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From 6f2a8ff9967b2e5ba4cea5eb9067f794e8e690bf Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Tue, 26 Mar 2019 18:31:54 +0100
Subject: [PATCH] powerpc/pseries/iommu: Use a locallock instead
 local_irq_save()

References: SLE Realtime Extension
Patch-mainline: Queued in subsystem maintainer repository
Git-commit: c8cd18016799bbb5af51b5e5e0c2bdf0813d58e5
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git

The locallock protects the per-CPU variable tce_page. The function
attempts to allocate memory while tce_page is protected (by disabling
interrupts).

Use local_irq_save() instead of local_irq_disable().

Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 arch/powerpc/platforms/pseries/iommu.c | 31 ++++++++++++++++++++-----------
 1 file changed, 20 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
index 77735306d5f1..09f5df149cdf 100644
--- a/arch/powerpc/platforms/pseries/iommu.c
+++ b/arch/powerpc/platforms/pseries/iommu.c
@@ -24,6 +24,7 @@
 #include <linux/of.h>
 #include <linux/iommu.h>
 #include <linux/rculist.h>
+#include <linux/local_lock.h>
 #include <asm/io.h>
 #include <asm/prom.h>
 #include <asm/rtas.h>
@@ -190,7 +191,13 @@ static int tce_build_pSeriesLP(unsigned long liobn, long tcenum, long tceshift,
 	return ret;
 }
 
-static DEFINE_PER_CPU(__be64 *, tce_page);
+struct tce_page {
+	__be64 * page;
+	local_lock_t lock;
+};
+static DEFINE_PER_CPU(struct tce_page, tce_page) = {
+	.lock = INIT_LOCAL_LOCK(lock),
+};
 
 static int tce_buildmulti_pSeriesLP(struct iommu_table *tbl, long tcenum,
 				     long npages, unsigned long uaddr,
@@ -212,9 +219,10 @@ static int tce_buildmulti_pSeriesLP(struct iommu_table *tbl, long tcenum,
 		                           direction, attrs);
 	}
 
-	local_irq_save(flags);	/* to protect tcep and the page behind it */
+	/* to protect tcep and the page behind it */
+	local_lock_irqsave(&tce_page.lock, flags);
 
-	tcep = __this_cpu_read(tce_page);
+	tcep = __this_cpu_read(tce_page.page);
 
 	/* This is safe to do since interrupts are off when we're called
 	 * from iommu_alloc{,_sg}()
@@ -223,12 +231,12 @@ static int tce_buildmulti_pSeriesLP(struct iommu_table *tbl, long tcenum,
 		tcep = (__be64 *)__get_free_page(GFP_ATOMIC);
 		/* If allocation fails, fall back to the loop implementation */
 		if (!tcep) {
-			local_irq_restore(flags);
+			local_unlock_irqrestore(&tce_page.lock, flags);
 			return tce_build_pSeriesLP(tbl->it_index, tcenum,
 					tceshift,
 					npages, uaddr, direction, attrs);
 		}
-		__this_cpu_write(tce_page, tcep);
+		__this_cpu_write(tce_page.page, tcep);
 	}
 
 	rpn = __pa(uaddr) >> tceshift;
@@ -258,7 +266,7 @@ static int tce_buildmulti_pSeriesLP(struct iommu_table *tbl, long tcenum,
 		tcenum += limit;
 	} while (npages > 0 && !rc);
 
-	local_irq_restore(flags);
+	local_unlock_irqrestore(&tce_page.lock, flags);
 
 	if (unlikely(rc == H_NOT_ENOUGH_RESOURCES)) {
 		ret = (int)rc;
@@ -429,16 +437,17 @@ static int tce_setrange_multi_pSeriesLP(unsigned long start_pfn,
 				DMA_BIDIRECTIONAL, 0);
 	}
 
-	local_irq_disable();	/* to protect tcep and the page behind it */
-	tcep = __this_cpu_read(tce_page);
+	/* to protect tcep and the page behind it */
+	local_lock_irq(&tce_page.lock);
+	tcep = __this_cpu_read(tce_page.page);
 
 	if (!tcep) {
 		tcep = (__be64 *)__get_free_page(GFP_ATOMIC);
 		if (!tcep) {
-			local_irq_enable();
+			local_unlock_irq(&tce_page.lock);
 			return -ENOMEM;
 		}
-		__this_cpu_write(tce_page, tcep);
+		__this_cpu_write(tce_page.page, tcep);
 	}
 
 	proto_tce = TCE_PCI_READ | TCE_PCI_WRITE;
@@ -481,7 +490,7 @@ static int tce_setrange_multi_pSeriesLP(unsigned long start_pfn,
 
 	/* error cleanup: caller will clear whole range */
 
-	local_irq_enable();
+	local_unlock_irq(&tce_page.lock);
 	return rc;
 }