[PATCH] hw/virtio: Fix the de-initialization of vhost-user devices

[PATCH] hw/virtio: Fix the de-initialization of vhost-user devices

[Thomas Huth]

The unrealize functions of the various vhost-user devices are
calling the corresponding vhost_*_set_status() functions with a
status of 0 to shut down the device correctly.

Now these vhost_*_set_status() functions all follow this scheme:

    bool should_start = virtio_device_should_start(vdev, status);

    if (vhost_dev_is_started(&vvc->vhost_dev) == should_start) {
        return;
    }

    if (should_start) {
        /* ... do the initialization stuff ... */
    } else {
        /* ... do the cleanup stuff ... */
    }

The problem here is virtio_device_should_start(vdev, 0) currently
always returns "true" since it internally only looks at vdev->started
instead of looking at the "status" parameter. Thus once the device
got started once, virtio_device_should_start() always returns true
and thus the vhost_*_set_status() functions return early, without
ever doing any clean-up when being called with status == 0. This
causes e.g. problems when trying to hot-plug and hot-unplug a vhost
user devices multiple times since the de-initialization step is
completely skipped during the unplug operation.

This bug has been introduced in commit 9f6bcfd99f ("hw/virtio: move
vm_running check to virtio_device_started") which replaced

 should_start = status & VIRTIO_CONFIG_S_DRIVER_OK;

with

 should_start = virtio_device_started(vdev, status);

which later got replaced by virtio_device_should_start(). This blocked
the possibility to set should_start to false in case the status flag
VIRTIO_CONFIG_S_DRIVER_OK was not set.

Fix it by adjusting the virtio_device_should_start() function to
only consider the status flag instead of vdev->started. Since this
function is only used in the various vhost_*_set_status() functions
for exactly the same purpose, it should be fine to fix it in this
central place there without any risk to change the behavior of other
code.

Fixes: 9f6bcfd99f ("hw/virtio: move vm_running check to virtio_device_started")
Buglink: https://issues.redhat.com/browse/RHEL-40708
Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 include/hw/virtio/virtio.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 7d5ffdc145..2eafad17b8 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -470,9 +470,9 @@ static inline bool virtio_device_started(VirtIODevice *vdev, uint8_t status)
  * @vdev - the VirtIO device
  * @status - the devices status bits
  *
- * This is similar to virtio_device_started() but also encapsulates a
- * check on the VM status which would prevent a device starting
- * anyway.
+ * This is similar to virtio_device_started() but ignores vdev->started
+ * and also encapsulates a check on the VM status which would prevent a
+ * device from starting anyway.
  */
 static inline bool virtio_device_should_start(VirtIODevice *vdev, uint8_t status)
 {
@@ -480,7 +480,7 @@ static inline bool virtio_device_should_start(VirtIODevice *vdev, uint8_t status
         return false;
     }
 
-    return virtio_device_started(vdev, status);
+    return status & VIRTIO_CONFIG_S_DRIVER_OK;
 }
 
 static inline void virtio_set_started(VirtIODevice *vdev, bool started)
-- 
2.45.2

Re: [PATCH] hw/virtio: Fix the de-initialization of vhost-user devices

[Manos Pitsidianakis]

On Tue, 18 Jun 2024 15:19, Thomas Huth <thuth@redhat.com> wrote:
>The unrealize functions of the various vhost-user devices are
>calling the corresponding vhost_*_set_status() functions with a
>status of 0 to shut down the device correctly.
>
>Now these vhost_*_set_status() functions all follow this scheme:
>
>    bool should_start = virtio_device_should_start(vdev, status);
>
>    if (vhost_dev_is_started(&vvc->vhost_dev) == should_start) {
>        return;
>    }
>
>    if (should_start) {
>        /* ... do the initialization stuff ... */
>    } else {
>        /* ... do the cleanup stuff ... */
>    }
>
>The problem here is virtio_device_should_start(vdev, 0) currently
>always returns "true" since it internally only looks at vdev->started
>instead of looking at the "status" parameter. Thus once the device
>got started once, virtio_device_should_start() always returns true


virtio_device_should_start() returning true if it's already started and 
running looks like a code smell to me... it intuitively feels like a 
ternary state instead of boolean: not startable, startable, already 
started.

