Re: [Xen-devel] [PATCH v5] Fixes to Xen pciback for 3.17.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Aug 06, 2014 at 08:59:59PM +0200, Sander Eikelenboom wrote:
> 
> Tuesday, August 5, 2014, 4:04:43 PM, you wrote:
> 
> 
> > Tuesday, August 5, 2014, 3:49:30 PM, you wrote:
> 
> >> On Tue, Aug 05, 2014 at 11:44:33AM +0200, Sander Eikelenboom wrote:
> >>> 
> >>> Tuesday, August 5, 2014, 11:31:08 AM, you wrote:
> >>> 
> >>> > On 05/08/14 09:44, Sander Eikelenboom wrote:
> >>> >> 
> >>> >> Monday, August 4, 2014, 8:43:18 PM, you wrote:
> >>> >> 
> >>> >>> On Fri, Aug 01, 2014 at 04:30:05PM +0100, David Vrabel wrote:
> >>> >>>> On 14/07/14 17:18, Konrad Rzeszutek Wilk wrote:
> >>> >>>>> Greg: goto GHK
> >>> >>>>>
> >>> >>>>> This is v5 version of patches to fix some issues in Xen PCIback.
> >>> >>>>
> >>> >>>> Applied to devel/for-linus-3.17.
> >>> >> 
> >>> >>> Thank you.
> >>> >>>>
> >>> >>>> I dropped the stable Cc for #2 pending a final decision on whether it
> >>> >>>> really is a stable candidate.
> >>> >> 
> >>> >>> OK.
> >>> >>>>
> >>> >>>> David
> >>> >> 
> >>> >> Hi Konrad / David,
> >>> >> 
> >>> >> This series still lacks a resolution on the sysfs /do_flr /reset,
> >>> >> as a result the pci devices are not reset after shutdown of a guest.
> >>> >> (no more pciback 0000:xx:xx.x: restoring config space at offset xxx)
> >>> >> 
> >>> >> So this series now introduces a regression to 3.16, which causes devices to malfunction 
> >>> >> after a guest reboot or after assigning the devices to another guest.
> >>> 
> >>> > I don't follow what you're saying.  The lack of a device reset for PCI
> >>> > devices with no FLR method isn't a regression as this has never worked.
> >>> >  Can you explain in more detail what the regression is and which patch
> >>> > caused it?
> >>> 
> >>> I haven't bisected it to a specific patch in this series,
> >>> but this patch series (when pulled on top of 3.16) cause the following:
> >>> 
> >>> - Do a system start and HVM guest start
> >>> - HVM guest with pci passthrough, devices work fine
> >>> - shutdown the HVM guest
> >>> - "pciback 0000:xx:xx.x: restoring config space at offset xxx" messages do not
> >>>   appear anymore when shutting down the HVM guest (as they do with vanilla 3.16)
> >>> - Starting the HVM guest again with the same devices passed through.
> >>> - Devices malfunction (for example a USB host controller will fail a simple 
> >>>   "lsusb"
> >>> - And this all works fine on vanilla 3.16.  
> 
> >> Hm, the only patch that makes code changes is 63fc5ec97cc54257d1c4ee49ed2131f754a5ff9b
> >> "xen/pciback: Don't deadlock when unbinding."
> >> but it does not change any of that code path. Only figures out whether
> >> to take a lock or not.
> 
> > Ok and the do_flr nack by david is unrelated to this part (i didn't check just 
> > assumed there could be a connection)
> 
> >> I will try it out on my box and see if I can reproduce it.
> 
> >> And just to be 100% sure - you are using vanilla Xen? No changes on top
> >> of it?
> 
> > Except the fix from jan for the pirq/msi stuff (and an unrelated hpet one), other than that no.
> > If you can't reproduce i will see if i can dive deeper into it tonight !
> 
> Hi Konrad,
> 
> It looks like the issues is this part of the change:
> 
>     --- a/drivers/xen/xen-pciback/pci_stub.c
>     +++ b/drivers/xen/xen-pciback/pci_stub.c
>     @@ -250,6 +250,8 @@ struct pci_dev *pcistub_get_pci_dev(struct xen_pcibk_device *pdev,
>     * - 'echo BDF > unbind' with a guest still using it. See pcistub_remove
>     *
>     * As such we have to be careful.
>     + *
>     + * To make this easier, the caller has to hold the device lock.
>     */
>     void pcistub_put_pci_dev(struct pci_dev *dev)
>     {
>     @@ -276,11 +278,8 @@ void pcistub_put_pci_dev(struct pci_dev *dev)
>     /* Cleanup our device
>     * (so it's ready for the next domain)
>     */
>     -
>     - /* This is OK - we are running from workqueue context
>     - * and want to inhibit the user from fiddling with 'reset'
>     - */
>     - pci_reset_function(dev);
>     + lockdep_assert_held(&dev->dev.mutex);
>     + __pci_reset_function_locked(dev);
>     pci_restore_state(dev);
>    /* This disables the device. */
> 
> More specifically:
> The old "pci_reset_function(dev)" potentially seems to do much more than 
> __pci_reset_function_locked(dev).
> 
> 
> "__pci_reset_function_locked(dev)" only calls  "__pci_dev_reset"
> while "pci_reset_function" not only calls pci_dev_reset, but on succes
> it also calls: "pci_dev_save_and_disable" which does a save state etc.
> 
> 
> So i added a little more debug:
> 
> device_lock_assert(&dev->dev);
> ret = __pci_reset_function_locked(dev);
> dev_dbg(&dev->dev, "%s __pci_reset_function_locked:%d  dev->state_saved:%d\n", __func__, ret, (!dev->state_saved) ? 0 : 1 );
> pci_restore_state(dev);
> 
> And this returns:
> [  494.570579] pciback 0000:04:00.0: pcistub_put_pci_dev __pci_reset_function_locked:0  dev->state_saved:0
> 
> So that confirms there is no saved_state to get restored by 
> pci_restore_state(dev) in the next line.
> 
> However there seems to be no "locked" variant of the function 
> "pci_reset_function" in pci.c that has all the same logic ...

