powerpc/mm: Add some debug output when hash insertion fails

This adds some debug output to our MMU hash code to print out some
useful debug data if the hypervisor refuses the insertion (which
should normally never happen).

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---

2 files changed, 31 insertions, 5 deletions

diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index 40847a9dd6db..09dffe6efa46 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -871,6 +871,18 @@ static inline int subpage_protection(struct mm_struct *mm, unsigned long ea)
 }
 #endif
 
+void hash_failure_debug(unsigned long ea, unsigned long access,
+                        unsigned long vsid, unsigned long trap,
+                        int ssize, int psize, unsigned long pte)
+{
+        if (!printk_ratelimit())
+                return;
+        pr_info("mm: Hashing failure ! EA=0x%lx access=0x%lx current=%s\n",
+                ea, access, current->comm);
+        pr_info("    trap=0x%lx vsid=0x%lx ssize=%d psize=%d pte=0x%lx\n",
+                trap, vsid, ssize, psize, pte);
+}
+
 /* Result code is:
  *  0 - handled
  *  1 - normal page fault
@@ -1036,6 +1048,12 @@ int hash_page(unsigned long ea, unsigned long access, unsigned long trap)
                                             local, ssize, spp);
         }
 
+        /* Dump some info in case of hash insertion failure, they should
+         * never happen so it is really useful to know if/when they do
+         */
+        if (rc == -1)
+                hash_failure_debug(ea, access, vsid, trap, ssize, psize,
+                                   pte_val(*ptep));
 #ifndef CONFIG_PPC_64K_PAGES
         DBG_LOW(" o-pte: %016lx\n", pte_val(*ptep));
 #else
@@ -1054,8 +1072,7 @@ void hash_preload(struct mm_struct *mm, unsigned long ea,
         void *pgdir;
         pte_t *ptep;
         unsigned long flags;
-        int local = 0;
-        int ssize;
+        int rc, ssize, local = 0;
 
         BUG_ON(REGION_ID(ea) != USER_REGION_ID);
 
@@ -1101,11 +1118,18 @@ void hash_preload(struct mm_struct *mm, unsigned long ea,
         /* Hash it in */
 #ifdef CONFIG_PPC_HAS_HASH_64K
         if (mm->context.user_psize == MMU_PAGE_64K)
-                __hash_page_64K(ea, access, vsid, ptep, trap, local, ssize);
+                rc = __hash_page_64K(ea, access, vsid, ptep, trap, local, ssize);
         else
 #endif /* CONFIG_PPC_HAS_HASH_64K */
-                __hash_page_4K(ea, access, vsid, ptep, trap, local, ssize,
-                               subpage_protection(pgdir, ea));
+                rc = __hash_page_4K(ea, access, vsid, ptep, trap, local, ssize,
+                                    subpage_protection(pgdir, ea));
+
+        /* Dump some info in case of hash insertion failure, they should
+         * never happen so it is really useful to know if/when they do
+         */
+        if (rc == -1)
+                hash_failure_debug(ea, access, vsid, trap, ssize,
+                                   mm->context.user_psize, pte_val(*ptep));
 
         local_irq_restore(flags);
 }
diff --git a/arch/powerpc/mm/hugetlbpage-hash64.c b/arch/powerpc/mm/hugetlbpage-hash64.c
index faae9ec4cb04..cc5c273086cf 100644
--- a/arch/powerpc/mm/hugetlbpage-hash64.c
+++ b/arch/powerpc/mm/hugetlbpage-hash64.c
@@ -127,6 +127,8 @@ repeat:
                  */
                 if (unlikely(slot == -2)) {
                         *ptep = __pte(old_pte);
+                        hash_failure_debug(ea, access, vsid, trap, ssize,
+                                           mmu_psize, old_pte);
                         return -1;
                 }