>and thus the vhost_*_set_status() functions return early, without
>ever doing any clean-up when being called with status == 0. This
>causes e.g. problems when trying to hot-plug and hot-unplug a vhost
>user devices multiple times since the de-initialization step is
>completely skipped during the unplug operation.
>
>This bug has been introduced in commit 9f6bcfd99f ("hw/virtio: move
>vm_running check to virtio_device_started") which replaced
>
> should_start = status & VIRTIO_CONFIG_S_DRIVER_OK;
>
>with
>
> should_start = virtio_device_started(vdev, status);
>
>which later got replaced by virtio_device_should_start(). This blocked
>the possibility to set should_start to false in case the status flag
>VIRTIO_CONFIG_S_DRIVER_OK was not set.
>
>Fix it by adjusting the virtio_device_should_start() function to
>only consider the status flag instead of vdev->started. Since this
>function is only used in the various vhost_*_set_status() functions
>for exactly the same purpose, it should be fine to fix it in this
>central place there without any risk to change the behavior of other
>code.
>
>Fixes: 9f6bcfd99f ("hw/virtio: move vm_running check to virtio_device_started")
>Buglink: https://issues.redhat.com/browse/RHEL-40708
>Signed-off-by: Thomas Huth <thuth@redhat.com>
>---


Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>

Re: [PATCH] hw/virtio: Fix the de-initialization of vhost-user devices

[Thomas Huth]

On 18/06/2024 14.19, Thomas Huth wrote:
> The unrealize functions of the various vhost-user devices are
> calling the corresponding vhost_*_set_status() functions with a
> status of 0 to shut down the device correctly.
> 
> Now these vhost_*_set_status() functions all follow this scheme:
> 
>      bool should_start = virtio_device_should_start(vdev, status);
> 
>      if (vhost_dev_is_started(&vvc->vhost_dev) == should_start) {
>          return;
>      }
> 
>      if (should_start) {
>          /* ... do the initialization stuff ... */
>      } else {
>          /* ... do the cleanup stuff ... */
>      }
> 
> The problem here is virtio_device_should_start(vdev, 0) currently
> always returns "true" since it internally only looks at vdev->started
> instead of looking at the "status" parameter. Thus once the device
> got started once, virtio_device_should_start() always returns true
> and thus the vhost_*_set_status() functions return early, without
> ever doing any clean-up when being called with status == 0. This
> causes e.g. problems when trying to hot-plug and hot-unplug a vhost
> user devices multiple times since the de-initialization step is
> completely skipped during the unplug operation.
> 
> This bug has been introduced in commit 9f6bcfd99f ("hw/virtio: move
> vm_running check to virtio_device_started") which replaced
> 
>   should_start = status & VIRTIO_CONFIG_S_DRIVER_OK;
> 
> with
> 
>   should_start = virtio_device_started(vdev, status);
> 
> which later got replaced by virtio_device_should_start(). This blocked
> the possibility to set should_start to false in case the status flag
> VIRTIO_CONFIG_S_DRIVER_OK was not set.
> 
> Fix it by adjusting the virtio_device_should_start() function to
> only consider the status flag instead of vdev->started. Since this
> function is only used in the various vhost_*_set_status() functions
> for exactly the same purpose, it should be fine to fix it in this
> central place there without any risk to change the behavior of other
> code.
> 
> Fixes: 9f6bcfd99f ("hw/virtio: move vm_running check to virtio_device_started")
> Buglink: https://issues.redhat.com/browse/RHEL-40708
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>   include/hw/virtio/virtio.h | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index 7d5ffdc145..2eafad17b8 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -470,9 +470,9 @@ static inline bool virtio_device_started(VirtIODevice *vdev, uint8_t status)
>    * @vdev - the VirtIO device
>    * @status - the devices status bits
>    *
> - * This is similar to virtio_device_started() but also encapsulates a
> - * check on the VM status which would prevent a device starting
> - * anyway.
> + * This is similar to virtio_device_started() but ignores vdev->started
> + * and also encapsulates a check on the VM status which would prevent a
> + * device from starting anyway.
>    */
>   static inline bool virtio_device_should_start(VirtIODevice *vdev, uint8_t status)
>   {
> @@ -480,7 +480,7 @@ static inline bool virtio_device_should_start(VirtIODevice *vdev, uint8_t status
>           return false;
>       }
>   
> -    return virtio_device_started(vdev, status);
> +    return status & VIRTIO_CONFIG_S_DRIVER_OK;
>   }

Michael, any concerns or comments about this patch?

