[3.13.y-ckt stable] Patch "xen/pciback: Don't allow MSI-X ops if PCI_COMMAND_MEMORY is not set." has been added to the 3.13.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    xen/pciback: Don't allow MSI-X ops if PCI_COMMAND_MEMORY is not set.

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt33.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 064bdf3395fef119180505ccb3fb9312fa6abe54 Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Date: Mon, 2 Nov 2015 18:13:27 -0500
Subject: xen/pciback: Don't allow MSI-X ops if PCI_COMMAND_MEMORY is not set.

commit 408fb0e5aa7fda0059db282ff58c3b2a4278baa0 upstream.

commit f598282f51 ("PCI: Fix the NIU MSI-X problem in a better way")
teaches us that dealing with MSI-X can be troublesome.

Further checks in the MSI-X architecture shows that if the
PCI_COMMAND_MEMORY bit is turned of in the PCI_COMMAND we
may not be able to access the BAR (since they are memory regions).

Since the MSI-X tables are located in there.. that can lead
to us causing PCIe errors. Inhibit us performing any
operation on the MSI-X unless the MEMORY bit is set.

Note that Xen hypervisor with:
"x86/MSI-X: access MSI-X table only after having enabled MSI-X"
will return:
xen_pciback: 0000:0a:00.1: error -6 enabling MSI-X for guest 3!

When the generic MSI code tries to setup the PIRQ without
MEMORY bit set. Which means with later versions of Xen
(4.6) this patch is not neccessary.

This is part of XSA-157

Reviewed-by: Jan Beulich <jbeulich at suse.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/xen/xen-pciback/pciback_ops.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/xen-pciback/pciback_ops.c b/drivers/xen/xen-pciback/pciback_ops.c
index 539bc82..f64b7f5 100644
--- a/drivers/xen/xen-pciback/pciback_ops.c
+++ b/drivers/xen/xen-pciback/pciback_ops.c
@@ -212,6 +212,7 @@ int xen_pcibk_enable_msix(struct xen_pcibk_device *pdev,
 	struct xen_pcibk_dev_data *dev_data;
 	int i, result;
 	struct msix_entry *entries;
+	u16 cmd;

 	if (unlikely(verbose_request))
 		printk(KERN_DEBUG DRV_NAME ": %s: enable MSI-X\n",
@@ -223,7 +224,12 @@ int xen_pcibk_enable_msix(struct xen_pcibk_device *pdev,
 	if (dev->msix_enabled)
 		return -EALREADY;

-	if (dev->msi_enabled)
+	/*
+	 * PCI_COMMAND_MEMORY must be enabled, otherwise we may not be able
+	 * to access the BARs where the MSI-X entries reside.
+	 */
+	pci_read_config_word(dev, PCI_COMMAND, &cmd);
+	if (dev->msi_enabled || !(cmd & PCI_COMMAND_MEMORY))
 		return -ENXIO;

 	entries = kmalloc(op->value * sizeof(*entries), GFP_KERNEL);
--
1.9.1