pseries/iommu: Ensure TCEs are cleared with non-huge DDW

There are now two kinds of DMA windows that might be presented by
PowerVM DDW support -- huge windows (that can map all of system memory
regardless of the LPAR configuration) and non-huge windows (which
can't). They are implemented slightly differently in PowerVM, and thus
have different characteristics. The most obvious is that slot isolate
doesn't clear the TCEs/window for us with non-huge windows. Thus, when a
DLPAR operation occurs on a slot using a non-huge window, TCEs are still
present (the notifier chain doesn't currently remove them explicitly)
and the DLPAR fails. Fix this by calling remove_ddw() first, which will
unmap the DDW TCEs.

Note: a corresponding change to drmgr is needed to actually successfully
DLPAR, such that the device-tree update (which causes the notifier chain
to fire) occurs before slot isolate.
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/pseries/iommu.c

@@ -1296,6 +1296,7 @@ static int iommu_reconfig_notifier(struct notifier_block *nb, unsigned long acti
 
 	switch (action) {
 	case OF_RECONFIG_DETACH_NODE:
+		remove_ddw(np);
 		if (pci && pci->iommu_table)
 			iommu_free_table(pci->iommu_table, np->full_name);
 
@@ -1308,16 +1309,6 @@ static int iommu_reconfig_notifier(struct notifier_block *nb, unsigned long acti
 			}
 		}
 		spin_unlock(&direct_window_list_lock);
-
-		/*
-		 * Because the notifier runs after isolation of the
-		 * slot, we are guaranteed any DMA window has already
-		 * been revoked and the TCEs have been marked invalid,
-		 * so we don't need a call to remove_ddw(np). However,
-		 * if an additional notifier action is added before the
-		 * isolate call, we should update this code for
-		 * completeness with such a call.
-		 */
 		break;
 	default:
 		err = NOTIFY_DONE;