[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PATCH v26 09/17] vfio: Add load state functions to SaveVMHandlers
From: |
Cornelia Huck |
Subject: |
Re: [PATCH v26 09/17] vfio: Add load state functions to SaveVMHandlers |
Date: |
Tue, 20 Oct 2020 18:25:32 +0200 |
On Mon, 19 Oct 2020 02:17:43 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:
> On 10/1/2020 3:37 PM, Cornelia Huck wrote:
> > On Wed, 23 Sep 2020 04:54:11 +0530
> > Kirti Wankhede <kwankhede@nvidia.com> wrote:
> >
> >> Sequence during _RESUMING device state:
> >> While data for this device is available, repeat below steps:
> >> a. read data_offset from where user application should write data.
> >> b. write data of data_size to migration region from data_offset.
> >> c. write data_size which indicates vendor driver that data is written in
> >> staging buffer.
> >>
> >> For user, data is opaque. User should write data in the same order as
> >> received.
> >>
> >> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> >> Reviewed-by: Neo Jia <cjia@nvidia.com>
> >> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> >> ---
> >> hw/vfio/migration.c | 170
> >> +++++++++++++++++++++++++++++++++++++++++++++++++++
> >> hw/vfio/trace-events | 3 +
> >> 2 files changed, 173 insertions(+)
> >>
> >> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> >> index 4611bb972228..ffd70282dd0e 100644
> >> --- a/hw/vfio/migration.c
> >> +++ b/hw/vfio/migration.c
> >> @@ -328,6 +328,33 @@ static int vfio_save_device_config_state(QEMUFile *f,
> >> void *opaque)
> >> return qemu_file_get_error(f);
> >> }
> >>
> >> +static int vfio_load_device_config_state(QEMUFile *f, void *opaque)
> >> +{
> >> + VFIODevice *vbasedev = opaque;
> >> + uint64_t data;
> >> +
> >> + if (vbasedev->ops && vbasedev->ops->vfio_load_config) {
> >> + int ret;
> >> +
> >> + ret = vbasedev->ops->vfio_load_config(vbasedev, f);
> >> + if (ret) {
> >> + error_report("%s: Failed to load device config space",
> >> + vbasedev->name);
> >> + return ret;
> >> + }
> >> + }
> >> +
> >> + data = qemu_get_be64(f);
> >> + if (data != VFIO_MIG_FLAG_END_OF_STATE) {
> >> + error_report("%s: Failed loading device config space, "
> >> + "end flag incorrect 0x%"PRIx64, vbasedev->name,
> >> data);
> >
> > I'm confused here: If we don't have a vfio_load_config callback, or if
> > that callback did not read everything, we also might end up with a
> > value that's not END_OF_STATE... in that case, the problem is not with
> > the stream, but rather with the consumer?
>
> Right, hence "end flag incorrect" is reported.
Yes, but that's what I find confusing... a missing or incorrect
vfio_load_config callback does not have anything to do with incorrect
end flags as present in the stream, but with the consumer not reading
things correctly. If I got this error, I would go looking whether
there's anything wrong with the stream and the code that produced it,
and that's the wrong direction.
(...)
> >> +static int vfio_load_state(QEMUFile *f, void *opaque, int version_id)
> >> +{
> >> + VFIODevice *vbasedev = opaque;
> >> + VFIOMigration *migration = vbasedev->migration;
> >> + int ret = 0;
> >> + uint64_t data, data_size;
> >> +
> >> + data = qemu_get_be64(f);
> >> + while (data != VFIO_MIG_FLAG_END_OF_STATE) {
> >> +
> >> + trace_vfio_load_state(vbasedev->name, data);
> >> +
> >> + switch (data) {
> >> + case VFIO_MIG_FLAG_DEV_CONFIG_STATE:
> >> + {
> >> + ret = vfio_load_device_config_state(f, opaque);
> >> + if (ret) {
> >> + return ret;
> >> + }
> >> + break;
> >> + }
> >> + case VFIO_MIG_FLAG_DEV_SETUP_STATE:
> >> + {
> >> + data = qemu_get_be64(f);
> >> + if (data == VFIO_MIG_FLAG_END_OF_STATE) {
> >> + return ret;
> >> + } else {
> >> + error_report("%s: SETUP STATE: EOS not found 0x%"PRIx64,
> >> + vbasedev->name, data);
> >> + return -EINVAL;
> >> + }
> >> + break;
> >> + }
> >> + case VFIO_MIG_FLAG_DEV_DATA_STATE:
> >> + {
> >> + VFIORegion *region = &migration->region;
> >> + uint64_t data_offset = 0, size;
> >
> > I think this function would benefit from splitting this off into a
> > function handling DEV_DATA_STATE. It is quite hard to follow through
> > all the checks and find out when we continue, and when we break off.
