asm-generic/tlb: avoid potential double flush

Aneesh reported that:

	tlb_flush_mmu()
	  tlb_flush_mmu_tlbonly()
	    tlb_flush()			<-- #1
	  tlb_flush_mmu_free()
	    tlb_table_flush()
	      tlb_table_invalidate()
		tlb_flush_mmu_tlbonly()
		  tlb_flush()		<-- #2

does two TLBIs when tlb->fullmm, because __tlb_reset_range() will not
clear tlb->end in that case.

Observe that any caller to __tlb_adjust_range() also sets at least one of
the tlb->freed_tables || tlb->cleared_p* bits, and those are
unconditionally cleared by __tlb_reset_range().

Change the condition for actually issuing TLBI to having one of those bits
set, as opposed to having tlb->end != 0.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Aneesh Kumar K.V <[email protected]>
Reported-by: "Aneesh Kumar K.V" <[email protected]>
Cc: Michael Ellerman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/asm-generic/tlb.h

@@ -402,7 +402,12 @@ tlb_update_vma_flags(struct mmu_gather *tlb, struct vm_area_struct *vma) { }
 
 static inline void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb)
 {
-	if (!tlb->end)
+	/*
+	 * Anything calling __tlb_adjust_range() also sets at least one of
+	 * these bits.
+	 */
+	if (!(tlb->freed_tables || tlb->cleared_ptes || tlb->cleared_pmds ||
+	      tlb->cleared_puds || tlb->cleared_p4ds))
 		return;
 
 	tlb_flush(tlb);