Subject: [PATCH v2 2/3] powerpc/pseries: Don't fail hash page table insert for bolted mapping

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Thu, 24 Oct 2019 15:05:41 +0530

If the hypervisor returned H_PTEG_FULL for H_ENTER hcall, retry a hash page table
insert by removing a random entry from the group.

After some runtime, it is very well possible to find all the 8 hash page table
entry slot in the hpte group used for mapping. Don't fail a bolted entry insert
in that case. With Storage class memory a user can find this error easily since
a namespace enable/disable is equivalent to memory add/remove.

This results in failures as reported below:

$ ndctl create-namespace -r region1 -t pmem -m devdax -a 65536 -s 100M
libndctl: ndctl_dax_enable: dax1.3: failed to enable
  Error: namespace1.2: failed to enable

failed to create namespace: No such device or address

In kernel log we find the details as below:

Unable to create mapping for hot added memory 0xc000042006000000..0xc00004200d000000: -1
dax_pmem: probe of dax1.3 failed with error -14

This indicates that we failed to create a bolted hash table entry for direct-map
address backing the namespace.

We also observe failures such that not all namespaces will be enabled with
ndctl enable-namespace all command.

Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
Changes from v1:
* update commit message

 arch/powerpc/mm/book3s64/hash_utils.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
index 6c123760164e..6e5a769ebcb8 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -294,7 +294,14 @@ int htab_bolt_mapping(unsigned long vstart, unsigned long vend,
 		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 */
+			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 < 0)
 			break;
 
-- 
2.21.0