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)
--
2.45.2On 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
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 ...
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
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>
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