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>

diff --git a/xen/arch/x86/msi.c b/xen/arch/x86/msi.c
index 77998f4fb31421f4f1c1d13c7ffe6837493a4ad1..4652b98c2d95c63653a0f36fbfd17c06c5cc4953 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);