Re: [PATCH QEMU v25 08/17] vfio: Add save state functions to SaveVMHandlers

[Alex Williamson <alex.williamson@redhat.com>]

On Sun, 21 Jun 2020 01:51:17 +0530
Kirti Wankhede <kwankhede@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. If pending_bytes > 0, go through below steps.
> - read data_offset - indicates kernel driver to write data to staging
>   buffer.
> - read data_size - amount of data in bytes written by vendor driver in
>   migration region.
> - read data_size bytes of data from data_offset in the migration region.
> - 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. If pending_bytes > 0, go through below steps.
> c. read data_offset - indicates kernel driver to write data to staging
>    buffer.
> d. read data_size - amount of data in bytes written by vendor driver in
>    migration region.
> e. read data_size bytes of data from data_offset in the migration region.
> f. Write data packet as below:
>    {VFIO_MIG_FLAG_DEV_DATA_STATE, data_size, actual data}
> g. iterate through steps b to f while (pending_bytes > 0)
> h. 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.
> 
> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> Reviewed-by: Neo Jia <cjia@nvidia.com>
> ---
>  hw/vfio/migration.c           | 283 ++++++++++++++++++++++++++++++++++++++++++
>  hw/vfio/trace-events          |   6 +
>  include/hw/vfio/vfio-common.h |   1 +
>  3 files changed, 290 insertions(+)
> 
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index 133bb5b1b3b2..ef1150c1ff02 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -140,6 +140,168 @@ static int vfio_migration_set_state(VFIODevice *vbasedev, uint32_t mask,
>      return 0;
>  }
>  
> +static void *get_data_section_size(VFIORegion *region, uint64_t data_offset,
> +                                   uint64_t data_size, uint64_t *size)
> +{
> +    void *ptr = NULL;
> +    int i;
> +
> +    if (!region->mmaps) {
> +        *size = data_size;
> +        return ptr;
> +    }
> +
> +    /* check if data_offset in within sparse mmap areas */
> +    for (i = 0; i < region->nr_mmaps; i++) {
> +        VFIOMmap *map = region->mmaps + i;
> +
> +        if ((data_offset >= map->offset) &&
> +            (data_offset < map->offset + map->size)) {
> +            ptr = map->mmap + data_offset - map->offset;
> +
> +            if (data_offset + data_size <= map->offset + map->size) {
> +                *size = data_size;
> +            } else {
> +                *size = map->offset + map->size - data_offset;
> +            }

Ultimately we take whichever result is smaller, so we could just use:

*size = MIN(data_size, map->offset + map->size - data_offset);

> +            break;
> +        }
> +    }
> +
> +    if (!ptr) {
> +        uint64_t limit = 0;
> +
> +        /*
> +         * data_offset is not within sparse mmap areas, find size of non-mapped
> +         * area. Check through all list since region->mmaps list is not sorted.
> +         */
> +        for (i = 0; i < region->nr_mmaps; i++) {
> +            VFIOMmap *map = region->mmaps + i;
> +
> +            if ((data_offset < map->offset) &&
> +                (!limit || limit > map->offset)) {
> +                limit = map->offset;
> +            }

We could have done this in an else branch of the previous loop to avoid
walking the entries twice.

> +        }
> +
> +        *size = limit ? limit - data_offset : data_size;
> +    }
> +    return ptr;
> +}
> +
> +static int vfio_save_buffer(QEMUFile *f, VFIODevice *vbasedev)
> +{
> +    VFIOMigration *migration = vbasedev->migration;
> +    VFIORegion *region = &migration->region;
> +    uint64_t data_offset = 0, data_size = 0, size;
> +    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;
> +    }
> +
> +    trace_vfio_save_buffer(vbasedev->name, data_offset, data_size,
> +                           migration->pending_bytes);
> +
> +    qemu_put_be64(f, data_size);
> +    size = data_size;
> +
> +    while (size) {
> +        void *buf = NULL;
> +        bool buffer_mmaped;
> +        uint64_t sec_size;
> +
> +        buf = get_data_section_size(region, data_offset, size, &sec_size);
> +
> +        buffer_mmaped = (buf != NULL);
> +
> +        if (!buffer_mmaped) {
> +            buf = g_try_malloc(sec_size);
> +            if (!buf) {
> +                error_report("%s: Error allocating buffer ", __func__);
> +                return -ENOMEM;
> +            }
> +
> +            ret = pread(vbasedev->fd, buf, sec_size,
> +                        region->fd_offset + data_offset);

Is the trade-off to allocate this buffer worth it?  I'd be tempted to
iterate with a basic data type here to avoid what could potentially be
a large memory allocation above.  It feels a little more robust, if not
perhaps as fast, but I this will mostly be a fallback or only cover
small ranges in normal operation.  Of course the data stream needs to
be compatible either way we retrieve it.