> >
>
> Each switch case has a break, we break off on success cases, where as we
> return error if we encounter any case where (ret < 0)
Of course, but I don't find it easy to follow when the errors are
happening.
>
>
> > Some documentation about the markers would also be really helpful.
>
> Sure adding it in patch 07, where these are defined.
>
> > The logic seems to be:
> > - DEV_CONFIG_STATE has config data and must be ended by END_OF_STATE
> Right
>
> > - DEV_SETUP_STATE has only END_OF_STATE, no data
> Right now there is no data, but this is provision to add data if
> required in future.
>
> > - DEV_DATA_STATE has... data; if there's any END_OF_STATE, it's buried
> > far down in the called functions
> >
>
> This is not correct, END_OF_STATE is after data. Moved data buffer
> loading logic to function vfio_load_buffer(), so DEV_DATA_STATE looks
> simplified as below. Hope this helps.
>
> case VFIO_MIG_FLAG_DEV_DATA_STATE:
> {
> uint64_t data_size;
>
> data_size = qemu_get_be64(f);
> if (data_size == 0) {
> break;
> }
>
> ret = vfio_load_buffer(f, vbasedev, data_size);
> if (ret < 0) {
> return ret;
> }
> break;
> }
Hm.
What I find not that easy to follow is the structure here:
while (!end_marker) {
switch (data) {
case config_state:
if (load_config)
return error;
break;
case setup_state:
read_next_value();
if (end_marker)
return 0;
else
return error;
break;
case data_state:
size = read_next_value();
if (!size)
break;
if (vfio_load_buffer())
return error;
break;
default:
return error;
}
read_next_value();
if (qemu_file_get_error())
return error;
}
So, what I don't understand is:
- Why do we call qemu_file_get_error() only after we went through the
whole switch? This means it is never called for the
setup_state/end_marker pair.
- If we look for an end marker for config_state and data_state, it's
buried in the called functions. How can we be sure they actually do
look for it? That needs at least a comment.
- If we find a valid setup_state section, we return success
immediately. If we find valid config_state or data_state sections, we
keep looking for more sections. Why? This also needs at least a
comment.
>
> Also handling the case if data_size is greater than the data section of
> migration region at destination in vfio_load_buffer()in my next version.
>
> Thanks,
> Kirti
>
> >
> >> +
> >> + data_size = size = qemu_get_be64(f);
> >> + if (data_size == 0) {
> >> + break;
> >> + }
> >> +
> >> + ret = vfio_mig_read(vbasedev, &data_offset,
> >> sizeof(data_offset),
> >> + region->fd_offset +
> >> + offsetof(struct
> >> vfio_device_migration_info,
> >> + data_offset));
> >> + if (ret < 0) {
> >> + return ret;
> >> + }
> >> +
> >> + trace_vfio_load_state_device_data(vbasedev->name, data_offset,
> >> + data_size);
> >> +
> >> + while (size) {
> >> + void *buf = NULL;
> >> + uint64_t sec_size;
> >> + bool buf_alloc = false;
> >> +
> >> + buf = get_data_section_size(region, data_offset, size,
> >> + &sec_size);
> >> +
> >> + if (!buf) {
> >> + buf = g_try_malloc(sec_size);
> >> + if (!buf) {
> >> + error_report("%s: Error allocating buffer ",
> >> __func__);
> >> + return -ENOMEM;
> >> + }
> >> + buf_alloc = true;
> >> + }
> >> +
> >> + qemu_get_buffer(f, buf, sec_size);
> >> +
> >> + if (buf_alloc) {
> >> + ret = vfio_mig_write(vbasedev, buf, sec_size,
> >> + region->fd_offset + data_offset);
> >> + g_free(buf);
> >> +
> >> + if (ret < 0) {
> >> + return ret;
> >> + }
> >> + }
> >> + size -= sec_size;
> >> + data_offset += sec_size;
> >> + }
> >> +
> >> + ret = vfio_mig_write(vbasedev, &data_size, sizeof(data_size),
> >> + region->fd_offset +
> >> + offsetof(struct vfio_device_migration_info,
> >> data_size));
> >> + if (ret < 0) {
> >> + return ret;
> >> + }
> >> + break;
> >> + }
> >> +
> >> + default:
> >> + error_report("%s: Unknown tag 0x%"PRIx64, vbasedev->name,
> >> data);
> >> + return -EINVAL;
> >> + }
> >> +
> >> + data = qemu_get_be64(f);
> >> + ret = qemu_file_get_error(f);
> >> + if (ret) {
> >> + return ret;
> >> + }
> >> + }
> >> +
> >> + return ret;
> >> +}
> >> +