Re: [Qemu-devel] [PATCH v7 09/13] vfio: Add save state functions to SaveVMHandlers

[Kirti Wankhede]

On 7/12/2019 8:14 AM, Yan Zhao wrote:
> On Tue, Jul 09, 2019 at 05:49:16PM +0800, Kirti Wankhede 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.
>> - read data_size - amount of data in bytes written by vendor driver in 
>> migration
>>   region.
>> - if data section is trapped, pread() from data_offset of data_size.
>> - if data section is mmaped, read mmaped buffer of 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
>> c. read data_offset - indicates kernel driver to write data to staging
>>    buffer which is mmapped.
>> d. read data_size - amount of data in bytes written by vendor driver in
>>    migration region.
>> e. if data section is trapped, pread() from data_offset of data_size.
>> f. if data section is mmaped, read mmaped buffer of data_size.
>> g. Write data packet as below:
>>    {VFIO_MIG_FLAG_DEV_DATA_STATE, data_size, actual data}
>> h. iterate through steps b to g while (pending_bytes > 0)
>> i. Write {VFIO_MIG_FLAG_END_OF_STATE}
>>
>> When data region is mapped, its user's responsibility to read data from
>> data_offset of data_size before moving to next steps.
>>
>> .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.
>>
>> Signed-off-by: Kirti Wankhede <address@hidden>
>> Reviewed-by: Neo Jia <address@hidden>
>> ---
>>  hw/vfio/migration.c  | 246 
>> +++++++++++++++++++++++++++++++++++++++++++++++++++
>>  hw/vfio/trace-events |   6 ++
>>  2 files changed, 252 insertions(+)
>>
>> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
>> index 0597a45fda2d..4e9b4cce230b 100644
>> --- a/hw/vfio/migration.c
>> +++ b/hw/vfio/migration.c
>> @@ -117,6 +117,138 @@ static int vfio_migration_set_state(VFIODevice 
>> *vbasedev, uint32_t state)
>>      return 0;
>>  }
>>  
>> +static void *find_data_region(VFIORegion *region,
>> +                              uint64_t data_offset,
>> +                              uint64_t data_size)
>> +{
>> +    void *ptr = NULL;
>> +    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) 
>> &&
>> +            (data_size <= region->mmaps[i].size)) {
>> +            ptr = region->mmaps[i].mmap + (data_offset -
>> +                                           region->mmaps[i].offset);
>> +            break;
>> +        }
>> +    }
>> +    return ptr;
>> +}
>> +
>> +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("%s: Failed to get migration buffer data offset %d",
>> +                     vbasedev->name, 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("%s: Failed to get migration buffer data size %d",
>> +                     vbasedev->name, ret);
>> +        return -EINVAL;
>> +    }
>> +
>> +    if (data_size > 0) {
>> +        void *buf = NULL;
>> +        bool buffer_mmaped;
>> +
>> +        if (region->mmaps) {
>> +            buf = find_data_region(region, data_offset, data_size);
>> +        }
>> +
>> +        buffer_mmaped = (buf != NULL) ? true : false;
>> +
>> +        if (!buffer_mmaped) {
>> +            buf = g_try_malloc0(data_size);
>> +            if (!buf) {
>> +                error_report("%s: Error allocating buffer ", __func__);
>> +                return -ENOMEM;
>> +            }
>> +
>> +            ret = pread(vbasedev->fd, buf, data_size,
>> +                        region->fd_offset + data_offset);
>> +            if (ret != data_size) {
>> +                error_report("%s: Failed to get migration data %d",
>> +                             vbasedev->name, 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;
> This line "migration->pending_bytes -= data_size;" is not necessary, as
> it will be updated anyway in vfio_update_pending()
> 

Right, removing it.

Thanks,
Kirti