If not, I could also take it via my s390x tree since this fixes vhost-ccw 
devices on s390x.

  Thomas

Re: [PATCH] hw/virtio: Fix the de-initialization of vhost-user devices

[Michael S. Tsirkin]

On Mon, Jul 01, 2024 at 04:07:56PM +0200, Thomas Huth wrote:
> On 18/06/2024 14.19, Thomas Huth wrote:
> > The unrealize functions of the various vhost-user devices are
> > calling the corresponding vhost_*_set_status() functions with a
> > status of 0 to shut down the device correctly.
> > 
> > Now these vhost_*_set_status() functions all follow this scheme:
> > 
> >      bool should_start = virtio_device_should_start(vdev, status);
> > 
> >      if (vhost_dev_is_started(&vvc->vhost_dev) == should_start) {
> >          return;
> >      }
> > 
> >      if (should_start) {
> >          /* ... do the initialization stuff ... */
> >      } else {
> >          /* ... do the cleanup stuff ... */
> >      }
> > 
> > The problem here is virtio_device_should_start(vdev, 0) currently
> > always returns "true" since it internally only looks at vdev->started
> > instead of looking at the "status" parameter. Thus once the device
> > got started once, virtio_device_should_start() always returns true
> > and thus the vhost_*_set_status() functions return early, without
> > ever doing any clean-up when being called with status == 0. This
> > causes e.g. problems when trying to hot-plug and hot-unplug a vhost
> > user devices multiple times since the de-initialization step is
> > completely skipped during the unplug operation.
> > 
> > This bug has been introduced in commit 9f6bcfd99f ("hw/virtio: move
> > vm_running check to virtio_device_started") which replaced
> > 
> >   should_start = status & VIRTIO_CONFIG_S_DRIVER_OK;
> > 
> > with
> > 
> >   should_start = virtio_device_started(vdev, status);
> > 
> > which later got replaced by virtio_device_should_start(). This blocked
> > the possibility to set should_start to false in case the status flag
> > VIRTIO_CONFIG_S_DRIVER_OK was not set.
> > 
> > Fix it by adjusting the virtio_device_should_start() function to
> > only consider the status flag instead of vdev->started. Since this
> > function is only used in the various vhost_*_set_status() functions
> > for exactly the same purpose, it should be fine to fix it in this
> > central place there without any risk to change the behavior of other
> > code.
> > 
> > Fixes: 9f6bcfd99f ("hw/virtio: move vm_running check to virtio_device_started")
> > Buglink: https://issues.redhat.com/browse/RHEL-40708
> > Signed-off-by: Thomas Huth <thuth@redhat.com>
> > ---
> >   include/hw/virtio/virtio.h | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> > index 7d5ffdc145..2eafad17b8 100644
> > --- a/include/hw/virtio/virtio.h
> > +++ b/include/hw/virtio/virtio.h
> > @@ -470,9 +470,9 @@ static inline bool virtio_device_started(VirtIODevice *vdev, uint8_t status)
> >    * @vdev - the VirtIO device
> >    * @status - the devices status bits
> >    *
> > - * This is similar to virtio_device_started() but also encapsulates a
> > - * check on the VM status which would prevent a device starting
> > - * anyway.
> > + * This is similar to virtio_device_started() but ignores vdev->started
> > + * and also encapsulates a check on the VM status which would prevent a
> > + * device from starting anyway.
> >    */
> >   static inline bool virtio_device_should_start(VirtIODevice *vdev, uint8_t status)
> >   {
> > @@ -480,7 +480,7 @@ static inline bool virtio_device_should_start(VirtIODevice *vdev, uint8_t status
> >           return false;
> >       }
> > -    return virtio_device_started(vdev, status);
> > +    return status & VIRTIO_CONFIG_S_DRIVER_OK;
> >   }
> 
> Michael, any concerns or comments about this patch?
> 
> If not, I could also take it via my s390x tree since this fixes vhost-ccw
> devices on s390x.
> 
>  Thomas

I'm working on a pull request with this today.
I can drop it if you prefer ...

