diff options
Diffstat (limited to 'arch/powerpc/mm/hash_utils_64.c')
| -rw-r--r-- | arch/powerpc/mm/hash_utils_64.c | 22 |
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 7635b1c6b..f4acba25f 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; @@ -180,9 +193,14 @@ 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 */ |