s390/mm: fix local TLB flushing vs. detach of an mm address space

The local TLB flushing code keeps an additional mask in the mm.context,
the cpu_attach_mask. At the time a global flush of an address space is
done the cpu_attach_mask is copied to the mm_cpumask in order to avoid
future global flushes in case the mm is used by a single CPU only after
the flush.

Trouble is that the reset of the mm_cpumask is racy against the detach
of an mm address space by switch_mm. The current order is first the
global TLB flush and then the copy of the cpu_attach_mask to the
mm_cpumask. The order needs to be the other way around.

Cc: <stable@vger.kernel.org>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 5 insertions, 21 deletions

diff --git a/arch/s390/include/asm/tlbflush.h b/arch/s390/include/asm/tlbflush.h
index 4d759f8f4bc7..16fe2a3d9a03 100644
--- a/arch/s390/include/asm/tlbflush.h
+++ b/arch/s390/include/asm/tlbflush.h
@@ -48,23 +48,6 @@ static inline void __tlb_flush_global(void)
  * Flush TLB entries for a specific mm on all CPUs (in case gmap is used
  * this implicates multiple ASCEs!).
  */
-static inline void __tlb_flush_full(struct mm_struct *mm)
-{
-	preempt_disable();
-	atomic_inc(&mm->context.flush_count);
-	if (cpumask_equal(mm_cpumask(mm), cpumask_of(smp_processor_id()))) {
-		/* Local TLB flush */
-		__tlb_flush_local();
-	} else {
-		/* Global TLB flush */
-		__tlb_flush_global();
-		/* Reset TLB flush mask */
-		cpumask_copy(mm_cpumask(mm), &mm->context.cpu_attach_mask);
-	}
-	atomic_dec(&mm->context.flush_count);
-	preempt_enable();
-}
-
 static inline void __tlb_flush_mm(struct mm_struct *mm)
 {
 	unsigned long gmap_asce;
@@ -76,16 +59,18 @@ static inline void __tlb_flush_mm(struct mm_struct *mm)
 	 */
 	preempt_disable();
 	atomic_inc(&mm->context.flush_count);
+	/* Reset TLB flush mask */
+	cpumask_copy(mm_cpumask(mm), &mm->context.cpu_attach_mask);
+	barrier();
 	gmap_asce = READ_ONCE(mm->context.gmap_asce);
 	if (MACHINE_HAS_IDTE && gmap_asce != -1UL) {
 		if (gmap_asce)
 			__tlb_flush_idte(gmap_asce);
 		__tlb_flush_idte(mm->context.asce);
 	} else {
-		__tlb_flush_full(mm);
+		/* Global TLB flush */
+		__tlb_flush_global();
 	}
-	/* Reset TLB flush mask */
-	cpumask_copy(mm_cpumask(mm), &mm->context.cpu_attach_mask);
 	atomic_dec(&mm->context.flush_count);
 	preempt_enable();
 }
@@ -99,7 +84,6 @@ static inline void __tlb_flush_kernel(void)
 }
 #else
 #define __tlb_flush_global()	__tlb_flush_local()
-#define __tlb_flush_full(mm)	__tlb_flush_local()
 
 /*
  * Flush TLB entries for a specific ASCE on all CPUs.