Xen project Mailing List

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

On Wed, Aug 06, 2014 at 09:47:43PM +0200, Sander Eikelenboom wrote: > > Wednesday, August 6, 2014, 9:39:16 PM, you wrote: > > > On Wed, Aug 06, 2014 at 09:25:59PM +0200, Sander Eikelenboom wrote: > >> > >> Wednesday, August 6, 2014, 9:18:31 PM, you wrote: > >> > >> > 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: > >> > >> Preliminary in the sense: "this should fix it .. needs more testing" ? > > > This should fix it, albeit the fix has a disastrous flaw. Here is the > > proper version: > > > > From 00a5b6e3c9ee2c2d605879bdaebc627fa640b024 Mon Sep 17 00:00:00 2001 > > From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> > > 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. > > > Reported-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx> > > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> > > --- > > drivers/xen/xen-pciback/pci_stub.c | 25 +++++++++++++++++++++---- > > 1 files changed, 21 insertions(+), 4 deletions(-) > > > diff --git a/drivers/xen/xen-pciback/pci_stub.c > > b/drivers/xen/xen-pciback/pci_stub.c > > index 1ddd22f..8cf7f2b 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); > > > > @@ -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)) > > + dev_info(&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 binded to us). > > + */ > > + 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); > > + } > > /* This disables the device. */ > > xen_pcibk_reset_device(dev); > > > > > Is it save to have "__pci_reset_function_locked(dev)" to be conditional on > succes of > "pci_load_and_free_saved_state" ? It could be redone a bit differently - as in: rc = pci_load_and_free_saved_state(..); __pci_reset_function_locked(dev); if (!rc) { pci_restore_state(dev); ... In which case we will only do the restore state (and save state) when the device is in expected state. And the reset happens at that point. > > Or is it safer because you don't reset the device although it's in an unknown > state (and resetting it while it's back to dom0 could lead to more problems > ?) It could very well lead to disaster. I am not exactly sure what the ramifications are with a device for which we cannot save PCI configuration space - aka - extremely borked. > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel

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