Re: [PATCH v26 05/17] vfio: Add VM state change handler to know state of VM

[Kirti Wankhede]

On 9/26/2020 1:50 AM, Alex Williamson wrote:
> On Wed, 23 Sep 2020 04:54:07 +0530
> Kirti Wankhede <kwankhede@nvidia.com> wrote:
>
> > VM state change handler gets called on change in VM's state. This is used to set
> > VFIO device state to _RUNNING.
> >
> > 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           | 136 ++++++++++++++++++++++++++++++++++++++++++
> >   hw/vfio/trace-events          |   3 +-
> >   include/hw/vfio/vfio-common.h |   4 ++
> >   3 files changed, 142 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> > index 2f760f1f9c47..a30d628ba963 100644
> > --- a/hw/vfio/migration.c
> > +++ b/hw/vfio/migration.c
> > @@ -10,6 +10,7 @@
> >   #include "qemu/osdep.h"
> >   #include <linux/vfio.h>
> >   
> > +#include "sysemu/runstate.h"
> >   #include "hw/vfio/vfio-common.h"
> >   #include "cpu.h"
> >   #include "migration/migration.h"
> > @@ -22,6 +23,58 @@
> >   #include "exec/ram_addr.h"
> >   #include "pci.h"
> >   #include "trace.h"
> > +#include "hw/hw.h"
> > +
> > +static inline int vfio_mig_access(VFIODevice *vbasedev, void *val, int count,
> > +                                  off_t off, bool iswrite)
> > +{
> > +    int ret;
> > +
> > +    ret = iswrite ? pwrite(vbasedev->fd, val, count, off) :
> > +                    pread(vbasedev->fd, val, count, off);
> > +    if (ret < count) {
> > +        error_report("vfio_mig_%s%d %s: failed at offset 0x%lx, err: %s",
> > +                     iswrite ? "write" : "read", count * 8,
> > +                     vbasedev->name, off, strerror(errno));
>
> This would suggest from the log that there's, for example, a
> vfio_mig_read8 function, which doesn't exist.

Changing to:
error_report("vfio_mig_%s %d byte %s: failed at offset 0x%lx, err: %s",
             iswrite ? "write" : "read", count,
             vbasedev->name, off, strerror(errno));
Hope this address your concern.

> > +        return (ret < 0) ? ret : -EINVAL;
> > +    }
> > +    return 0;
> > +}
> > +
> > +static int vfio_mig_rw(VFIODevice *vbasedev, __u8 *buf, size_t count,
> > +                       off_t off, bool iswrite)
> > +{
> > +    int ret, done = 0;
> > +    __u8 *tbuf = buf;
> > +
> > +    while (count) {
> > +        int bytes = 0;
> > +
> > +        if (count >= 8 && !(off % 8)) {
> > +            bytes = 8;
> > +        } else if (count >= 4 && !(off % 4)) {
> > +            bytes = 4;
> > +        } else if (count >= 2 && !(off % 2)) {
> > +            bytes = 2;
> > +        } else {
> > +            bytes = 1;
> > +        }
> > +
> > +        ret = vfio_mig_access(vbasedev, tbuf, bytes, off, iswrite);
> > +        if (ret) {
> > +            return ret;
> > +        }
> > +
> > +        count -= bytes;
> > +        done += bytes;
> > +        off += bytes;
> > +        tbuf += bytes;
> > +    }
> > +    return done;
> > +}
> > +
> > +#define vfio_mig_read(f, v, c, o)       vfio_mig_rw(f, (__u8 *)v, c, o, false)
> > +#define vfio_mig_write(f, v, c, o)      vfio_mig_rw(f, (__u8 *)v, c, o, true)
> >   
> >   static void vfio_migration_region_exit(VFIODevice *vbasedev)
> >   {
> > @@ -70,6 +123,82 @@ err:
> >       return ret;
> >   }
> >   
> > +static int vfio_migration_set_state(VFIODevice *vbasedev, uint32_t mask,
> > +                                    uint32_t value)
> > +{
> > +    VFIOMigration *migration = vbasedev->migration;
> > +    VFIORegion *region = &migration->region;
> > +    off_t dev_state_off = region->fd_offset +
> > +                      offsetof(struct vfio_device_migration_info, 
> > device_state);
> > +    uint32_t device_state;
> > +    int ret;
> > +
> > +    ret = vfio_mig_read(vbasedev, &device_state, sizeof(device_state),
> > +                        dev_state_off);
> > +    if (ret < 0) {
> > +        return ret;
> > +    }
> > +
> > +    device_state = (device_state & mask) | value;
>
> Agree with Connie that mask and value args are not immediately obvious
> how they're used.  I don't have a naming convention that would be more
> clear and the names do make some sense once they're understood, but a
> comment to indicate mask bits are preserved, value bits are set,
> remaining bits are cleared would probably help the reader.

Added comment.

> > +
> > +    if (!VFIO_DEVICE_STATE_VALID(device_state)) {
> > +        return -EINVAL;
> > +    }
> > +
> > +    ret = vfio_mig_write(vbasedev, &device_state, sizeof(device_state),
> > +                         dev_state_off);
> > +    if (ret < 0) {
> > +        ret = vfio_mig_read(vbasedev, &device_state, sizeof(device_state),
> > +                          dev_state_off);
> > +        if (ret < 0) {
> > +            return ret;
>
> Seems like we're in pretty bad shape here, should this be combined with
> below to trigger a hw_error?

