[MIPS] Do not use drop_mmu_context to flusing other task's VIPT I-cache.

c-r4k.c and c-sb1.c use drop_mmu_context() to flush virtually tagged
I-caches, but this does not work for flushing other task's icache.  This
is for example triggered by copy_to_user_page() called from ptrace(2).
Use indexed flush for such cases.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/mm/c-r4k.c

@@ -475,7 +475,7 @@ static inline void local_r4k_flush_cache_page(void *args)
 		}
 	}
 	if (exec) {
-		if (cpu_has_vtag_icache) {
+		if (cpu_has_vtag_icache && mm == current->active_mm) {
 			int cpu = smp_processor_id();
 
 			if (cpu_context(cpu, mm) != 0)
@@ -599,7 +599,7 @@ static inline void local_r4k_flush_icache_page(void *args)
 	 * We're not sure of the virtual address(es) involved here, so
 	 * we have to flush the entire I-cache.
 	 */
-	if (cpu_has_vtag_icache) {
+	if (cpu_has_vtag_icache && vma->vm_mm == current->active_mm) {
 		int cpu = smp_processor_id();
 
 		if (cpu_context(cpu, vma->vm_mm) != 0)