Patch "virtio_pci: fix cpu affinity support" has been added to the 4.12-stable tree

This is a note to let you know that I've just added the patch titled

virtio_pci: fix cpu affinity support

to the 4.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
virtio_pci-fix-cpu-affinity-support.patch
and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Christoph Hellwig <[email protected]>
Date: Thu, 24 Aug 2017 18:07:02 +0200
Subject: virtio_pci: fix cpu affinity support

From: Christoph Hellwig <[email protected]>

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.

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

@@ -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;

Patches currently in stable-queue which might be from [email protected] are

queue-4.12/virtio_pci-fix-cpu-affinity-support.patch queue-4.12/x86-mm-fix-use-after-free-of-ldt_struct.patch queue-4.12/dax-fix-deadlock-due-to-misaligned-pmd-faults.patch