[PATCH v2] vfio_pci: Replace pci_try_reset_function() with __pci_reset_function_locked() to ensure that the pci device configuration space is restored to its original state

[PATCH v2] vfio_pci: Replace pci_try_reset_function() with __pci_reset_function_locked() to ensure that the pci device configuration space is restored to its original state

[hexin]

In vfio_pci_enable(), save the device's initial configuration information
and then restore the configuration in vfio_pci_disable(). However, the
execution result is not the same. Since the pci_try_reset_function()
function saves the current state before resetting, the configuration
information restored by pci_load_and_free_saved_state() will be
overwritten. The __pci_reset_function_locked() function can be used
to prevent the configuration space from being overwritten.

Fixes: 890ed578df82 ("vfio-pci: Use pci "try" reset interface")
Signed-off-by: hexin <hexin15@baidu.com>
Signed-off-by: Liu Qi <liuqi16@baidu.com>
Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
---
 drivers/vfio/pci/vfio_pci.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 703948c..0220616 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -438,11 +438,20 @@ static void vfio_pci_disable(struct vfio_pci_device *vdev)
 	pci_write_config_word(pdev, PCI_COMMAND, PCI_COMMAND_INTX_DISABLE);
 
 	/*
-	 * Try to reset the device.  The success of this is dependent on
-	 * being able to lock the device, which is not always possible.
+	 * Try to get the locks ourselves to prevent a deadlock. The
+	 * success of this is dependent on being able to lock the device,
+	 * which is not always possible.
+	 * We can not use the "try" reset interface here, which will
+	 * overwrite the previously restored configuration information.
 	 */
-	if (vdev->reset_works && !pci_try_reset_function(pdev))
-		vdev->needs_reset = false;
+	if (vdev->reset_works && pci_cfg_access_trylock(pdev)) {
+		if (device_trylock(&pdev->dev)) {
+			if (!__pci_reset_function_locked(pdev))
+				vdev->needs_reset = false;
+			device_unlock(&pdev->dev);
+		}
+		pci_cfg_access_unlock(pdev);
+	}
 
 	pci_restore_state(pdev);
 out:
-- 
1.8.3.1

Re: [PATCH v2] vfio_pci: Replace pci_try_reset_function() with __pci_reset_function_locked() to ensure that the pci device configuration space is restored to its original state

[Alex Williamson]

On Sat, 17 Aug 2019 19:51:03 +0800
hexin <hexin.op@gmail.com> wrote:

> In vfio_pci_enable(), save the device's initial configuration information
> and then restore the configuration in vfio_pci_disable(). However, the
> execution result is not the same. Since the pci_try_reset_function()
> function saves the current state before resetting, the configuration
> information restored by pci_load_and_free_saved_state() will be
> overwritten. The __pci_reset_function_locked() function can be used
> to prevent the configuration space from being overwritten.
> 
> Fixes: 890ed578df82 ("vfio-pci: Use pci "try" reset interface")
> Signed-off-by: hexin <hexin15@baidu.com>
> Signed-off-by: Liu Qi <liuqi16@baidu.com>
> Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
> ---
>  drivers/vfio/pci/vfio_pci.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)

This looks good, but the subject is too long and I find the commit log
somewhat confusing.  May I update these as follows?

    vfio_pci: Restore original state on release
    
    vfio_pci_enable() saves the device's initial configuration information
    with the intent that it is restored in vfio_pci_disable().  However,
    commit 890ed578df82 ("vfio-pci: Use pci "try" reset interface")
    replaced the call to __pci_reset_function_locked(), which is not wrapped
    in a state save and restore, with pci_try_reset_function(), which
    overwrites the restored device state with the current state before
    applying it to the device.  Restore use of __pci_reset_function_locked()
    to return to the desired behavior.

Thanks,
Alex


> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index 703948c..0220616 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -438,11 +438,20 @@ static void vfio_pci_disable(struct vfio_pci_device *vdev)
>  	pci_write_config_word(pdev, PCI_COMMAND, PCI_COMMAND_INTX_DISABLE);
>  
>  	/*
> -	 * Try to reset the device.  The success of this is dependent on
> -	 * being able to lock the device, which is not always possible.
> +	 * Try to get the locks ourselves to prevent a deadlock. The
> +	 * success of this is dependent on being able to lock the device,
> +	 * which is not always possible.
> +	 * We can not use the "try" reset interface here, which will
> +	 * overwrite the previously restored configuration information.
>  	 */
> -	if (vdev->reset_works && !pci_try_reset_function(pdev))
> -		vdev->needs_reset = false;
> +	if (vdev->reset_works && pci_cfg_access_trylock(pdev)) {
> +		if (device_trylock(&pdev->dev)) {
> +			if (!__pci_reset_function_locked(pdev))
> +				vdev->needs_reset = false;
> +			device_unlock(&pdev->dev);
> +		}
> +		pci_cfg_access_unlock(pdev);
> +	}
>  
>  	pci_restore_state(pdev);
>  out:

Re: [PATCH v2] vfio_pci: Replace pci_try_reset_function() with __pci_reset_function_locked() to ensure that the pci device configuration space is restored to its original state

[hexin]

Alex Williamson <alex.williamson@redhat.com> 于2019年8月20日周二 上午3:53写道：
>
> On Sat, 17 Aug 2019 19:51:03 +0800
> hexin <hexin.op@gmail.com> wrote:
>
> > In vfio_pci_enable(), save the device's initial configuration information
> > and then restore the configuration in vfio_pci_disable(). However, the
> > execution result is not the same. Since the pci_try_reset_function()
> > function saves the current state before resetting, the configuration
> > information restored by pci_load_and_free_saved_state() will be
> > overwritten. The __pci_reset_function_locked() function can be used
> > to prevent the configuration space from being overwritten.
> >
> > Fixes: 890ed578df82 ("vfio-pci: Use pci "try" reset interface")
> > Signed-off-by: hexin <hexin15@baidu.com>
> > Signed-off-by: Liu Qi <liuqi16@baidu.com>
> > Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
> > ---
> >  drivers/vfio/pci/vfio_pci.c | 17 +++++++++++++----
> >  1 file changed, 13 insertions(+), 4 deletions(-)
>
> This looks good, but the subject is too long and I find the commit log
> somewhat confusing.  May I update these as follows?
>
>     vfio_pci: Restore original state on release
>
>     vfio_pci_enable() saves the device's initial configuration information
>     with the intent that it is restored in vfio_pci_disable().  However,
>     commit 890ed578df82 ("vfio-pci: Use pci "try" reset interface")
>     replaced the call to __pci_reset_function_locked(), which is not wrapped
>     in a state save and restore, with pci_try_reset_function(), which
>     overwrites the restored device state with the current state before
>     applying it to the device.  Restore use of __pci_reset_function_locked()
>     to return to the desired behavior.
>
> Thanks,
> Alex
>
>

Thanks for your update, the updated commit log is clearer than before.
At the same time, when I use checkpatch.pl to detect the patch, there
will be the
following error:

ERROR: Please use git commit description style 'commit <12+ chars of
sha1> ("<title line>")'
- ie: 'commit 890ed578df82 ("vfio-pci: Use pci "try" reset interface")'

Line 2785 ~ 2801 in checkpatch.pl, the script can't handle the commit message
which contains double quotes because of the expression `([^"]+)`. Like
the "try" above.
Maybe checkpatch.pl needs to be modified.

Thanks，
HeXin


> > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> > index 703948c..0220616 100644
> > --- a/drivers/vfio/pci/vfio_pci.c
> > +++ b/drivers/vfio/pci/vfio_pci.c
> > @@ -438,11 +438,20 @@ static void vfio_pci_disable(struct vfio_pci_device *vdev)
> >       pci_write_config_word(pdev, PCI_COMMAND, PCI_COMMAND_INTX_DISABLE);
> >
> >       /*
> > -      * Try to reset the device.  The success of this is dependent on
> > -      * being able to lock the device, which is not always possible.
> > +      * Try to get the locks ourselves to prevent a deadlock. The
> > +      * success of this is dependent on being able to lock the device,
> > +      * which is not always possible.
> > +      * We can not use the "try" reset interface here, which will
> > +      * overwrite the previously restored configuration information.
> >        */
> > -     if (vdev->reset_works && !pci_try_reset_function(pdev))
> > -             vdev->needs_reset = false;
> > +     if (vdev->reset_works && pci_cfg_access_trylock(pdev)) {
> > +             if (device_trylock(&pdev->dev)) {
> > +                     if (!__pci_reset_function_locked(pdev))
> > +                             vdev->needs_reset = false;
> > +                     device_unlock(&pdev->dev);
> > +             }
> > +             pci_cfg_access_unlock(pdev);
> > +     }
> >
> >       pci_restore_state(pdev);
> >  out:
>

Re: [PATCH v2] vfio_pci: Replace pci_try_reset_function() with __pci_reset_function_locked() to ensure that the pci device configuration space is restored to its original state

[Alex Williamson]

On Wed, 21 Aug 2019 23:13:08 +0800
hexin <hexin.op@gmail.com> wrote:

