pci: Add flag indicating device has been assigned by KVM

Device drivers that create and destroy SR-IOV virtual functions via
calls to pci_enable_sriov() and pci_disable_sriov can cause catastrophic
failures if they attempt to destroy VFs while they are assigned to
guest virtual machines.  By adding a flag for use by the KVM module
to indicate that a device is assigned a device driver can check that
flag and avoid destroying VFs while they are assigned and avoid system
failures.

CC: Ian Campbell <ijc@hellion.org.uk>
CC: Konrad Wilk <konrad.wilk@oracle.com>
Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

include/linux/pci.h

@@ -174,6 +174,8 @@ enum pci_dev_flags {
 	PCI_DEV_FLAGS_MSI_INTX_DISABLE_BUG = (__force pci_dev_flags_t) 1,
 	/* Device configuration is irrevocably lost if disabled into D3 */
 	PCI_DEV_FLAGS_NO_D3 = (__force pci_dev_flags_t) 2,
+	/* Provide indication device is assigned by a Virtual Machine Manager */
+	PCI_DEV_FLAGS_ASSIGNED = (__force pci_dev_flags_t) 4,
 };
 
 enum pci_irq_reroute_variant {

virt/kvm/assigned-dev.c

@@ -205,6 +205,8 @@ static void kvm_free_assigned_device(struct kvm *kvm,
 	else
 		pci_restore_state(assigned_dev->dev);
 
+	assigned_dev->dev->dev_flags &= ~PCI_DEV_FLAGS_ASSIGNED;
+
 	pci_release_regions(assigned_dev->dev);
 	pci_disable_device(assigned_dev->dev);
 	pci_dev_put(assigned_dev->dev);

virt/kvm/iommu.c

@@ -187,6 +187,8 @@ int kvm_assign_device(struct kvm *kvm,
 			goto out_unmap;
 	}
 
+	pdev->dev_flags |= PCI_DEV_FLAGS_ASSIGNED;
+
 	printk(KERN_DEBUG "assign device %x:%x:%x.%x\n",
 		assigned_dev->host_segnr,
 		assigned_dev->host_busnr,
@@ -215,6 +217,8 @@ int kvm_deassign_device(struct kvm *kvm,
 
 	iommu_detach_device(domain, &pdev->dev);
 
+	pdev->dev_flags &= ~PCI_DEV_FLAGS_ASSIGNED;
+
 	printk(KERN_DEBUG "deassign device %x:%x:%x.%x\n",
 		assigned_dev->host_segnr,
 		assigned_dev->host_busnr,