[PATCH Xenial SRU] s390/mm: fix gmap tlb flush issues

[Tim Gardner]

From: David Hildenbrand <dahi at linux.vnet.ibm.com>

BugLink: http://bugs.launchpad.net/bugs/1634034

__tlb_flush_asce() should never be used if multiple asce belong to a mm.

As this function changes mm logic determining if local or global tlb
flushes will be neded, we might end up flushing only the gmap asce on all
CPUs and a follow up mm asce flushes will only flush on the local CPU,
although that asce ran on multiple CPUs.

The missing tlb flushes will provoke strange faults in user space and even
low address protections in user space, crashing the kernel.

Fixes: 1b948d6caec4 ("s390/mm,tlb: optimize TLB flushing for zEC12")
Cc: stable at vger.kernel.org # 3.15+
Reported-by: Sascha Silbe <silbe at linux.vnet.ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky at de.ibm.com>
Signed-off-by: David Hildenbrand <dahi at linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky at de.ibm.com>
(back ported from commit f045402984404ddc11016358411e445192919047)
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>

 Conflicts:
	arch/s390/mm/gmap.c
---
 arch/s390/include/asm/tlbflush.h | 3 ++-
 arch/s390/mm/pgtable.c           | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/s390/include/asm/tlbflush.h b/arch/s390/include/asm/tlbflush.h
index a2e6ef3..0a20316 100644
--- a/arch/s390/include/asm/tlbflush.h
+++ b/arch/s390/include/asm/tlbflush.h
@@ -81,7 +81,8 @@ static inline void __tlb_flush_full(struct mm_struct *mm)
 }
 
 /*
- * Flush TLB entries for a specific ASCE on all CPUs.
+ * Flush TLB entries for a specific ASCE on all CPUs. Should never be used
+ * when more than one asce (e.g. gmap) ran on this mm.
  */
 static inline void __tlb_flush_asce(struct mm_struct *mm, unsigned long asce)
 {
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 471a370..8345ae1 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -166,7 +166,7 @@ EXPORT_SYMBOL_GPL(gmap_alloc);
 static void gmap_flush_tlb(struct gmap *gmap)
 {
 	if (MACHINE_HAS_IDTE)
-		__tlb_flush_asce(gmap->mm, gmap->asce);
+		__tlb_flush_idte(gmap->asce);
 	else
 		__tlb_flush_global();
 }
@@ -205,7 +205,7 @@ void gmap_free(struct gmap *gmap)
 
 	/* Flush tlb. */
 	if (MACHINE_HAS_IDTE)
-		__tlb_flush_asce(gmap->mm, gmap->asce);
+		__tlb_flush_idte(gmap->asce);
 	else
 		__tlb_flush_global();
 
-- 
2.7.4