On Fri, 16 Aug 2019 11:33:47 +0800
hexin <hexin.op@xxxxxxxxx> 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.
>
> Signed-off-by: hexin <hexin15@xxxxxxxxx>
> Signed-off-by: Liu Qi <liuqi16@xxxxxxxxx>
> Signed-off-by: Zhang Yu <zhangyu31@xxxxxxxxx>
> ---
> drivers/vfio/pci/vfio_pci.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index 703948c..3c93492 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -441,8 +441,14 @@ static void vfio_pci_disable(struct vfio_pci_device *vdev)
> * Try to reset the device. The success of this is dependent on
> * being able to lock the device, which is not always possible.
> */
> - 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:
This used to work, I think what happened is that we initially called
__pci_reset_function() to avoid the saved state getting overwritten,
then commit d24cdbfd28b7 ("vfio-pci: Avoid deadlock on remove") added
the trylock support to avoid deadlock, then commit 890ed578df82
("vfio-pci: Use pci "try" reset interface") assumed the trylock was the
reason for the unusual calling convention and simply replaced it with
pci_try_reset_function(). So, I think we need two things. First, a
fixes tag:
Fixes: 890ed578df82 ("vfio-pci: Use pci "try" reset interface")
Second, a comment to warn us against performing a similar cleanup again
in the future. Thanks,
Alex
