Patch "vfio/pci: Virtualize Maximum Payload Size" has been added to the 4.9-stable tree

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

vfio/pci: Virtualize Maximum Payload Size

to the 4.9-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:
vfio-pci-virtualize-maximum-payload-size.patch
and it can be found in the queue-4.9 subdirectory.

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

From: Alex Williamson <[email protected]>
Date: Mon, 2 Oct 2017 12:39:09 -0600
Subject: vfio/pci: Virtualize Maximum Payload Size

From: Alex Williamson <[email protected]>

[ Upstream commit 523184972b282cd9ca17a76f6ca4742394856818 ]

With virtual PCI-Express chipsets, we now see userspace/guest drivers trying to match the physical MPS setting to a virtual downstream port. Of course a lone physical device surrounded by virtual interconnects cannot make a correct decision for a proper MPS setting. Instead, let's virtualize the MPS control register so that writes through to hardware are disallowed. Userspace drivers like QEMU assume they can write anything to the device and we'll filter out anything dangerous. Since mismatched MPS can lead to AER and other faults, let's add it to the kernel side rather than relying on userspace virtualization to handle it.

---
 drivers/vfio/pci/vfio_pci_config.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

@@ -851,11 +851,13 @@ static int __init init_pci_cap_exp_perm(
 
 	/*
 	 * Allow writes to device control fields, except devctl_phantom,
-	 * which could confuse IOMMU, and the ARI bit in devctl2, which
+	 * which could confuse IOMMU, MPS, which can break communication
+	 * with other physical devices, and the ARI bit in devctl2, which
 	 * is set at probe time.  FLR gets virtualized via our writefn.
 	 */
 	p_setw(perm, PCI_EXP_DEVCTL,
-	       PCI_EXP_DEVCTL_BCR_FLR, ~PCI_EXP_DEVCTL_PHANTOM);
+	       PCI_EXP_DEVCTL_BCR_FLR | PCI_EXP_DEVCTL_PAYLOAD,
+	       ~PCI_EXP_DEVCTL_PHANTOM);
 	p_setw(perm, PCI_EXP_DEVCTL2, NO_VIRT, ~PCI_EXP_DEVCTL2_ARI);
 	return 0;
 }

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

queue-4.9/pci-avoid-bus-reset-if-bridge-itself-is-broken.patch queue-4.9/vfio-pci-virtualize-maximum-payload-size.patch