Subject: [PATCH 3/3] powerpc/book3s64/hash: Use secondary hash for bolted mapping if the primary is full

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Sat, 28 Sep 2019 20:23:32 +0530

With bolted hash page table entry, kernel currently only use primary hash group
when inserting the hash page table entry. In the rare case where we find all the
8 primary hash slot occupied by bolted entries, this can result in hash page
table insert failure for bolted entries. Avoid this by using the secondary hash
group.
This is different from what kernel does the non-bolted mapping. With non-bolted
we try secondary before removing an existing entry from hash page table group.
With bolted we prefer primary hash group and hence try to insert the page table
entry by removing a slot from primary before trying the secondary hash group.

Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
 arch/powerpc/mm/book3s64/hash_native.c | 38 ++++++++++++++++++++------
 arch/powerpc/mm/book3s64/hash_utils.c  | 13 ++++++++-
 arch/powerpc/platforms/pseries/lpar.c  | 14 ++++++++--
 3 files changed, 52 insertions(+), 13 deletions(-)

diff --git a/arch/powerpc/mm/book3s64/hash_native.c b/arch/powerpc/mm/book3s64/hash_native.c
index 90ab4f31e2b3..f1d979cc662a 100644
--- a/arch/powerpc/mm/book3s64/hash_native.c
+++ b/arch/powerpc/mm/book3s64/hash_native.c
@@ -459,19 +459,12 @@ static long native_hpte_updatepp(unsigned long slot, unsigned long newpp,
 	return ret;
 }
 
-static long native_hpte_find(unsigned long vpn, int psize, int ssize)
+static long __native_hpte_find(unsigned long want_v, unsigned long slot)
 {
 	struct hash_pte *hptep;
-	unsigned long hash;
+	unsigned long hpte_v;
 	unsigned long i;
-	long slot;
-	unsigned long want_v, hpte_v;
 
-	hash = hpt_hash(vpn, mmu_psize_defs[psize].shift, ssize);
-	want_v = hpte_encode_avpn(vpn, psize, ssize);
-
-	/* Bolted mappings are only ever in the primary group */
-	slot = (hash & htab_hash_mask) * HPTES_PER_GROUP;
 	for (i = 0; i < HPTES_PER_GROUP; i++) {
 
 		hptep = htab_address + slot;
@@ -485,6 +478,33 @@ static long native_hpte_find(unsigned long vpn, int psize, int ssize)
 	return -1;
 }
 
+static long native_hpte_find(unsigned long vpn, int psize, int ssize)
+{
+	unsigned long hpte_group;
+	unsigned long want_v;
+	unsigned long hash;
+	long slot;
+
+	hash = hpt_hash(vpn, mmu_psize_defs[psize].shift, ssize);
+	want_v = hpte_encode_avpn(vpn, psize, ssize);
+
+	/*
+	 * We try to keep bolted entries always in primary hash
+	 * But in some case we can find them in secondary too.
+	 */
+	hpte_group = (hash & htab_hash_mask) * HPTES_PER_GROUP;
+	slot = __native_hpte_find(want_v, hpte_group);
+	if (slot < 0) {
+		/* Try in secondary */
+		hpte_group = (~hash & htab_hash_mask) * HPTES_PER_GROUP;
+		slot = __native_hpte_find(want_v, hpte_group);
+		if (slot < 0)
+			return -1;
+	}
+
+	return slot;
+}
+
 /*
  * Update the page protection bits. Intended to be used to create
  * guard pages for kernel data structures on pages which are bolted
diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
index 9afff4fa8b07..ae38120a94e3 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -263,6 +263,7 @@ int htab_bolt_mapping(unsigned long vstart, unsigned long vend,
 		unsigned long vsid = get_kernel_vsid(vaddr, ssize);
 		unsigned long vpn  = hpt_vpn(vaddr, vsid, ssize);
 		unsigned long tprot = prot;
+		bool secondary_hash = false;
 
 		/*
 		 * If we hit a bad address return error.
@@ -291,17 +292,27 @@ int htab_bolt_mapping(unsigned long vstart, unsigned long vend,
 		hpteg = ((hash & htab_hash_mask) * HPTES_PER_GROUP);
 
 		BUG_ON(!mmu_hash_ops.hpte_insert);
+repeat:
 		ret = mmu_hash_ops.hpte_insert(hpteg, vpn, paddr, tprot,
 					       HPTE_V_BOLTED, psize, psize,
 					       ssize);
 		if (ret == -1) {
-			/* Try to remove a non bolted entry */
+			/*
+			 * Try to to keep bolted entries in primary.
+			 * Remove non bolted entries and try insert again
+			 */
 			ret = mmu_hash_ops.hpte_remove(hpteg);
 			if (ret != -1)
 				ret = mmu_hash_ops.hpte_insert(hpteg, vpn, paddr, tprot,
 							       HPTE_V_BOLTED, psize, psize,
 							       ssize);
+			if (ret == -1 && !secondary_hash) {
+				secondary_hash = true;
+				hpteg = ((~hash & htab_hash_mask) * HPTES_PER_GROUP);
+				goto repeat;
+			}
 		}
+
 		if (ret < 0)
 			break;
 
diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index fdd8933d15a2..0acb2f096dd8 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -922,11 +922,19 @@ static long pSeries_lpar_hpte_find(unsigned long vpn, int psize, int ssize)
 	hash = hpt_hash(vpn, mmu_psize_defs[psize].shift, ssize);
 	want_v = hpte_encode_avpn(vpn, psize, ssize);
 
-	/* Bolted entries are always in the primary group */
+	/*
+	 * We try to keep bolted entries always in primary hash
+	 * But in some case we can find them in secondary too.
+	 */
 	hpte_group = (hash & htab_hash_mask) * HPTES_PER_GROUP;
 	slot = __pSeries_lpar_hpte_find(want_v, hpte_group);
-	if (slot < 0)
-		return -1;
+	if (slot < 0) {
+		/* Try in secondary */
+		hpte_group = (~hash & htab_hash_mask) * HPTES_PER_GROUP;
+		slot = __pSeries_lpar_hpte_find(want_v, hpte_group);
+		if (slot < 0)
+			return -1;
+	}
 	return hpte_group + slot;
 }
 
-- 
2.21.0