3.16.51-rc1 review patch. If anyone has any objections, please let me know.
------------------ From: Martin Schwidefsky <[email protected]> commit 60f07c8ec5fae06c23e9fd7bab67dabce92b3414 upstream. The order in __tlb_flush_mm_lazy is to flush TLB first and then clear the mm->context.flush_mm bit. This can lead to missed flushes as the bit can be set anytime, the order needs to be the other way aronud. But this leads to a different race, __tlb_flush_mm_lazy may be called on two CPUs concurrently. If mm->context.flush_mm is cleared first then another CPU can bypass __tlb_flush_mm_lazy although the first CPU has not done the flush yet. In a virtualized environment the time until the flush is finally completed can be arbitrarily long. Add a spinlock to serialize __tlb_flush_mm_lazy and use the function in finish_arch_post_lock_switch as well. Reviewed-by: Heiko Carstens <[email protected]> Signed-off-by: Martin Schwidefsky <[email protected]> [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings <[email protected]> --- arch/s390/include/asm/mmu.h | 2 ++ arch/s390/include/asm/mmu_context.h | 4 ++-- arch/s390/include/asm/tlbflush.h | 4 +++- 3 files changed, 7 insertions(+), 3 deletions(-) --- a/arch/s390/include/asm/mmu.h +++ b/arch/s390/include/asm/mmu.h @@ -5,6 +5,7 @@ #include <linux/errno.h> typedef struct { + spinlock_t lock; cpumask_t cpu_attach_mask; atomic_t attach_count; unsigned int flush_mm; @@ -21,6 +22,7 @@ typedef struct { } mm_context_t; #define INIT_MM_CONTEXT(name) \ + .context.lock = __SPIN_LOCK_UNLOCKED(name.context.lock), \ .context.list_lock = __SPIN_LOCK_UNLOCKED(name.context.list_lock), \ .context.pgtable_list = LIST_HEAD_INIT(name.context.pgtable_list), \ .context.gmap_list = LIST_HEAD_INIT(name.context.gmap_list), --- a/arch/s390/include/asm/mmu_context.h +++ b/arch/s390/include/asm/mmu_context.h @@ -15,6 +15,7 @@ static inline int init_new_context(struct task_struct *tsk, struct mm_struct *mm) { + spin_lock_init(&mm->context.lock); spin_lock_init(&mm->context.list_lock); INIT_LIST_HEAD(&mm->context.pgtable_list); INIT_LIST_HEAD(&mm->context.gmap_list); @@ -95,8 +96,7 @@ static inline void finish_arch_post_lock cpu_relax(); cpumask_set_cpu(smp_processor_id(), mm_cpumask(mm)); - if (mm->context.flush_mm) - __tlb_flush_mm(mm); + __tlb_flush_mm_lazy(mm); preempt_enable(); } set_fs(current->thread.mm_segment); --- a/arch/s390/include/asm/tlbflush.h +++ b/arch/s390/include/asm/tlbflush.h @@ -164,10 +164,12 @@ static inline void __tlb_flush_mm(struct static inline void __tlb_flush_mm_lazy(struct mm_struct * mm) { + spin_lock(&mm->context.lock); if (mm->context.flush_mm) { - __tlb_flush_mm(mm); mm->context.flush_mm = 0; + __tlb_flush_mm(mm); } + spin_unlock(&mm->context.lock); } /*
