linux-kernel - 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

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Message-ID: <CAB_WELYZ80FHyjkcXj4WvBVx-N-3ZMURN3OXTqqbELVn90157g@mail.gmail.com>
Date:   Wed, 21 Aug 2019 23:13:08 +0800
From:   hexin <hexin.op@...il.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     kvm@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, hexin <hexin15@...du.com>,
        Liu Qi <liuqi16@...du.com>, Zhang Yu <zhangyu31@...du.com>
Subject: 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 <alex.williamson@...hat.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@...il.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@...du.com>
> > Signed-off-by: Liu Qi <liuqi16@...du.com>
> > Signed-off-by: Zhang Yu <zhangyu31@...du.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:
>