Contain MSI errors in msi emulation code

If msi=0 is specified and guest want to enable msi, qemu finds it can
not enable it and quits.  (This problem is not appicable for xen
unstable since the "msi=x" switch is removed.)  This patch let these
cases be handled inside msi emulation code. If qemu can not enable
msi, guest will not receive MSI.  But Qemu can still go on.  But if
guest driver does not test MSI's functionality, guest device will stop
to function.

Submitted-By: Haitao Shan
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
(cherry picked from commit 35f55c5b0b54e310c787c39bde0f723a1390e839)

Cherry pick requested by Dexuan Cui:
 In the latest Xen-unstable, MSI in xen was disabled temporarily and
 many guests with MSI-capable NIC assigned fail to bootup.  Could you
 please pull the following commit of qemu-xen-3.3-testing.git into
 qemu-xen-unstable.git?

Conflicts:
	hw/pass-through.c

diff --git a/hw/pass-through.c b/hw/pass-through.c
index 7280677f4cb55847a7cf23a734f30b2ef2df6a4e..6cf63e6f3084d9aa6a694e8817103137082535dc 100644 (file)
--- a/hw/pass-through.c
+++ b/hw/pass-through.c
@@ -2800,8 +2800,14 @@ static int pt_msgctrl_reg_write(struct pt_dev *ptdev,
                 PT_LOG("setup msi for dev %x\n", pd->devfn);
                 if (pt_msi_setup(ptdev))
                 {
-                    PT_LOG("pt_msi_setup error!!!\n");
-                    return -1;
+                   /* We do not broadcast the error to the framework code, so
+                    * that MSI errors are contained in MSI emulation code and
+                    * QEMU can go on running.
+                    * Guest MSI would be actually not working.
+                    */
+                   *value &= ~PCI_MSI_FLAGS_ENABLE;
+                   PT_LOG("Warning: Can not map MSI for dev %x\n", pd->devfn);
+                   return 0;
                 }
             }
             pt_msi_update(ptdev);