Re: [PATCH -V9 07/21] swap: Support PMD swap mapping when splitting huge PMD

["Huang\, Ying" <ying.huang@intel.com>]

Hi, Daniel,

Daniel Jordan <daniel.m.jordan@oracle.com> writes:

> +Aneesh
>
> On Fri, Dec 14, 2018 at 02:27:40PM +0800, Huang Ying wrote:
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index bd2543e10938..49df3e7c96c7 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>
>> +int split_swap_cluster_map(swp_entry_t entry)
>         ...
>> +	VM_BUG_ON(!IS_ALIGNED(offset, SWAPFILE_CLUSTER));
>
> Hi Ying, I crashed on this in v6 as reported and it still dies on me now.

Sorry, I missed the original report for v6.  I should have been more careful.

>> @@ -2150,6 +2185,9 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
>         ...
>> +	if (IS_ENABLED(CONFIG_THP_SWAP) && is_swap_pmd(old_pmd))
>> +		return __split_huge_swap_pmd(vma, haddr, pmd);
>
> Problem is 'pmd' is passed here, which has been pmdp_invalidate()ed under the
> assumption that it is not a swap entry.  pmd's pfn bits get inverted for L1TF,
> so the swap entry gets corrupted and this BUG is the first place that notices.
>
> I don't see a reason to invalidate so soon, so what about just moving the
> invalidation down, past the migration/swap checks?

Yes.  That can fix the issue.  I will fix this in that way.

Best Regards,
Huang, Ying