[PATCH 4.12 72/99] virtio_pci: fix cpu affinity support

[Greg Kroah-Hartman]

4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christoph Hellwig <hch@xxxxxx>

commit ba74b6f7fcc07355d087af6939712eed4a454821 upstream.

Commit 0b0f9dc5 ("Revert "virtio_pci: use shared interrupts for
virtqueues"") removed the adjustment of the pre_vectors for the virtio
MSI-X vector allocation which was added in commit fb5e31d9 ("virtio:
allow drivers to request IRQ affinity when creating VQs"). This will
lead to an incorrect assignment of MSI-X vectors, and potential
deadlocks when offlining cpus.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Fixes: 0b0f9dc5 ("Revert "virtio_pci: use shared interrupts for virtqueues")
Reported-by: YASUAKI ISHIMATSU <yasu.isimatu@xxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/virtio/virtio_pci_common.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/drivers/virtio/virtio_pci_common.c
+++ b/drivers/virtio/virtio_pci_common.c
@@ -107,6 +107,7 @@ static int vp_request_msix_vectors(struc
 {
 	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
 	const char *name = dev_name(&vp_dev->vdev.dev);
+	unsigned flags = PCI_IRQ_MSIX;
 	unsigned i, v;
 	int err = -ENOMEM;
 
@@ -126,10 +127,13 @@ static int vp_request_msix_vectors(struc
 					GFP_KERNEL))
 			goto error;
 
+	if (desc) {
+		flags |= PCI_IRQ_AFFINITY;
+		desc->pre_vectors++; /* virtio config vector */
+	}
+
 	err = pci_alloc_irq_vectors_affinity(vp_dev->pci_dev, nvectors,
-					     nvectors, PCI_IRQ_MSIX |
-					     (desc ? PCI_IRQ_AFFINITY : 0),
-					     desc);
+					     nvectors, flags, desc);
 	if (err < 0)
 		goto error;
 	vp_dev->msix_enabled = 1;