On 06/08/14 20:39, Konrad Rzeszutek Wilk wrote:
>
> From 00a5b6e3c9ee2c2d605879bdaebc627fa640b024 Mon Sep 17 00:00:00 2001
> From: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
> Date: Wed, 6 Aug 2014 16:21:32 -0400
> Subject: [PATCH] xen/pciback: Restore configuration space when detaching from
> a guest.
>
> The commit 9eea3f7695226f9af9992cebf8e98ac0ad78b277
> "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.
>
> To still retain the PCI configuration space, we save it once
> more and store it on our private copy to be restored when:
> - Device is unbinded from pciback
> - Device is detached from a guest.
This should be folded into the original patch.
[...]
> --- 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))
I dislike testing for errors like this as it looks like it's testing for
a boolean success. Use
ret = pci_load_and_free_saved_state(...);
if (ret < 0)
...
And similarly, below.
> - dev_dbg(&dev->dev, "Could not reload PCI state\n");
> + dev_info(&dev->dev, "Could not reload PCI state\n");
This should be dev_warn().
pci_load_and_free_saved_state() won't fail because we know the state is
valid (since we saved it from the device originally). Warning and
skipping the restore is fine here (and below).
> else
> pci_restore_state(dev);
>
> @@ -257,6 +257,7 @@ 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;
>
> spin_lock_irqsave(&pcistub_devices_lock, flags);
>
> @@ -279,9 +280,25 @@ 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);
> + if (pci_load_and_free_saved_state(dev, &dev_data->pci_saved_state))
This should be pci_load_saved_state() and then you can avoid the
pci_save_state() below.
> + dev_info(&dev->dev, "Could not reload PCI state\n");
dev_warn() also.
> + 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 binded to us).
s/binded/bound/
> + pci_restore_state(dev);
> + /*
> + * The next steps are to reload the configuration for the
> + * next time we bind & unbind to a guest - or unload from
> + * pciback.
> + */
> + pci_save_state(dev);
> + dev_data->pci_saved_state = pci_store_saved_state(dev);
You don't need this if you don't free the original state above.
> + }
> /* This disables the device. */
> xen_pcibk_reset_device(dev);
David
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