powerpc/pseries: Disable interrupts around IOMMU percpu data accesses

tce_buildmulti_pSeriesLP uses a per cpu page to communicate with the
hypervisor. We currently rely on the IOMMU table spinlock but
subsequent patches will be removing that so disable interrupts
around all accesses of tce_page.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/pseries/iommu.c

@@ -192,12 +192,15 @@ static int tce_buildmulti_pSeriesLP(struct iommu_table *tbl, long tcenum,
 	long l, limit;
 	long tcenum_start = tcenum, npages_start = npages;
 	int ret = 0;
+	unsigned long flags;
 
 	if (npages == 1) {
 		return tce_build_pSeriesLP(tbl, tcenum, npages, uaddr,
 		                           direction, attrs);
 	}
 
+	local_irq_save(flags);	/* to protect tcep and the page behind it */
+
 	tcep = __get_cpu_var(tce_page);
 
 	/* This is safe to do since interrupts are off when we're called
@@ -207,6 +210,7 @@ static int tce_buildmulti_pSeriesLP(struct iommu_table *tbl, long tcenum,
 		tcep = (u64 *)__get_free_page(GFP_ATOMIC);
 		/* If allocation fails, fall back to the loop implementation */
 		if (!tcep) {
+			local_irq_restore(flags);
 			return tce_build_pSeriesLP(tbl, tcenum, npages, uaddr,
 					    direction, attrs);
 		}
@@ -240,6 +244,8 @@ static int tce_buildmulti_pSeriesLP(struct iommu_table *tbl, long tcenum,
 		tcenum += limit;
 	} while (npages > 0 && !rc);
 
+	local_irq_restore(flags);
+
 	if (unlikely(rc == H_NOT_ENOUGH_RESOURCES)) {
 		ret = (int)rc;
 		tce_freemulti_pSeriesLP(tbl, tcenum_start,