[PATCH 3.12 54/58] xen/pciback: Return error on XEN_PCI_OP_enable_msix when device has MSI or MSI-X enabled

From: Konrad Rzeszutek Wilk 3.12-stable review patch. If anyone has any objections, please let me know. === commit 5e0ce1455c09dd61d029b8ad45d82e1ac0b6c4c9 upstream. The guest sequence of: a) XEN_PCI_OP_enable_msix b) XEN_PCI_OP_enable_msix results

[PATCH 3.12 54/58] xen/pciback: Return error on XEN_PCI_OP_enable_msix when device has MSI or MSI-X enabled

From: Konrad Rzeszutek Wilk 3.12-stable review patch. If anyone has any objections, please let me know. === commit 5e0ce1455c09dd61d029b8ad45d82e1ac0b6c4c9 upstream. The guest sequence of: a) XEN_PCI_OP_enable_msix b) XEN_PCI_OP_enable_msix results in hitting an NULL