MIPS: tlb-r4k: Add missing HTW stop/start sequences

HTW needs to stop and start again whenever the EntryHI register
changes otherwise an inflight HTW operation might use the new
EntryHI register for updating an old entry and that could lead
to crashes or even a machine check exception. We fix this by
ensuring the HTW has stop whenever the EntryHI register is about
to change

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: <stable@vger.kernel.org> # v3.17+
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8511/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/mm/tlb-r4k.c

@@ -299,6 +299,7 @@ void __update_tlb(struct vm_area_struct * vma, unsigned long address, pte_t pte)
 
 	local_irq_save(flags);
 
+	htw_stop();
 	pid = read_c0_entryhi() & ASID_MASK;
 	address &= (PAGE_MASK << 1);
 	write_c0_entryhi(address | pid);
@@ -346,6 +347,7 @@ void __update_tlb(struct vm_area_struct * vma, unsigned long address, pte_t pte)
 			tlb_write_indexed();
 	}
 	tlbw_use_hazard();
+	htw_start();
 	flush_itlb_vm(vma);
 	local_irq_restore(flags);
 }
@@ -422,6 +424,7 @@ __init int add_temporary_entry(unsigned long entrylo0, unsigned long entrylo1,
 
 	local_irq_save(flags);
 	/* Save old context and create impossible VPN2 value */
+	htw_stop();
 	old_ctx = read_c0_entryhi();
 	old_pagemask = read_c0_pagemask();
 	wired = read_c0_wired();
@@ -443,6 +446,7 @@ __init int add_temporary_entry(unsigned long entrylo0, unsigned long entrylo1,
 
 	write_c0_entryhi(old_ctx);
 	write_c0_pagemask(old_pagemask);
+	htw_start();
 out:
 	local_irq_restore(flags);
 	return ret;