Ok.

> > +        }
> > +
> > +        if (VFIO_DEVICE_STATE_IS_ERROR(device_state)) {
> > +            hw_error("%s: Device is in error state 0x%x",
> > +                     vbasedev->name, device_state);
> > +            return -EFAULT;
> > +        }
> > +    }
> > +
> > +    vbasedev->device_state = device_state;
> > +    trace_vfio_migration_set_state(vbasedev->name, device_state);
> > +    return 0;
>
> So we return success even if we failed to write the desired state as
> long as we were able to read back any non-error state?
> vbasedev->device_state remains correct, but it seems confusing form a
> caller perspective that a set-state can succeed but it's then necessary
> to check the state.

Correcting here. If vfio_mig_write() had retured error, return error 
from vfio_migration_set_state()

> > +}
> > +
> > +static void vfio_vmstate_change(void *opaque, int running, RunState state)
> > +{
> > +    VFIODevice *vbasedev = opaque;
> > +
> > +    if ((vbasedev->vm_running != running)) {
> > +        int ret;
> > +        uint32_t value = 0, mask = 0;
> > +
> > +        if (running) {
> > +            value = VFIO_DEVICE_STATE_RUNNING;
> > +            if (vbasedev->device_state & VFIO_DEVICE_STATE_RESUMING) {
> > +                mask = ~VFIO_DEVICE_STATE_RESUMING;
> > +            }
> > +        } else {
> > +            mask = ~VFIO_DEVICE_STATE_RUNNING;
> > +        }
> > +
> > +        ret = vfio_migration_set_state(vbasedev, mask, value);
> > +        if (ret) {
> > +            /*
> > +             * vm_state_notify() doesn't support reporting failure. If such
> > +             * error reporting support added in furure, migration should be
> > +             * aborted.
> > +             */
> > +            error_report("%s: Failed to set device state 0x%x",
> > +                         vbasedev->name, value & mask);
> > +        }
>
> Here for instance we assume that success means the device is now in the
> desired state, but we'd actually need to evaluate
> vbasedev->device_state to determine that.

Updating.

> > +        vbasedev->vm_running = running;
> > +        trace_vfio_vmstate_change(vbasedev->name, running, RunState_str(state),
> > +                                  value & mask);
> > +    }
> > +}
> > +
> >   static int vfio_migration_init(VFIODevice *vbasedev,
> >                                  struct vfio_region_info *info)
> >   {
> > @@ -87,8 +216,11 @@ static int vfio_migration_init(VFIODevice *vbasedev,
> >                        vbasedev->name);
> >           g_free(vbasedev->migration);
> >           vbasedev->migration = NULL;
> > +        return ret;
> >       }
> >   
> > +    vbasedev->vm_state = qemu_add_vm_change_state_handler(vfio_vmstate_change,
> > +                                                          vbasedev);
> >       return ret;
> >   }
> >   
> > @@ -131,6 +263,10 @@ add_blocker:
> >   
> >   void vfio_migration_finalize(VFIODevice *vbasedev)
> >   {
> > +    if (vbasedev->vm_state) {
> > +        qemu_del_vm_change_state_handler(vbasedev->vm_state);
> > +    }
> > +
> >       if (vbasedev->migration_blocker) {
> >           migrate_del_blocker(vbasedev->migration_blocker);
> >           error_free(vbasedev->migration_blocker);
> > diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
> > index 8fe913175d85..6524734bf7b4 100644
> > --- a/hw/vfio/trace-events
> > +++ b/hw/vfio/trace-events
> > @@ -149,4 +149,5 @@ vfio_display_edid_write_error(void) ""
> >   
> >   # migration.c
> >   vfio_migration_probe(const char *name, uint32_t index) " (%s) Region %d"
> > -
> > +vfio_migration_set_state(char *name, uint32_t state) " (%s) state %d"
> > +vfio_vmstate_change(char *name, int running, const char *reason, uint32_t dev_state) 
> > " (%s) running %d reason %s device state %d"
> > diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> > index 8275c4c68f45..25e3b1a3b90a 100644
> > --- a/include/hw/vfio/vfio-common.h
> > +++ b/include/hw/vfio/vfio-common.h
> > @@ -29,6 +29,7 @@
> >   #ifdef CONFIG_LINUX
> >   #include <linux/vfio.h>
> >   #endif
> > +#include "sysemu/sysemu.h"
> >   
> >   #define VFIO_MSG_PREFIX "vfio %s: "
> >   
> > @@ -119,6 +120,9 @@ typedef struct VFIODevice {
> >       unsigned int flags;
> >       VFIOMigration *migration;
> >       Error *migration_blocker;
> > +    VMChangeStateEntry *vm_state;
> > +    uint32_t device_state;
> > +    int vm_running;
>
> Could these be placed in VFIOMigration?  Thanks,

I think device_state should be part of VFIODevice since its about device 
rather than only related to migration, others can be moved to VFIOMigration.

Thanks,
Kirti


> Alex
>
> >   } VFIODevice;
> >   
> >   struct VFIODeviceOps {