Paul Mackerras <pau...@ozlabs.org> writes:
> On Tue, Feb 23, 2016 at 10:18:05AM +0530, Aneesh Kumar K.V wrote:
>> The difference between 64K and 4K hash fault handling is confusing
>> with respect to when we set _PAGE_HASHPTE in the linux pte.
>> I was trying to find out whether we miss a hpte flush in any
>> scenario because of this. ie, a pte update on a linux pte, for which we
>> are doing a parallel hash pte insert. After looking at it closer my
>> understanding is this won't happen because pte update also look at
>> _PAGE_BUSY and we will wait for hash pte insert to finish before going
>> ahead with the pte update. But to avoid further confusion keep the
>> hash fault handler for all the page size similar to __hash_page_4k.
>>
>> This partially reverts commit 41743a4e34f0 ("powerpc: Free a PTE bit on
>> ppc64 with 64K pages"
>
> In each of the functions you are modifying below, there is already an
> explicit setting of _PAGE_HASHPTE in new_pte. So I don't think this
> is necessary, or if we do this, we can eliminate the separate setting
> of _PAGE_HASHPTE later on.
>
> In general I think it's better to leave the setting of _PAGE_HASHPTE
> until we know what slot the HPTE is going to go into. That way we
> have less chance of ending up with _PAGE_HASHPTE set but bogus
> information in _PAGE_F_GIX and _PAGE_F_SECOND.
>
Ok. I will do a variant that remove _PAGE_HASHPTE setting from 4k. ie,
diff --git a/arch/powerpc/mm/hash64_4k.c b/arch/powerpc/mm/hash64_4k.c
index e3e76b929f33..47d1b26effc6 100644
--- a/arch/powerpc/mm/hash64_4k.c
+++ b/arch/powerpc/mm/hash64_4k.c
@@ -44,7 +44,7 @@ int __hash_page_4K(unsigned long ea, unsigned long access,
unsigned long vsid,
* a write access. Since this is 4K insert of 64K page size
* also add _PAGE_COMBO
*/
- new_pte = old_pte | _PAGE_BUSY | _PAGE_ACCESSED | _PAGE_HASHPTE;
+ new_pte = old_pte | _PAGE_BUSY | _PAGE_ACCESSED;
if (access & _PAGE_RW)
new_pte |= _PAGE_DIRTY;
} while (old_pte != __cmpxchg_u64((unsigned long *)ptep,
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