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-rw-r--r--arch/powerpc/mm/hash_utils_64.c22
1 files changed, 20 insertions, 2 deletions
diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index 59268969a0bc..b2740c67e172 100644
--- 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
*/