[PATCH 4.13 084/109] s390/mm: fix local TLB flushing vs. detach of an mm address space

Greg Kroah-Hartman
2017-09-24T20:43:25Z

From: Martin Schwidefsky <schwidefsky@de.ibm.com>

commit b3e5dc45fd1ec2aa1de6b80008f9295eb17e0659 upstream.

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.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/s390/include/asm/mmu_context.h | 4 ++--
arch/s390/include/asm/tlbflush.h | 26 +++++---------------------
2 files changed, 7 insertions(+), 23 deletions(-)

--- a/arch/s390/include/asm/mmu_context.h
+++ b/arch/s390/include/asm/mmu_context.h
@@ -102,7 +102,6 @@ static inline void switch_mm(struct mm_s
if (prev == next)
return;
cpumask_set_cpu(cpu, &next->context.cpu_attach_mask);
- cpumask_set_cpu(cpu, mm_cpumask(next));
/* Clear old ASCE by loading the kernel ASCE. */
__ctl_load(S390_lowcore.kernel_asce, 1, 1);
__ctl_load(S390_lowcore.kernel_asce, 7, 7);
@@ -120,7 +119,7 @@ static inline void finish_arch_post_lock
preempt_disable();
while (atomic_read(&mm->context.flush_count))
cpu_relax();
-
+ cpumask_set_cpu(smp_processor_id(), mm_cpumask(mm));
if (mm->context.flush_mm)
__tlb_flush_mm(mm);
preempt_enable();
@@ -135,6 +134,7 @@ static inline void activate_mm(struct mm
struct mm_struct *next)
{
switch_mm(prev, next, current);
+ cpumask_set_cpu(smp_processor_id(), mm_cpumask(next));
set_user_asce(next);
}

--- a/arch/s390/include/asm/tlbflush.h
+++ b/arch/s390/include/asm/tlbflush.h
@@ -43,23 +43,6 @@ static inline void __tlb_flush_global(vo
* 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;
@@ -71,16 +54,18 @@ static inline void __tlb_flush_mm(struct
*/
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();
}
@@ -94,7 +79,6 @@ static inline void __tlb_flush_kernel(vo
}
#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.