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

[Alex Williamson]

On Sun, 18 Oct 2020 02:00:44 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:

> 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.

But these are only valid when migration is supported and thus when
VFIOMigration exists.  Thanks,

Alex