Re: [PATCH v8 9/9] sparc64: Add support for ADI (Application Data Integrity)

[Khalid Aziz <khalid.aziz@oracle.com>]

On 10/12/2017 02:27 PM, Anthony Yznaga wrote:
> 
>> On Oct 12, 2017, at 7:44 AM, Khalid Aziz <khalid.aziz@oracle.com> wrote:
>>
>>
>> On 10/06/2017 04:12 PM, Anthony Yznaga wrote:
>>>> On Sep 25, 2017, at 9:49 AM, Khalid Aziz <khalid.aziz@oracle.com> wrote:
>>>>
>>>> This patch extends mprotect to enable ADI (TSTATE.mcde), enable/disable
>>>> MCD (Memory Corruption Detection) on selected memory ranges, enable
>>>> TTE.mcd in PTEs, return ADI parameters to userspace and save/restore ADI
>>>> version tags on page swap out/in or migration. ADI is not enabled by
>>> I still don't believe migration is properly supported.  Your
>>> implementation is relying on a fault happening on a page while its
>>> migration is in progress so that do_swap_page() will be called, but
>>> I don't see how do_swap_page() will be called if a fault does not
>>> happen until after the migration has completed.
>>
>> User pages are on LRU list and for the mapped pages on LRU list, migrate_pages() ultimately calls try_to_unmap_one and makes a migration swap entry for the page being migrated. This forces a page fault upon access on the destination node and the page is swapped back in from swap cache. The fault is forced by the migration swap entry, rather than fault being an accidental event. If page fault happens on the destination node while migration is in progress, do_swap_page() waits until migration is done. Please take a look at the code in __unmap_and_move().
> 
> I looked at the code again, and I now believe ADI tags are never restored for migrated pages.  Here's why:
> 

I will take a look at it again. I have run extensive tests migrating 
pages of a process across multiple NUMA nodes over and over again and 
ADI tags were never lost, so this does work. I won't rule out the 
possibility of having missed a code path where tags are not restored and 
I will look for it.

Thanks,
Khalid

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