Yup. I've a preliminary patch:


diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c
index 1ddd22f..4cb7901 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 +257,7 @@ 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);
 
@@ -278,10 +279,25 @@ void pcistub_put_pci_dev(struct pci_dev *dev)
 	/* Cleanup our device
 	 * (so it's ready for the next domain)
 	 */
-	device_lock_assert(&dev->dev);
-	__pci_reset_function_locked(dev);
-	pci_restore_state(dev);
-
+	if (pci_load_and_free_saved_state(dev, &dev_data->pci_saved_state))
+		dev_info(&dev->dev, "Could not reload PCI state\n");
+	else {
+		device_lock_assert(&dev->dev);
+		__pci_reset_function_locked(dev);
+		/*
+		 * The usual sequence is pci_save_state & pci_restore_state
+		 * but the guest might have messed the config space up. Use
+		 * the initial configuration (when device was binded to us).
+		 */
+		pci_restore_state(dev);
+		/*
+		 * The next steps are to reload the configuration for the
+		 * next time we need to unbind/bind to a guest..
+		 */
+		dev_data = pci_get_drvdata(dev);
+		pci_save_state(dev);
+		dev_data->pci_saved_state = pci_store_saved_state(dev);
+	}
 	/* This disables the device. */
 	xen_pcibk_reset_device(dev);
 
> 
> --
> Sander 
> 
> >> Thanks!
> 
> >>> 
> >>> >> Apart from that .. i can't resist to remind the other issue with removing pci
> >>> >> devices passed through to HVM guests related to the signaling via xenstore,
> >>> >> described in:
> >>> >> 
> >>> >> http://lists.xen.org/archives/html/xen-devel/2014-07/msg01875.html
> >>> 
> >>> > I don't remember seeing you posting a patch...?
> 
> >> I was going to, but I think we need to figure out the 'do_flr' mechanism
> >> first.
> 
> >>> 
> >>> > David
> >>> 
> >>> 
> 
> 
> 
> 
>