powerpc/mm/hash: Reduce contention on hpte lock

We do this in some part. This patch make sure we always try to search
for hpte without holding lock and redo the compare with lock held once
match found.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/hash_native_64.c

@@ -568,23 +568,26 @@ static void native_hpte_invalidate(unsigned long slot, unsigned long vpn,
 	DBG_LOW("    invalidate(vpn=%016lx, hash: %lx)\n", vpn, slot);
 
 	want_v = hpte_encode_avpn(vpn, bpsize, ssize);
-	native_lock_hpte(hptep);
 	hpte_v = hpte_get_old_v(hptep);
 
+	if (HPTE_V_COMPARE(hpte_v, want_v) && (hpte_v & HPTE_V_VALID)) {
+		native_lock_hpte(hptep);
+		/* recheck with locks held */
+		hpte_v = hpte_get_old_v(hptep);
+
+		if (HPTE_V_COMPARE(hpte_v, want_v) && (hpte_v & HPTE_V_VALID))
+			/* Invalidate the hpte. NOTE: this also unlocks it */
+			hptep->v = 0;
+		else
+			native_unlock_hpte(hptep);
+	}
 	/*
 	 * We need to invalidate the TLB always because hpte_remove doesn't do
 	 * a tlb invalidate. If a hash bucket gets full, we "evict" a more/less
 	 * random entry from it. When we do that we don't invalidate the TLB
 	 * (hpte_remove) because we assume the old translation is still
 	 * technically "valid".
 	 */
-	if (!HPTE_V_COMPARE(hpte_v, want_v) || !(hpte_v & HPTE_V_VALID))
-		native_unlock_hpte(hptep);
-	else
-		/* Invalidate the hpte. NOTE: this also unlocks it */
-		hptep->v = 0;
-
-	/* Invalidate the TLB */
 	tlbie(vpn, bpsize, apsize, ssize, local);
 
 	local_irq_restore(flags);
@@ -626,15 +629,23 @@ static void native_hugepage_invalidate(unsigned long vsid,
 
 		hptep = htab_address + slot;
 		want_v = hpte_encode_avpn(vpn, psize, ssize);
-		native_lock_hpte(hptep);
 		hpte_v = hpte_get_old_v(hptep);
 
 		/* Even if we miss, we need to invalidate the TLB */
-		if (!HPTE_V_COMPARE(hpte_v, want_v) || !(hpte_v & HPTE_V_VALID))
-			native_unlock_hpte(hptep);
-		else
-			/* Invalidate the hpte. NOTE: this also unlocks it */
-			hptep->v = 0;
+		if (HPTE_V_COMPARE(hpte_v, want_v) && (hpte_v & HPTE_V_VALID)) {
+			/* recheck with locks held */
+			native_lock_hpte(hptep);
+			hpte_v = hpte_get_old_v(hptep);
+
+			if (HPTE_V_COMPARE(hpte_v, want_v) && (hpte_v & HPTE_V_VALID)) {
+				/*
+				 * Invalidate the hpte. NOTE: this also unlocks it
+				 */
+
+				hptep->v = 0;
+			} else
+				native_unlock_hpte(hptep);
+		}
 		/*
 		 * We need to do tlb invalidate for all the address, tlbie
 		 * instruction compares entry_VA in tlb with the VA specified
@@ -802,13 +813,19 @@ static void native_flush_hash_range(unsigned long number, int local)
 			slot += hidx & _PTEIDX_GROUP_IX;
 			hptep = htab_address + slot;
 			want_v = hpte_encode_avpn(vpn, psize, ssize);
+			hpte_v = hpte_get_old_v(hptep);
+
+			if (!HPTE_V_COMPARE(hpte_v, want_v) || !(hpte_v & HPTE_V_VALID))
+				continue;
+			/* lock and try again */
 			native_lock_hpte(hptep);
 			hpte_v = hpte_get_old_v(hptep);
-			if (!HPTE_V_COMPARE(hpte_v, want_v) ||
-			    !(hpte_v & HPTE_V_VALID))
+
+			if (!HPTE_V_COMPARE(hpte_v, want_v) || !(hpte_v & HPTE_V_VALID))
 				native_unlock_hpte(hptep);
 			else
 				hptep->v = 0;
+
 		} pte_iterate_hashed_end();
 	}