd,
> so it seems unnatural to bother re-reading it.
>
Vendor driver can change data_offset, he can have different data_offset
for device data and dirty pages bitmap.
>> - read data_size - amount of data in bytes written by vendor driver in
>> migration
>> region.
>> - if data section is trapped, pread() number of bytes in data_size, from
>> data_offset.
>> - if data section is mmaped, read mmaped buffer of size data_size.
>> - Write data packet to file stream as below:
>> {VFIO_MIG_FLAG_DEV_DATA_STATE, data_size, actual data,
>> VFIO_MIG_FLAG_END_OF_STATE }
>>
>> In _SAVING device state or stop-and-copy phase
>> a. read config space of device and save to migration file stream. This
>> doesn't need to be from vendor driver. Any other special config state
>> from driver can be saved as data in following iteration.
>> b. read pending_bytes - indicates kernel driver to write data to staging
>> buffer which is mmapped.
>
> Is it pending_bytes or data_offset that triggers the write out of
> data? Why pending_bytes vs data_size? I was interpreting
> pending_bytes as the total data size while data_size is the size
> available to read now, so assumed data_size would be more closely
> aligned to making the data available.
>
Sorry, that's my mistake while editing, its read data_offset as in above
case.
>> c. read data_size - amount of data in bytes written by vendor driver in
>> migration region.
>> d. if data section is trapped, pread() from data_offset of size data_size.
>> e. if data section is mmaped, read mmaped buffer of size data_size.
>
> Should this read as "pread() from data_offset of data_size, or
> optionally if mmap is supported on the data area, read data_size from
> start of mapped buffer"? IOW, pread should always work. Same in
> previous section.
>
ok. I'll update.
>> f. Write data packet as below:
>> {VFIO_MIG_FLAG_DEV_DATA_STATE, data_size, actual data}
>> g. iterate through steps b to f until (pending_bytes > 0)
>
> s/until/while/
Ok.
>
>> h. Write {VFIO_MIG_FLAG_END_OF_STATE}
>>
>> .save_live_iterate runs outside the iothread lock in the migration case,
>> which
>> could race with asynchronous call to get dirty page list causing data
>> corruption
>> in mapped migration region. Mutex added here to serial migration buffer read
>> operation.
>
> Would we be ahead to use different offsets within the region for device
> data vs dirty bitmap to avoid this?
>
Lock will still be required to serialize the read/write operations on
vfio_device_migration_info structure in the region.
>> Signed-off-by: Kirti Wankhede <kwankh...@nvidia.com>
>> Reviewed-by: Neo Jia <c...@nvidia.com>
>> ---
>> hw/vfio/migration.c | 212
>> ++++++++++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 212 insertions(+)
>>
>> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
>> index fe0887c27664..0a2f30872316 100644
>> --- a/hw/vfio/migration.c
>> +++ b/hw/vfio/migration.c
>> @@ -107,6 +107,111 @@ static int vfio_migration_set_state(VFIODevice
>> *vbasedev, uint32_t state)
>> return 0;
>> }
>>
>> +static int vfio_save_buffer(QEMUFile *f, VFIODevice *vbasedev)
>> +{
>> + VFIOMigration *migration = vbasedev->migration;
>> + VFIORegion *region = &migration->region.buffer;
>> + uint64_t data_offset = 0, data_size = 0;
>> + int ret;
>> +
>> + ret = pread(vbasedev->fd, &data_offset, sizeof(data_offset),
>> + region->fd_offset + offsetof(struct
>> vfio_device_migration_info,
>> + data_offset));
>> + if (ret != sizeof(data_offset)) {
>> + error_report("Failed to get migration buffer data offset %d",
>> + ret);
>> + return -EINVAL;
>> + }
>> +
>> + ret = pread(vbasedev->fd, &data_size, sizeof(data_size),
>> + region->fd_offset + offsetof(struct
>> vfio_device_migration_info,
>> + data_size));
>> + if (ret != sizeof(data_size)) {
>> + error_report("Failed to get migration buffer data size %d",
>> + ret);
>> + return -EINVAL;
>> + }
>> +
>> + if (data_size > 0) {
>> + void *buf = NULL;
>> + bool buffer_mmaped = false;
>> +
>> + if (region->mmaps) {
>> + int i;
>> +
>> + for (i = 0; i < region->nr_mmaps; i++) {
>> + if ((data_offset >= region->mmaps[i].offset) &&
>> + (data_offset < region->mmaps[i].offset +
>> + region->mmaps[i].size)) {
>> + buf = region->mmaps[i].mmap + (data_offset -
>> + region->mmaps[i].offset);
>
> So you're expecting that data_offset is somewhere within the data
> area. Why doesn't the data always simply start at the beginning of the
> data area? ie. data_offset would coincide with the beginning of the
> mmap'able area (if supported) and be static. Does this enable some
> functionality in the vendor driver?
