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SubjectRe: [Xen-devel] [PATCH v4 7/7] xen/pciback: Restore configuration space when detaching from a guest.
On 11/21/2014 05:17 PM, Konrad Rzeszutek Wilk wrote:
> The commit "xen/pciback: Don't deadlock when unbinding." was using
> the version of pci_reset_function which would lock the device lock.
> That is no good as we can dead-lock. As such we swapped to using
> the lock-less version and requiring that the callers
> of 'pcistub_put_pci_dev' take the device lock. And as such
> this bug got exposed.
>
> Using the lock-less version is OK, except that we tried to
> use 'pci_restore_state' after the lock-less version of
> __pci_reset_function_locked - which won't work as 'state_saved'
> is set to false. Said 'state_saved' is a toggle boolean that
> is to be used by the sequence of a) pci_save_state/pci_restore_state
> or b) pci_load_and_free_saved_state/pci_restore_state. We don't
> want to use a) as the guest might have messed up the PCI
> configuration space and we want it to revert to the state
> when the PCI device was binded to us. Therefore we pick
> b) to restore the configuration space.


Doesn't this all mean that patch 1/7 broke pcistub_put_pci_dev()?

-boris


>
> We restore from our 'golden' version of PCI configuration space, when an:
> - Device is unbinded from pciback
> - Device is detached from a guest.
>
> Reported-by: Sander Eikelenboom <linux@eikelenboom.it>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> ---
> drivers/xen/xen-pciback/pci_stub.c | 20 ++++++++++++++++----
> 1 file changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c
> index 843a2ba..eb8b58e 100644
> --- a/drivers/xen/xen-pciback/pci_stub.c
> +++ b/drivers/xen/xen-pciback/pci_stub.c
> @@ -105,7 +105,7 @@ static void pcistub_device_release(struct kref *kref)
> */
> __pci_reset_function_locked(dev);
> if (pci_load_and_free_saved_state(dev, &dev_data->pci_saved_state))
> - dev_dbg(&dev->dev, "Could not reload PCI state\n");
> + dev_info(&dev->dev, "Could not reload PCI state\n");
> else
> pci_restore_state(dev);
>
> @@ -257,6 +257,8 @@ void pcistub_put_pci_dev(struct pci_dev *dev)
> {
> struct pcistub_device *psdev, *found_psdev = NULL;
> unsigned long flags;
> + struct xen_pcibk_dev_data *dev_data;
> + int ret;
>
> spin_lock_irqsave(&pcistub_devices_lock, flags);
>
> @@ -279,9 +281,19 @@ void pcistub_put_pci_dev(struct pci_dev *dev)
> * (so it's ready for the next domain)
> */
> device_lock_assert(&dev->dev);
> - __pci_reset_function_locked(dev);
> - pci_restore_state(dev);
> -
> + dev_data = pci_get_drvdata(dev);
> + ret = pci_load_saved_state(dev, dev_data->pci_saved_state);
> + if (ret < 0)
> + dev_warn(&dev->dev, "Could not reload PCI state\n");
> + else {
> + __pci_reset_function_locked(dev);
> + /*
> + * The usual sequence is pci_save_state & pci_restore_state
> + * but the guest might have messed the configuration space up.
> + * Use the initial version (when device was bound to us).
> + */
> + pci_restore_state(dev);
> + }
> /* This disables the device. */
> xen_pcibk_reset_device(dev);
>



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