Re: [Qemu-devel] [RFC PATCH V4 1/4] vfio: introduce a new VFIO subregion for mdev device migration support

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

On Mon, 16 Apr 2018 20:14:03 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:

> On 4/10/2018 11:32 AM, Yulei Zhang wrote:
> > New VFIO sub region VFIO_REGION_SUBTYPE_DEVICE_STATE is added
> > to fetch and restore the status of mdev device vGPU during the
> > live migration.
> > 
> > Signed-off-by: Yulei Zhang <yulei.zhang@intel.com>
> > ---
> >  hw/vfio/pci.c              | 25 ++++++++++++++++++++++++-
> >  hw/vfio/pci.h              |  2 ++
> >  linux-headers/linux/vfio.h |  9 ++++++---
> >  3 files changed, 32 insertions(+), 4 deletions(-)
> > 
> > diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> > index c977ee3..f98a9dd 100644
> > --- a/hw/vfio/pci.c
> > +++ b/hw/vfio/pci.c
> > @@ -32,6 +32,7 @@
> >  #include "pci.h"
> >  #include "trace.h"
> >  #include "qapi/error.h"
> > +#include "migration/blocker.h"
> >  
> >  #define MSIX_CAP_LENGTH 12
> >  
> > @@ -2821,6 +2822,25 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
> >          vfio_vga_quirk_setup(vdev);
> >      }
> >  
> > +    struct vfio_region_info *device_state;
> > +    /* device state region setup */
> > +    if (!vfio_get_dev_region_info(&vdev->vbasedev,
> > +                VFIO_REGION_TYPE_PCI_VENDOR_TYPE,

This is not how VENDOR_TYPE is meant to be used.  We have a 32-bit type
and 32-bit sub-type.  When bit 31 of type is set (ie. VENDOR_TYPE),
then the low 16-bits (VENDOR_MASK) defines a vendor specific set of
sub-types.  Using it as above, you're stomping on vendor 0x0000's
vendor sub-types.  I would expect non-vendor specific types to leave
bit 31 of the type field clear.  We could then define a universal type
for device state with a sub-type specifying the API such that we could
revise the API by providing an updated sub-type.  Or perhaps there are
devices that want separate save vs restore regions, we could do that
with the sub-type.

> > +                VFIO_REGION_SUBTYPE_DEVICE_STATE, &device_state)) {
> > +        memcpy(&vdev->device_state, device_state,
> > +               sizeof(struct vfio_region_info));
> > +        g_free(device_state);
> > +    } else {
> > +        error_setg(&vdev->migration_blocker,
> > +                "Migration disabled: cannot support device state region");
> > +        migrate_add_blocker(vdev->migration_blocker, &err);

This appears as if it's going to be rather verbose and generate errors
for anything not supporting migration, which is currently everything.
Maybe there should be an OnOffAuto vfio-pci device option for the user
to specify migration such that if migration=on is specified the device
will fail if it's not available.  Otherwise the default would be auto.

> > +        if (err) {
> > +            error_propagate(errp, err);
> > +            error_free(vdev->migration_blocker);
> > +            goto error;
> > +        }
> > +    }
> > +  
> 
> I think there should be a _PROBE ioctl before trying to setup region for
> migration. If vfio device driver or vendor driver for mdev device
> supports migration capability, _PROBE ioctl should return success along
> with region's information <index, size> which can be used to setup the
> region.

How is _PROBE different from _REGION_INFO which already exists to tell
us information about the region?

> >      for (i = 0; i < PCI_ROM_SLOT; i++) {
> >          vfio_bar_quirk_setup(vdev, i);
> >      }
> > @@ -2884,6 +2904,10 @@ out_teardown:
> >      vfio_teardown_msi(vdev);
> >      vfio_bars_exit(vdev);
> >  error:
> > +    if (vdev->migration_blocker) {
> > +        migrate_del_blocker(vdev->migration_blocker);
> > +        error_free(vdev->migration_blocker);
> > +    }
> >      error_prepend(errp, ERR_PREFIX, vdev->vbasedev.name);
> >  }
> >  
> > @@ -3009,7 +3033,6 @@ static Property vfio_pci_dev_properties[] = {
> >  
> >  static const VMStateDescription vfio_pci_vmstate = {
> >      .name = "vfio-pci",
> > -    .unmigratable = 1,  
> 
> Based on the result of above _PROBE ioctl, 'unmigratable' should be set
> if vendor driver doesn't support migration capability.

.unmigratable isn't really dynamically settable aiui, thus the
existence of the migration blocker.

> >  };
> >  
> >  static void vfio_pci_dev_class_init(ObjectClass *klass, void *data)
> > diff --git a/hw/vfio/pci.h b/hw/vfio/pci.h
> > index 502a575..0ee1724 100644
> > --- a/hw/vfio/pci.h
> > +++ b/hw/vfio/pci.h
> > @@ -116,6 +116,8 @@ typedef struct VFIOPCIDevice {
> >      VFIOBAR bars[PCI_NUM_REGIONS - 1]; /* No ROM */
> >      VFIOVGA *vga; /* 0xa0000, 0x3b0, 0x3c0 */
> >      void *igd_opregion;
> > +    struct vfio_region_info device_state;
> > +    Error *migration_blocker;
> >      PCIHostDeviceAddress host;
> >      EventNotifier err_notifier;
> >      EventNotifier req_notifier;
> > diff --git a/linux-headers/linux/vfio.h b/linux-headers/linux/vfio.h
> > index 4312e96..e3380ad 100644
> > --- a/linux-headers/linux/vfio.h
> > +++ b/linux-headers/linux/vfio.h
> > @@ -297,9 +297,12 @@ struct vfio_region_info_cap_type {
> >  #define VFIO_REGION_TYPE_PCI_VENDOR_MASK	(0xffff)
> >  
> >  /* 8086 Vendor sub-types */
> > -#define VFIO_REGION_SUBTYPE_INTEL_IGD_OPREGION	(1)
> > -#define VFIO_REGION_SUBTYPE_INTEL_IGD_HOST_CFG	(2)
> > -#define VFIO_REGION_SUBTYPE_INTEL_IGD_LPC_CFG	(3)
> > +#define VFIO_REGION_SUBTYPE_INTEL_IGD_OPREGION		(1)
> > +#define VFIO_REGION_SUBTYPE_INTEL_IGD_HOST_CFG		(2)
> > +#define VFIO_REGION_SUBTYPE_INTEL_IGD_LPC_CFG		(3)
> > +
> > +/* Mdev sub-type for device state save and restore */
> > +#define VFIO_REGION_SUBTYPE_DEVICE_STATE	(4)

This continues on with the 0x8086 vendor sub-types, which is entirely
unnecessary as each vendor has an entire sub-type address space and we
shouldn't be using a vendor type anyway.  Additionally, we need
significantly more documentation on the API for this region.  Thanks,

Alex

> >  
> >  /**
> >   * VFIO_DEVICE_GET_IRQ_INFO - _IOWR(VFIO_TYPE, VFIO_BASE + 9,
> >