Re: [PATCH QEMU v25 07/17] vfio: Register SaveVMHandlers for VFIO device

[Kirti Wankhede]

On 6/23/2020 4:20 AM, Alex Williamson wrote:
> On Sun, 21 Jun 2020 01:51:16 +0530
> Kirti Wankhede <kwankhede@nvidia.com> wrote:
>
> > Define flags to be used as delimeter in migration file stream.
> > Added .save_setup and .save_cleanup functions. Mapped & unmapped migration
> > region from these functions at source during saving or pre-copy phase.
> > Set VFIO device state depending on VM's state. During live migration, VM is
> > running when .save_setup is called, _SAVING | _RUNNING state is set for VFIO
> > device. During save-restore, VM is paused, _SAVING state is set for VFIO device.
> >
> > Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> > Reviewed-by: Neo Jia <cjia@nvidia.com>
> > ---
> >   hw/vfio/migration.c  | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> >   hw/vfio/trace-events |  2 ++
> >   2 files changed, 94 insertions(+)
> >
> > diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> > index e30bd8768701..133bb5b1b3b2 100644
> > --- a/hw/vfio/migration.c
> > +++ b/hw/vfio/migration.c
> > @@ -8,12 +8,15 @@
> >    */
> >   
> >   #include "qemu/osdep.h"
> > +#include "qemu/main-loop.h"
> > +#include "qemu/cutils.h"
> >   #include <linux/vfio.h>
> >   
> >   #include "sysemu/runstate.h"
> >   #include "hw/vfio/vfio-common.h"
> >   #include "cpu.h"
> >   #include "migration/migration.h"
> > +#include "migration/vmstate.h"
> >   #include "migration/qemu-file.h"
> >   #include "migration/register.h"
> >   #include "migration/blocker.h"
> > @@ -24,6 +27,17 @@
> >   #include "pci.h"
> >   #include "trace.h"
> >   
> > +/*
> > + * Flags used as delimiter:
> > + * 0xffffffff => MSB 32-bit all 1s
> > + * 0xef10     => emulated (virtual) function IO
> > + * 0x0000     => 16-bits reserved for flags
> > + */
> > +#define VFIO_MIG_FLAG_END_OF_STATE      (0xffffffffef100001ULL)
> > +#define VFIO_MIG_FLAG_DEV_CONFIG_STATE  (0xffffffffef100002ULL)
> > +#define VFIO_MIG_FLAG_DEV_SETUP_STATE   (0xffffffffef100003ULL)
> > +#define VFIO_MIG_FLAG_DEV_DATA_STATE    (0xffffffffef100004ULL)
> > +
> >   static void vfio_migration_region_exit(VFIODevice *vbasedev)
> >   {
> >       VFIOMigration *migration = vbasedev->migration;
> > @@ -126,6 +140,65 @@ static int vfio_migration_set_state(VFIODevice *vbasedev, 
> > uint32_t mask,
> >       return 0;
> >   }
> >   
> > +/* ---------------------------------------------------------------------- */
> > +
> > +static int vfio_save_setup(QEMUFile *f, void *opaque)
> > +{
> > +    VFIODevice *vbasedev = opaque;
> > +    VFIOMigration *migration = vbasedev->migration;
> > +    int ret;
> > +
> > +    trace_vfio_save_setup(vbasedev->name);
> > +
> > +    qemu_put_be64(f, VFIO_MIG_FLAG_DEV_SETUP_STATE);
> > +
> > +    if (migration->region.mmaps) {
> > +        qemu_mutex_lock_iothread();
> > +        ret = vfio_region_mmap(&migration->region);
> > +        qemu_mutex_unlock_iothread();
> > +        if (ret) {
> > +            error_report("%s: Failed to mmap VFIO migration region %d: %s",
> > +                         vbasedev->name, migration->region.nr,
> > +                         strerror(-ret));
> > +            return ret;
>
> OTOH to my previous comments, this shouldn't be fatal, right?  mmaps
> are optional anyway so it should be sufficient to push an error report
> to explain why this might be slower than normal, but we can still
> proceed.

