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

From: Alex Williamson <alex.williamson@redhat.com>
To: Kirti Wankhede <kwankhede@nvidia.com>
Cc: cohuck@redhat.com, cjia@nvidia.com, aik@ozlabs.ru,
	Zhengxiao.zx@Alibaba-inc.com, shuangtai.tst@alibaba-inc.com,
	qemu-devel@nongnu.org, peterx@redhat.com, eauger@redhat.com,
	yi.l.liu@intel.com, quintela@redhat.com, ziye.yang@intel.com,
	armbru@redhat.com, mlevitsk@redhat.com, pasic@linux.ibm.com,
	felipe@nutanix.com, zhi.a.wang@intel.com, kevin.tian@intel.com,
	yan.y.zhao@intel.com, dgilbert@redhat.com,
	changpeng.liu@intel.com, eskultet@redhat.com, Ken.Xue@amd.com,
	jonathan.davies@nutanix.com, pbonzini@redhat.com
Subject: Re: [PATCH v26 05/17] vfio: Add VM state change handler to know state of VM
Date: Fri, 25 Sep 2020 14:20:23 -0600	[thread overview]
Message-ID: <20200925142023.54e2c7c0@x1.home> (raw)
In-Reply-To: <1600817059-26721-6-git-send-email-kwankhede@nvidia.com>

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.

> +        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.

> +
> +    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?

> +        }
> +
> +        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.

> +}
> +
> +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.

> +        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,

Alex

>  } VFIODevice;
>  
>  struct VFIODeviceOps {