Do you want to enforce that to vendor driver?
>From the feedback on previous version I thought vendor driver should
define data_offset within the region
"I'd suggest that the vendor driver expose a read-only
data_offset that matches a sparse mmap capability entry should the
driver support mmap. The use should always read or write data from the
vendor defined data_offset"
This also adds flexibility to vendor driver such that vendor driver can
define different data_offset for device data and dirty page bitmap
within same mmaped region.
> Does resume data need to be
> written from the same offset where it's read?
No, resume data should be written from the data_offset that vendor
driver provided during resume.
>
>> + buffer_mmaped = true;
>> + break;
>> + }
>> + }
>> + }
>> +
>> + if (!buffer_mmaped) {
>> + buf = g_malloc0(data_size);
>> + ret = pread(vbasedev->fd, buf, data_size,
>> + region->fd_offset + data_offset);
>> + if (ret != data_size) {
>> + error_report("Failed to get migration data %d", ret);
>> + g_free(buf);
>> + return -EINVAL;
>> + }
>> + }
>> +
>> + qemu_put_be64(f, data_size);
>> + qemu_put_buffer(f, buf, data_size);
>> +
>> + if (!buffer_mmaped) {
>> + g_free(buf);
>> + }
>> + migration->pending_bytes -= data_size;
>> + } else {
>> + qemu_put_be64(f, data_size);
>> + }
>> +
>> + ret = qemu_file_get_error(f);
>> +
>> + return data_size;
>> +}
>> +
>> +static int vfio_update_pending(VFIODevice *vbasedev)
>> +{
>> + VFIOMigration *migration = vbasedev->migration;
>> + VFIORegion *region = &migration->region.buffer;
>> + uint64_t pending_bytes = 0;
>> + int ret;
>> +
>> + ret = pread(vbasedev->fd, &pending_bytes, sizeof(pending_bytes),
>> + region->fd_offset + offsetof(struct
>> vfio_device_migration_info,
>> + pending_bytes));
>
> Did this trigger the vendor driver to write out to the data area when
> we don't need it to?
>
No, as I mentioned above, I'll update the description.
