s390/mm: use invalid asce instead of kernel asce

Create a region 3 page table which contains only invalid entries, and
use that via "s390_invalid_asce" instead of the kernel ASCE whenever
there is either
- no user address space available, e.g. during early startup
- as an intermediate ASCE when address spaces are switched

This makes sure that user space accesses in such situations are
guaranteed to fail.

Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
index 51def960a3dd..87a84fc59fc3 100644
--- a/arch/s390/include/asm/mmu_context.h
+++ b/arch/s390/include/asm/mmu_context.h
@@ -79,7 +79,7 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 	S390_lowcore.user_asce = next->context.asce;
 	cpumask_set_cpu(cpu, &next->context.cpu_attach_mask);
 	/* Clear previous user-ASCE from CR7 */
-	__ctl_load(S390_lowcore.kernel_asce, 7, 7);
+	__ctl_load(s390_invalid_asce, 7, 7);
 	if (prev != next)
 		cpumask_clear_cpu(cpu, &prev->context.cpu_attach_mask);
 }