powerpc/mm/hash: Fix the reference bit update when handling hash fault

[karo-tx-linux.git] / arch / powerpc / mm / hash_utils_64.c

diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index 59268969a0bc7b0d02e8c10b28f5b214f6209006..b2740c67e1729628045dcc41fe50ecada6bac3ae 100644 (file)
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -159,6 +159,19 @@ static struct mmu_psize_def mmu_psize_defaults_gp[] = {
        },
 };
 
+/*
+ * 'R' and 'C' update notes:
+ *  - Under pHyp or KVM, the updatepp path will not set C, thus it *will*
+ *     create writeable HPTEs without C set, because the hcall H_PROTECT
+ *     that we use in that case will not update C
+ *  - The above is however not a problem, because we also don't do that
+ *     fancy "no flush" variant of eviction and we use H_REMOVE which will
+ *     do the right thing and thus we don't have the race I described earlier
+ *
+ *    - Under bare metal,  we do have the race, so we need R and C set
+ *    - We make sure R is always set and never lost
+ *    - C is _PAGE_DIRTY, and *should* always be set for a writeable mapping
+ */
 unsigned long htab_convert_pte_flags(unsigned long pteflags)
 {
        unsigned long rflags = 0;
@@ -186,9 +199,14 @@ unsigned long htab_convert_pte_flags(unsigned long pteflags)
                        rflags |= 0x1;
        }
        /*
-        * Always add "C" bit for perf. Memory coherence is always enabled
+        * We can't allow hardware to update hpte bits. Hence always
+        * set 'R' bit and set 'C' if it is a write fault
+        * Memory coherence is always enabled
         */
-       rflags |=  HPTE_R_C | HPTE_R_M;
+       rflags |=  HPTE_R_R | HPTE_R_M;
+
+       if (pteflags & _PAGE_DIRTY)
+               rflags |= HPTE_R_C;
        /*
         * Add in WIG bits
         */