Thanks,
Kirti
>> + if ((ret < 0) || (ret != sizeof(pending_bytes))) {
>> + error_report("Failed to get pending bytes %d", ret);
>> + migration->pending_bytes = 0;
>> + return (ret < 0) ? ret : -EINVAL;
>> + }
>> +
>> + migration->pending_bytes = pending_bytes;
>> + return 0;
>> +}
>> +
>> +static int vfio_save_device_config_state(QEMUFile *f, void *opaque)
>> +{
>> + VFIODevice *vbasedev = opaque;
>> +
>> + qemu_put_be64(f, VFIO_MIG_FLAG_DEV_CONFIG_STATE);
>> +
>> + if (vbasedev->type == VFIO_DEVICE_TYPE_PCI) {
>> + vfio_pci_save_config(vbasedev, f);
>> + }
>> + qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
>> +
>> + return qemu_file_get_error(f);
>> +}
>> +
>> /* ---------------------------------------------------------------------- */
>>
>> static int vfio_save_setup(QEMUFile *f, void *opaque)
>> @@ -163,9 +268,116 @@ static void vfio_save_cleanup(void *opaque)
>> }
>> }
>>
>> +static void vfio_save_pending(QEMUFile *f, void *opaque,
>> + uint64_t threshold_size,
>> + uint64_t *res_precopy_only,
>> + uint64_t *res_compatible,
>> + uint64_t *res_postcopy_only)
>> +{
>> + VFIODevice *vbasedev = opaque;
>> + VFIOMigration *migration = vbasedev->migration;
>> + int ret;
>> +
>> + ret = vfio_update_pending(vbasedev);
>> + if (ret) {
>> + return;
>> + }
>> +
>> + if (vbasedev->device_state & VFIO_DEVICE_STATE_RUNNING) {
>> + *res_precopy_only += migration->pending_bytes;
>> + } else {
>> + *res_postcopy_only += migration->pending_bytes;
>> + }
>> + *res_compatible += 0;
>> +}
>> +
>> +static int vfio_save_iterate(QEMUFile *f, void *opaque)
>> +{
>> + VFIODevice *vbasedev = opaque;
>> + VFIOMigration *migration = vbasedev->migration;
>> + int ret;
>> +
>> + qemu_put_be64(f, VFIO_MIG_FLAG_DEV_DATA_STATE);
>> +
>> + qemu_mutex_lock(&migration->lock);
>> + ret = vfio_save_buffer(f, vbasedev);
>> + qemu_mutex_unlock(&migration->lock);
>> +
>> + if (ret < 0) {
>> + error_report("vfio_save_buffer failed %s",
>> + strerror(errno));
>> + return ret;
>> + }
>> +
>> + qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
>> +
>> + ret = qemu_file_get_error(f);
>> + if (ret) {
>> + return ret;
>> + }
>> +
>> + return ret;
>> +}
>> +
>> +static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
>> +{
>> + VFIODevice *vbasedev = opaque;
>> + VFIOMigration *migration = vbasedev->migration;
>> + int ret;
>> +
>> + ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_SAVING);
>> + if (ret) {
>> + error_report("Failed to set state STOP and SAVING");
>> + return ret;
>> + }
>> +
>> + ret = vfio_save_device_config_state(f, opaque);
>> + if (ret) {
>> + return ret;
>> + }
>> +
>> + ret = vfio_update_pending(vbasedev);
>> + if (ret) {
>> + return ret;
>> + }
>> +
>> + while (migration->pending_bytes > 0) {
>> + qemu_put_be64(f, VFIO_MIG_FLAG_DEV_DATA_STATE);
>> + ret = vfio_save_buffer(f, vbasedev);
>> + if (ret < 0) {
>> + error_report("Failed to save buffer");
>> + return ret;
>> + } else if (ret == 0) {
>> + break;
>> + }
>> +
>> + ret = vfio_update_pending(vbasedev);
>> + if (ret) {
>> + return ret;
>> + }
>> + }
>> +
>> + qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
>> +
>> + ret = qemu_file_get_error(f);
>> + if (ret) {
>> + return ret;
>> + }
>> +
>> + ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_STOPPED);
>> + if (ret) {
>> + error_report("Failed to set state STOPPED");
>> + return ret;
>> + }
>> + return ret;
>> +}
>> +
>> static SaveVMHandlers savevm_vfio_handlers = {
>> .save_setup = vfio_save_setup,
>> .save_cleanup = vfio_save_cleanup,
>> + .save_live_pending = vfio_save_pending,
>> + .save_live_iterate = vfio_save_iterate,
>> + .save_live_complete_precopy = vfio_save_complete_precopy,
>> };
>>
>> /* ---------------------------------------------------------------------- */
>
