RE: [Xen-devel] About VT-d on ASUS P6T

["Han, Weidong" <weidong.han@xxxxxxxxx>]

Your code changes just let xen not disable VT-d, but actually 
"iommu=passthrough" avoids problems of incorrect RMRR. This option makes dom0 
not use VT-d, therefore incorrect RMRR won't be used by device. But if you 
assign the device whose RMRR incorrect to guest, it still causes problems. 

Regards,
Weidong

-----Original Message-----
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Felix Kuperjans
Sent: Tuesday, May 11, 2010 6:09 PM
To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] About VT-d on ASUS P6T

Hi,

as I posted on xen-users, I've successfully used pci passtrough on an ASUS P6T 
mainboard which is known to have really buggy RMRR tables.

I needed the iommu=passtrough and iommu_inclusive_mapping=1 command line 
options, combined with a little change to the RMRR parsing code:

dmar.c:

@@ -559,8 +558,7 @@
             dprintk(XENLOG_WARNING VTDPREFIX,
                 "  The RMRR (%"PRIx64", %"PRIx64") is incorrect!\n",
                 rmrru->base_address, rmrru->end_address);
-            xfree(rmrru);
-            ret = -EFAULT;
+            acpi_register_rmrr_unit(rmrru);
         }
         else
         {

This way, the condition that causes the error printed above, does not lead to 
an abortion of VT-d code, but instead registers the RMRR unit as if it was 
correct.
VT-d is working properly afterwards and I've tested some devices successfully.

Probably, you would prefer to choose the action based on some command line 
option (like iommu_inclusive_mapping=1) instead of ignoring this error by 
default.

Regards,
Felix


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