> +            if (ret != sec_size) {
> +                error_report("%s: Failed to get migration data %d",
> +                             vbasedev->name, ret);
> +                g_free(buf);
> +                return -EINVAL;
> +            }
> +        }
> +
> +        qemu_put_buffer(f, buf, sec_size);
> +
> +        if (!buffer_mmaped) {
> +            g_free(buf);
> +        }
> +        size -= sec_size;
> +        data_offset += sec_size;
> +    }
> +
> +    ret = qemu_file_get_error(f);
> +    if (ret) {
> +        return ret;
> +    }
> +
> +    return data_size;

This function returns int, data_size is uint64_t.  Thanks,

Alex

> +}
> +
> +static int vfio_update_pending(VFIODevice *vbasedev)
> +{
> +    VFIOMigration *migration = vbasedev->migration;
> +    VFIORegion *region = &migration->region;
> +    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));
> +    if ((ret < 0) || (ret != sizeof(pending_bytes))) {
> +        error_report("%s: Failed to get pending bytes %d",
> +                     vbasedev->name, ret);
> +        migration->pending_bytes = 0;
> +        return (ret < 0) ? ret : -EINVAL;
> +    }
> +
> +    migration->pending_bytes = pending_bytes;
> +    trace_vfio_update_pending(vbasedev->name, 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->ops && vbasedev->ops->vfio_save_config) {
> +        vbasedev->ops->vfio_save_config(vbasedev, f);
> +    }
> +
> +    qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
> +
> +    trace_vfio_save_device_config_state(vbasedev->name);
> +
> +    return qemu_file_get_error(f);
> +}
> +
>  /* ---------------------------------------------------------------------- */
>  
>  static int vfio_save_setup(QEMUFile *f, void *opaque)
> @@ -192,9 +354,130 @@ static void vfio_save_cleanup(void *opaque)
>      trace_vfio_save_cleanup(vbasedev->name);
>  }
>  
> +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;
> +    }
> +
> +    *res_precopy_only += migration->pending_bytes;
> +
> +    trace_vfio_save_pending(vbasedev->name, *res_precopy_only,
> +                            *res_postcopy_only, *res_compatible);
> +}
> +
> +static int vfio_save_iterate(QEMUFile *f, void *opaque)
> +{
> +    VFIODevice *vbasedev = opaque;
> +    VFIOMigration *migration = vbasedev->migration;
> +    int ret, data_size;
> +
> +    qemu_put_be64(f, VFIO_MIG_FLAG_DEV_DATA_STATE);
> +
> +    if (migration->pending_bytes == 0) {
> +        ret = vfio_update_pending(vbasedev);
> +        if (ret) {
> +            return ret;
> +        }
> +
> +        if (migration->pending_bytes == 0) {
> +            /* indicates data finished, goto complete phase */
> +            return 1;
> +        }
> +    }
> +
> +    data_size = vfio_save_buffer(f, vbasedev);
> +
> +    if (data_size < 0) {
> +        error_report("%s: vfio_save_buffer failed %s", vbasedev->name,
> +                     strerror(errno));
> +        return data_size;
> +    }
> +
> +    qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
> +
> +    ret = qemu_file_get_error(f);
> +    if (ret) {
> +        return ret;
> +    }
> +
> +    trace_vfio_save_iterate(vbasedev->name, data_size);
> +
> +    return 0;
> +}
> +
> +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_RUNNING,
> +                                   VFIO_DEVICE_STATE_SAVING);
> +    if (ret) {
> +        error_report("%s: Failed to set state STOP and SAVING",
> +                     vbasedev->name);
> +        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("%s: Failed to save buffer", vbasedev->name);
> +            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_SAVING, 0);
> +    if (ret) {
> +        error_report("%s: Failed to set state STOPPED", vbasedev->name);
> +        return ret;
> +    }
> +
> +    trace_vfio_save_complete_precopy(vbasedev->name);
> +    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,
>  };
>  
>  /* ---------------------------------------------------------------------- */
> diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
> index 86c18def016e..9a1c5e17d97f 100644
> --- a/hw/vfio/trace-events
> +++ b/hw/vfio/trace-events
> @@ -151,3 +151,9 @@ vfio_vmstate_change(const char *name, int running, const char *reason, uint32_t
>  vfio_migration_state_notifier(const char *name, const char *state) " (%s) state %s"
>  vfio_save_setup(const char *name) " (%s)"
>  vfio_save_cleanup(const char *name) " (%s)"
> +vfio_save_buffer(const char *name, uint64_t data_offset, uint64_t data_size, uint64_t pending) " (%s) Offset 0x%"PRIx64" size 0x%"PRIx64" pending 0x%"PRIx64
> +vfio_update_pending(const char *name, uint64_t pending) " (%s) pending 0x%"PRIx64
> +vfio_save_device_config_state(const char *name) " (%s)"
> +vfio_save_pending(const char *name, uint64_t precopy, uint64_t postcopy, uint64_t compatible) " (%s) precopy 0x%"PRIx64" postcopy 0x%"PRIx64" compatible 0x%"PRIx64
> +vfio_save_iterate(const char *name, int data_size) " (%s) data_size %d"
> +vfio_save_complete_precopy(const char *name) " (%s)"
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index 28f55f66d019..c78033e4149d 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -60,6 +60,7 @@ typedef struct VFIORegion {
>  
>  typedef struct VFIOMigration {
>      VFIORegion region;
> +    uint64_t pending_bytes;
>  } VFIOMigration;
>  
>  typedef struct VFIOAddressSpace {