x86/MSI: disallow redundant enabling

At the moment, Xen attempts to allow redundant enabling of MSI by
having pci_enable_msi() return 0, and point to the existing MSI
descriptor, when the msi already exists.

Unfortunately, if subsequent errors are encountered, the cleanup
paths assume pci_enable_msi() had done full initialization, and
hence undo everything that was assumed to be done by that
function without also undoing other setup that would normally
occur only after that function was called (in map_domain_pirq()
itself).

Rather than try to make the redundant enabling case work properly, just
forbid it entirely by having pci_enable_msi() return -EEXIST when MSI
is already set up.

This is part of XSA-237.

Reported-by: HW42 <hw42@ipsumj.de>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>
master commit: a46126fec20e0cf4f5442352ef45efaea8c89646
master date: 2017-10-12 14:36:58 +0200

diff --git a/xen/arch/x86/msi.c b/xen/arch/x86/msi.c
index d98f4006996541254c9339a5c8ac1f7583cbc8d9..f06f6ab5130ab617545122520cb4c0b36b5f84c2 100644 (file)
--- a/xen/arch/x86/msi.c
+++ b/xen/arch/x86/msi.c
@@ -1050,11 +1050,10 @@ static int __pci_enable_msi(struct msi_info *msi, struct msi_desc **desc)
     old_desc = find_msi_entry(pdev, msi->irq, PCI_CAP_ID_MSI);
     if ( old_desc )
     {
-        printk(XENLOG_WARNING "irq %d already mapped to MSI on %04x:%02x:%02x.%u\n",
+        printk(XENLOG_ERR "irq %d already mapped to MSI on %04x:%02x:%02x.%u\n",
                msi->irq, msi->seg, msi->bus,
                PCI_SLOT(msi->devfn), PCI_FUNC(msi->devfn));
-        *desc = old_desc;
-        return 0;
+        return -EEXIST;
     }
 
     old_desc = find_msi_entry(pdev, -1, PCI_CAP_ID_MSIX);
@@ -1118,11 +1117,10 @@ static int __pci_enable_msix(struct msi_info *msi, struct msi_desc **desc)
     old_desc = find_msi_entry(pdev, msi->irq, PCI_CAP_ID_MSIX);
     if ( old_desc )
     {
-        printk(XENLOG_WARNING "irq %d already mapped to MSI-X on %04x:%02x:%02x.%u\n",
+        printk(XENLOG_ERR "irq %d already mapped to MSI-X on %04x:%02x:%02x.%u\n",
                msi->irq, msi->seg, msi->bus,
                PCI_SLOT(msi->devfn), PCI_FUNC(msi->devfn));
-        *desc = old_desc;
-        return 0;
+        return -EEXIST;
     }
 
     old_desc = find_msi_entry(pdev, -1, PCI_CAP_ID_MSI);