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Re: [Qemu-devel] [PATCH v4 08/13] vfio: Add save state functions to Save
From: |
Kirti Wankhede |
Subject: |
Re: [Qemu-devel] [PATCH v4 08/13] vfio: Add save state functions to SaveVMHandlers |
Date: |
Sat, 22 Jun 2019 01:08:40 +0530 |
On 6/21/2019 8:46 PM, Alex Williamson wrote:
> On Fri, 21 Jun 2019 12:08:26 +0530
> Kirti Wankhede <address@hidden> wrote:
>
>> On 6/21/2019 12:55 AM, Alex Williamson wrote:
>>> On Thu, 20 Jun 2019 20:07:36 +0530
>>> Kirti Wankhede <address@hidden> 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 <address@hidden>
>>>> Reviewed-by: Neo Jia <address@hidden>
>>>> ---
>>>> 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.
>
> I agree, it adds flexibility, the protocol was not evident to me until
> I got here though.
>
>>> 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.
>
> s/resume/save/?
>
> Or is this saying that on resume that the vendor driver is requesting a
> specific block of data via data_offset?
Correct.
Thanks,
Kirti
> I think resume is going to be
> directed by the user, writing in the same order they received the
> data. Thanks,
>
> Alex
>
>>>> + 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,
>>>> };
>>>>
>>>> /* ----------------------------------------------------------------------
>>>> */
>>>
>
- Re: [Qemu-devel] [PATCH v4 07/13] vfio: Register SaveVMHandlers for VFIO device, (continued)
- [Qemu-devel] [PATCH v4 06/13] vfio: Add migration state change notifier, Kirti Wankhede, 2019/06/20
- [Qemu-devel] [PATCH v4 04/13] vfio: Add migration region initialization and finalize function, Kirti Wankhede, 2019/06/20
- [Qemu-devel] [PATCH v4 08/13] vfio: Add save state functions to SaveVMHandlers, Kirti Wankhede, 2019/06/20
- Re: [Qemu-devel] [PATCH v4 08/13] vfio: Add save state functions to SaveVMHandlers, Alex Williamson, 2019/06/20
- Re: [Qemu-devel] [PATCH v4 08/13] vfio: Add save state functions to SaveVMHandlers, Kirti Wankhede, 2019/06/21
- Re: [Qemu-devel] [PATCH v4 08/13] vfio: Add save state functions to SaveVMHandlers, Alex Williamson, 2019/06/21
- Re: [Qemu-devel] [PATCH v4 08/13] vfio: Add save state functions to SaveVMHandlers,
Kirti Wankhede <=
- Re: [Qemu-devel] [PATCH v4 08/13] vfio: Add save state functions to SaveVMHandlers, Alex Williamson, 2019/06/21
- Re: [Qemu-devel] [PATCH v4 08/13] vfio: Add save state functions to SaveVMHandlers, Kirti Wankhede, 2019/06/21
- Re: [Qemu-devel] [PATCH v4 08/13] vfio: Add save state functions to SaveVMHandlers, Alex Williamson, 2019/06/21
- Re: [Qemu-devel] [PATCH v4 08/13] vfio: Add save state functions to SaveVMHandlers, Kirti Wankhede, 2019/06/21
- Re: [Qemu-devel] [PATCH v4 08/13] vfio: Add save state functions to SaveVMHandlers, Alex Williamson, 2019/06/21
- Re: [Qemu-devel] [PATCH v4 08/13] vfio: Add save state functions to SaveVMHandlers, Kirti Wankhede, 2019/06/24
Re: [Qemu-devel] [PATCH v4 08/13] vfio: Add save state functions to SaveVMHandlers, Yan Zhao, 2019/06/20