Right, defining region to be sparse mmap is optional.
migration->region.mmaps is set if vendor driver defines sparse mmapable 
regions and VFIO_REGION_INFO_FLAG_MMAP flag is set. If this flag is set 
then error on mmap() should be fatal.

If there is not mmapable region, then migration will proceed.

> > +        }
> > +    }
> > +
> > +    ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_MASK,
> > +                                   VFIO_DEVICE_STATE_SAVING);
> > +    if (ret) {
> > +        error_report("%s: Failed to set state SAVING", vbasedev->name);
> > +        return ret;
> > +    }
>
> We seem to be lacking support in the callers for detecting if the
> device is in an error state.  I'm not sure what our options are
> though, maybe only a hw_error().

Returning error here fails migration process. And if device is in error 
state, any application running inside VM using this device would fail.
I think, there is no need to take any special action here by detecting 
device error state.

> > +
> > +    qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
> > +
> > +    ret = qemu_file_get_error(f);
> > +    if (ret) {
> > +        return ret;
> > +    }
> > +
> > +    return 0;
> > +}
> > +
> > +static void vfio_save_cleanup(void *opaque)
> > +{
> > +    VFIODevice *vbasedev = opaque;
> > +    VFIOMigration *migration = vbasedev->migration;
> > +
> > +    if (migration->region.mmaps) {
> > +        vfio_region_unmap(&migration->region);
> > +    }
> > +    trace_vfio_save_cleanup(vbasedev->name);
> > +}
> > +
> > +static SaveVMHandlers savevm_vfio_handlers = {
> > +    .save_setup = vfio_save_setup,
> > +    .save_cleanup = vfio_save_cleanup,
> > +};
> > +
> > +/* ---------------------------------------------------------------------- */
> > +
> >   static void vfio_vmstate_change(void *opaque, int running, RunState state)
> >   {
> >       VFIODevice *vbasedev = opaque;
> > @@ -180,6 +253,7 @@ static int vfio_migration_init(VFIODevice *vbasedev,
> >                                  struct vfio_region_info *info)
> >   {
> >       int ret;
> > +    char id[256] = "";
> >   
> >       vbasedev->migration = g_new0(VFIOMigration, 1);
> >   
> > @@ -192,6 +266,24 @@ static int vfio_migration_init(VFIODevice *vbasedev,
> >           return ret;
> >       }
> >   
> > +    if (vbasedev->ops->vfio_get_object) {
>
> Nit, vfio_migration_region_init() would have failed already if this were
> not available.  Perhaps do the test once at the start of this function
> instead?  Thanks,

Ok, will do that.

Thanks,
Kirti


> Alex
>
> > +        Object *obj = vbasedev->ops->vfio_get_object(vbasedev);
> > +
> > +        if (obj) {
> > +            DeviceState *dev = DEVICE(obj);
> > +            char *oid = vmstate_if_get_id(VMSTATE_IF(dev));
> > +
> > +            if (oid) {
> > +                pstrcpy(id, sizeof(id), oid);
> > +                pstrcat(id, sizeof(id), "/");
> > +                g_free(oid);
> > +            }
> > +        }
> > +    }
> > +    pstrcat(id, sizeof(id), "vfio");
> > +
> > +    register_savevm_live(id, VMSTATE_INSTANCE_ID_ANY, 1, &savevm_vfio_handlers,
> > +                         vbasedev);
> >       vbasedev->vm_state = qemu_add_vm_change_state_handler(vfio_vmstate_change,
> >                                                             vbasedev);
> >       vbasedev->migration_state.notify = vfio_migration_state_notifier;
> > diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
> > index bd3d47b005cb..86c18def016e 100644
> > --- a/hw/vfio/trace-events
> > +++ b/hw/vfio/trace-events
> > @@ -149,3 +149,5 @@ vfio_migration_probe(const char *name, uint32_t index) " (%s) 
> > Region %d"
> >   vfio_migration_set_state(const char *name, uint32_t state) " (%s) state %d"
> >   vfio_vmstate_change(const char *name, int running, const char *reason, uint32_t 
> > dev_state) " (%s) running %d reason %s device state %d"
> >   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)"