> Alex Williamson <alex.williamson@redhat.com> 于2019年8月20日周二 上午3:53写道：
> >
> > On Sat, 17 Aug 2019 19:51:03 +0800
> > hexin <hexin.op@gmail.com> wrote:
> >  
> > > In vfio_pci_enable(), save the device's initial configuration information
> > > and then restore the configuration in vfio_pci_disable(). However, the
> > > execution result is not the same. Since the pci_try_reset_function()
> > > function saves the current state before resetting, the configuration
> > > information restored by pci_load_and_free_saved_state() will be
> > > overwritten. The __pci_reset_function_locked() function can be used
> > > to prevent the configuration space from being overwritten.
> > >
> > > Fixes: 890ed578df82 ("vfio-pci: Use pci "try" reset interface")
> > > Signed-off-by: hexin <hexin15@baidu.com>
> > > Signed-off-by: Liu Qi <liuqi16@baidu.com>
> > > Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
> > > ---
> > >  drivers/vfio/pci/vfio_pci.c | 17 +++++++++++++----
> > >  1 file changed, 13 insertions(+), 4 deletions(-)  
> >
> > This looks good, but the subject is too long and I find the commit log
> > somewhat confusing.  May I update these as follows?
> >
> >     vfio_pci: Restore original state on release
> >
> >     vfio_pci_enable() saves the device's initial configuration information
> >     with the intent that it is restored in vfio_pci_disable().  However,
> >     commit 890ed578df82 ("vfio-pci: Use pci "try" reset interface")
> >     replaced the call to __pci_reset_function_locked(), which is not wrapped
> >     in a state save and restore, with pci_try_reset_function(), which
> >     overwrites the restored device state with the current state before
> >     applying it to the device.  Restore use of __pci_reset_function_locked()
> >     to return to the desired behavior.
> >
> > Thanks,
> > Alex
> >
> >  
> 
> Thanks for your update, the updated commit log is clearer than before.
> At the same time, when I use checkpatch.pl to detect the patch, there
> will be the
> following error:
> 
> ERROR: Please use git commit description style 'commit <12+ chars of
> sha1> ("<title line>")'  
> - ie: 'commit 890ed578df82 ("vfio-pci: Use pci "try" reset interface")'
> 
> Line 2785 ~ 2801 in checkpatch.pl, the script can't handle the commit message
> which contains double quotes because of the expression `([^"]+)`. Like
> the "try" above.
> Maybe checkpatch.pl needs to be modified.

I think we're following the intention of the rule, and as you've
identified it's the implementation of the rule checker that's unable
to handle a commit title with internal quotes.  We can ignore it, and
maybe follow up with a checkpatch.pl patch, or we could just avoid it
as follows:

    vfio_pci: Restore original state on release
    
    vfio_pci_enable() saves the device's initial configuration information
    with the intent that it is restored in vfio_pci_disable().  However,
    the commit referenced in Fixes: below replaced the call to
    __pci_reset_function_locked(), which is not wrapped in a state save
    and restore, with pci_try_reset_function(), which overwrites the
    restored device state with the current state before applying it to the
    device.  Reinstate use of __pci_reset_function_locked() to return to
    the desired behavior.

Thanks,
Alex

> > > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> > > index 703948c..0220616 100644
> > > --- a/drivers/vfio/pci/vfio_pci.c
> > > +++ b/drivers/vfio/pci/vfio_pci.c
> > > @@ -438,11 +438,20 @@ static void vfio_pci_disable(struct vfio_pci_device *vdev)
> > >       pci_write_config_word(pdev, PCI_COMMAND, PCI_COMMAND_INTX_DISABLE);
> > >
> > >       /*
> > > -      * Try to reset the device.  The success of this is dependent on
> > > -      * being able to lock the device, which is not always possible.
> > > +      * Try to get the locks ourselves to prevent a deadlock. The
> > > +      * success of this is dependent on being able to lock the device,
> > > +      * which is not always possible.
> > > +      * We can not use the "try" reset interface here, which will
> > > +      * overwrite the previously restored configuration information.
> > >        */
> > > -     if (vdev->reset_works && !pci_try_reset_function(pdev))
> > > -             vdev->needs_reset = false;
> > > +     if (vdev->reset_works && pci_cfg_access_trylock(pdev)) {
> > > +             if (device_trylock(&pdev->dev)) {
> > > +                     if (!__pci_reset_function_locked(pdev))
> > > +                             vdev->needs_reset = false;
> > > +                     device_unlock(&pdev->dev);
> > > +             }
> > > +             pci_cfg_access_unlock(pdev);
> > > +     }
> > >
> > >       pci_restore_state(pdev);
> > >  out:  
> >