powerpc/mm: Check for matching hpte without taking hpte lock
With smaller hash page table config, we would end up in situation
where we would be replacing hash page table slot frequently. In
such config, we will find the hpte to be not matching, and we
can do that check without holding the hpte lock. We need to
recheck the hpte again after holding lock.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/mm/hash_native_64.c b/arch/powerpc/mm/hash_native_64.c
index d53288a..558e50b 100644
--- a/arch/powerpc/mm/hash_native_64.c
+++ b/arch/powerpc/mm/hash_native_64.c
@@ -294,8 +294,6 @@
DBG_LOW(" update(vpn=%016lx, avpnv=%016lx, group=%lx, newpp=%lx)",
vpn, want_v & HPTE_V_AVPN, slot, newpp);
- native_lock_hpte(hptep);
-
hpte_v = be64_to_cpu(hptep->v);
/*
* We need to invalidate the TLB always because hpte_remove doesn't do
@@ -308,16 +306,24 @@
DBG_LOW(" -> miss\n");
ret = -1;
} else {
- DBG_LOW(" -> hit\n");
- /* Update the HPTE */
- hptep->r = cpu_to_be64((be64_to_cpu(hptep->r) & ~(HPTE_R_PP | HPTE_R_N)) |
- (newpp & (HPTE_R_PP | HPTE_R_N | HPTE_R_C)));
+ native_lock_hpte(hptep);
+ /* recheck with locks held */
+ hpte_v = be64_to_cpu(hptep->v);
+ if (unlikely(!HPTE_V_COMPARE(hpte_v, want_v) ||
+ !(hpte_v & HPTE_V_VALID))) {
+ ret = -1;
+ } else {
+ DBG_LOW(" -> hit\n");
+ /* Update the HPTE */
+ hptep->r = cpu_to_be64((be64_to_cpu(hptep->r) &
+ ~(HPTE_R_PP | HPTE_R_N)) |
+ (newpp & (HPTE_R_PP | HPTE_R_N |
+ HPTE_R_C)));
+ }
+ native_unlock_hpte(hptep);
}
- native_unlock_hpte(hptep);
-
/* Ensure it is out of the tlb too. */
tlbie(vpn, bpsize, apsize, ssize, local);
-
return ret;
}