[MIPS] Handle I-cache coherency in flush_cache_range()

So far flush_cache_range() did't consider the I-cache largely because it
did rarely ever matter to real world code.  This was working primarily
because normally code and data are don't share the same pages - with the
exception of MIPS16 code which uses address constants embedded between
the code.   The following sequence of events may break the code:

 o MIPS16 executable being loaded
 o dynamic linker relocates the address constants embedded into the code:
 o   Uses mprotect(2) to make code pages PROT_READ|PROT_WRITE
 o   Performs the actual relocations by writing to the pages which likely
     are COW.  Because no PROT_EXEC is set I-cache coherence will not be
     considered.
 o   Uses mprotect(2) to switch code pages back to PROT_READ|PROT_EXEC.
     This results in a call to flush_cache_range() which also does not
     consider I-caches.
 o => executing the page just having been relocated may now result in the
   I-cache getting refilled with stale data from memory.
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/mm/c-r4k.c

@@ -364,20 +364,23 @@ static inline int has_valid_asid(const struct mm_struct *mm)
 static inline void local_r4k_flush_cache_range(void * args)
 {
 	struct vm_area_struct *vma = args;
+	int exec = vma->vm_flags & VM_EXEC;
 
 	if (!(has_valid_asid(vma->vm_mm)))
 		return;
 
 	r4k_blast_dcache();
+	if (exec)
+		r4k_blast_icache();
 }
 
 static void r4k_flush_cache_range(struct vm_area_struct *vma,
 	unsigned long start, unsigned long end)
 {
-	if (!cpu_has_dc_aliases)
-		return;
+	int exec = vma->vm_flags & VM_EXEC;
 
-	r4k_on_each_cpu(local_r4k_flush_cache_range, vma, 1, 1);
+	if (cpu_has_dc_aliases || (exec && !cpu_has_ic_fills_f_dc))
+		r4k_on_each_cpu(local_r4k_flush_cache_range, vma, 1, 1);
 }
 
 static inline void local_r4k_flush_cache_mm(void * args)