Re: [PATCH] hw/virtio: Fix the de-initialization of vhost-user devices

[Thomas Huth]

On 01/07/2024 17.06, Michael S. Tsirkin wrote:
> On Mon, Jul 01, 2024 at 04:07:56PM +0200, Thomas Huth wrote:
>> On 18/06/2024 14.19, Thomas Huth wrote:
>>> The unrealize functions of the various vhost-user devices are
>>> calling the corresponding vhost_*_set_status() functions with a
>>> status of 0 to shut down the device correctly.
>>>
>>> Now these vhost_*_set_status() functions all follow this scheme:
>>>
>>>       bool should_start = virtio_device_should_start(vdev, status);
>>>
>>>       if (vhost_dev_is_started(&vvc->vhost_dev) == should_start) {
>>>           return;
>>>       }
>>>
>>>       if (should_start) {
>>>           /* ... do the initialization stuff ... */
>>>       } else {
>>>           /* ... do the cleanup stuff ... */
>>>       }
>>>
>>> The problem here is virtio_device_should_start(vdev, 0) currently
>>> always returns "true" since it internally only looks at vdev->started
>>> instead of looking at the "status" parameter. Thus once the device
>>> got started once, virtio_device_should_start() always returns true
>>> and thus the vhost_*_set_status() functions return early, without
>>> ever doing any clean-up when being called with status == 0. This
>>> causes e.g. problems when trying to hot-plug and hot-unplug a vhost
>>> user devices multiple times since the de-initialization step is
>>> completely skipped during the unplug operation.
>>>
>>> This bug has been introduced in commit 9f6bcfd99f ("hw/virtio: move
>>> vm_running check to virtio_device_started") which replaced
>>>
>>>    should_start = status & VIRTIO_CONFIG_S_DRIVER_OK;
>>>
>>> with
>>>
>>>    should_start = virtio_device_started(vdev, status);
>>>
>>> which later got replaced by virtio_device_should_start(). This blocked
>>> the possibility to set should_start to false in case the status flag
>>> VIRTIO_CONFIG_S_DRIVER_OK was not set.
>>>
>>> Fix it by adjusting the virtio_device_should_start() function to
>>> only consider the status flag instead of vdev->started. Since this
>>> function is only used in the various vhost_*_set_status() functions
>>> for exactly the same purpose, it should be fine to fix it in this
>>> central place there without any risk to change the behavior of other
>>> code.
>>>
>>> Fixes: 9f6bcfd99f ("hw/virtio: move vm_running check to virtio_device_started")
>>> Buglink: https://issues.redhat.com/browse/RHEL-40708
>>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>>> ---
>>>    include/hw/virtio/virtio.h | 8 ++++----
>>>    1 file changed, 4 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
>>> index 7d5ffdc145..2eafad17b8 100644
>>> --- a/include/hw/virtio/virtio.h
>>> +++ b/include/hw/virtio/virtio.h
>>> @@ -470,9 +470,9 @@ static inline bool virtio_device_started(VirtIODevice *vdev, uint8_t status)
>>>     * @vdev - the VirtIO device
>>>     * @status - the devices status bits
>>>     *
>>> - * This is similar to virtio_device_started() but also encapsulates a
>>> - * check on the VM status which would prevent a device starting
>>> - * anyway.
>>> + * This is similar to virtio_device_started() but ignores vdev->started
>>> + * and also encapsulates a check on the VM status which would prevent a
>>> + * device from starting anyway.
>>>     */
>>>    static inline bool virtio_device_should_start(VirtIODevice *vdev, uint8_t status)
>>>    {
>>> @@ -480,7 +480,7 @@ static inline bool virtio_device_should_start(VirtIODevice *vdev, uint8_t status
>>>            return false;
>>>        }
>>> -    return virtio_device_started(vdev, status);
>>> +    return status & VIRTIO_CONFIG_S_DRIVER_OK;
>>>    }
>>
>> Michael, any concerns or comments about this patch?
>>
>> If not, I could also take it via my s390x tree since this fixes vhost-ccw
>> devices on s390x.
>>
>>   Thomas
> 
> I'm working on a pull request with this today.
> I can drop it if you prefer ...

Ah, perfect, please include it in your PR then!

  Thanks,
   Thomas