s390/uaccess: always load the kernel ASCE after task switch

This patch fixes a problem introduced with git commit beef560b4cdfafb2
"s390/uaccess: simplify control register updates".

The switch_mm function is not called if the next process is a kernel
thread without an attached mm or is a nop if the mm does not change.
But CR1 still needs to be loaded with the kernel ASCE in case the
code returns to a uaccess function that uses the secondary space mode.

In addition move the set_fs call from finish_arch_switch to
finish_arch_post_lock_switch and then remove finish_arch_switch.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

2 files changed, 16 insertions, 21 deletions

diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
index c28f32a45af5..3815bfea1b2d 100644
--- a/arch/s390/include/asm/mmu_context.h
+++ b/arch/s390/include/asm/mmu_context.h
@@ -33,10 +33,9 @@ static inline int init_new_context(struct task_struct *tsk,
 
 static inline void set_user_asce(struct mm_struct *mm)
 {
-        pgd_t *pgd = mm->pgd;
-
-        S390_lowcore.user_asce = mm->context.asce_bits | __pa(pgd);
-        set_fs(current->thread.mm_segment);
+        S390_lowcore.user_asce = mm->context.asce_bits | __pa(mm->pgd);
+        if (current->thread.mm_segment.ar4)
+                __ctl_load(S390_lowcore.user_asce, 7, 7);
         set_cpu_flag(CIF_ASCE);
 }
 
@@ -70,12 +69,11 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *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);
-        /* Delay loading of the new ASCE to control registers CR1 & CR7 */
-        set_cpu_flag(CIF_ASCE);
         atomic_inc(&next->context.attach_count);
         atomic_dec(&prev->context.attach_count);
         if (MACHINE_HAS_TLB_LC)
                 cpumask_clear_cpu(cpu, &prev->context.cpu_attach_mask);
+        S390_lowcore.user_asce = next->context.asce_bits | __pa(next->pgd);
 }
 
 #define finish_arch_post_lock_switch finish_arch_post_lock_switch
@@ -84,17 +82,18 @@ static inline void finish_arch_post_lock_switch(void)
         struct task_struct *tsk = current;
         struct mm_struct *mm = tsk->mm;
 
-        if (!mm)
-                return;
-        preempt_disable();
-        while (atomic_read(&mm->context.attach_count) >> 16)
-                cpu_relax();
-
-        cpumask_set_cpu(smp_processor_id(), mm_cpumask(mm));
-        set_user_asce(mm);
-        if (mm->context.flush_mm)
-                __tlb_flush_mm(mm);
-        preempt_enable();
+        load_kernel_asce();
+        if (mm) {
+                preempt_disable();
+                while (atomic_read(&mm->context.attach_count) >> 16)
+                        cpu_relax();
+
+                cpumask_set_cpu(smp_processor_id(), mm_cpumask(mm));
+                if (mm->context.flush_mm)
+                        __tlb_flush_mm(mm);
+                preempt_enable();
+        }
+        set_fs(current->thread.mm_segment);
 }
 
 #define enter_lazy_tlb(mm,tsk)  do { } while (0)
diff --git a/arch/s390/include/asm/switch_to.h b/arch/s390/include/asm/switch_to.h
index 29c81f82705e..df38c70cd59e 100644
--- a/arch/s390/include/asm/switch_to.h
+++ b/arch/s390/include/asm/switch_to.h
@@ -134,8 +134,4 @@ static inline void restore_access_regs(unsigned int *acrs)
         prev = __switch_to(prev,next);                                  \
 } while (0)
 
-#define finish_arch_switch(prev) do {                                        \
-        set_fs(current->thread.mm_segment);                                  \
-} while (0)
-
 #endif /* __ASM_SWITCH_TO_H */