[PATCH] vpci/msix: exit early if MSI-X is disabled

[Roger Pau Monne <roger.pau@citrix.com>]

Do not attempt to mask an MSI-X entry if MSI-X is not enabled. Else it
will lead to hitting the following assert on debug builds:

(XEN) Panic on CPU 13:
(XEN) Assertion 'entry->arch.pirq != INVALID_PIRQ' failed at vmsi.c:843

In order to fix it exit early from the switch in msix_write if MSI-X
is not enabled.

Fixes: d6281be9d0145 ('vpci/msix: add MSI-X handlers')
Reported-by: Manuel Bouyer <bouyer@antioche.eu.org>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
 xen/drivers/vpci/msix.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/xen/drivers/vpci/msix.c b/xen/drivers/vpci/msix.c
index 64dd0a929c..93902ba7db 100644
--- a/xen/drivers/vpci/msix.c
+++ b/xen/drivers/vpci/msix.c
@@ -357,7 +357,11 @@ static int msix_write(struct vcpu *v, unsigned long addr, unsigned int len,
          * so that it picks the new state.
          */
         entry->masked = new_masked;
-        if ( !new_masked && msix->enabled && !msix->masked && entry->updated )
+
+        if ( !msix->enabled )
+            break;
+
+        if ( !new_masked && !msix->masked && entry->updated )
         {
             /*
              * If MSI-X is enabled, the function mask is not active, the entry
-- 
2.29.2