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Subject[PATCH] x86/PCI: Fully disable devices before releasing IRQ resource
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The IRQ resource for a device is established when pci_enabled_device()
is called on a fully disabled device (ie. enable_cnt == 0). With
commit b4b55cda5874 ("x86/PCI: Refine the way to release PCI IRQ
resources") this same IRQ resource is released when the driver is
unbound from the device, regardless of the enable_cnt. This presents
the situation that an ill-behaved driver can now make a device
unusable to subsequent drivers by an imbalance in their use of
pci_enable/disable_device(). It's one thing to break your own device
if you're one of these ill-behaved drivers, but it's a serious
regression for secondary drivers like vfio-pci, which are innocent
of the transgressions of the previous driver.

Resolve by pushing the device to a fully disabled state before
releasing the IRQ resource.

Fixes: b4b55cda5874 ("x86/PCI: Refine the way to release PCI IRQ resources")
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
---
arch/x86/pci/common.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
index 3d2612b..4810194 100644
--- a/arch/x86/pci/common.c
+++ b/arch/x86/pci/common.c
@@ -527,8 +527,19 @@ static int pci_irq_notifier(struct notifier_block *nb, unsigned long action,
if (action != BUS_NOTIFY_UNBOUND_DRIVER)
return NOTIFY_DONE;

- if (pcibios_disable_irq)
+ if (pcibios_disable_irq) {
+ /*
+ * Broken drivers may allow a device to be .remove()'d while
+ * still enabled. pci_enable_device() will only re-establish
+ * dev->irq if the devices is fully disabled. So if we want
+ * to release the IRQ, we need to make sure the next driver
+ * can re-establish it using pci_enable_device().
+ */
+ while (pci_is_enabled(dev))
+ pci_disable_device(dev);
+
pcibios_disable_irq(dev);
+ }

return NOTIFY_OK;
}


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