Subject: [PATCH v3 6/6] ARM: mm: Change the order of TLB/cache maintenance operations.

From: [email-masked] (Santosh Shilimkar)
Date: Wed, 9 Oct 2013 14:56:10 -0400

Will,

Will,

On Friday 04 October 2013 12:03 PM, Santosh Shilimkar wrote:
> On Friday 04 October 2013 11:52 AM, Will Deacon wrote:
>> On Thu, Oct 03, 2013 at 10:18:00PM +0100, Santosh Shilimkar wrote:
>>> From: Sricharan R <[email-masked]>
>>>
>>> As per the arm ARMv7 manual, the sequence of TLB maintenance
>>> operations after making changes to the translation table is
>>> to clean the dcache first, then invalidate the TLB. With
>>> the current sequence we see cache corruption when the
>>> flush_cache_all is called after tlb_flush_all.
>>>
>>> STR rx, [Translation table entry]
>>> ; write new entry to the translation table
>>> Clean cache line [Translation table entry]
>>> DSB
>>> ; ensures visibility of the data cleaned from the D Cache
>>> Invalidate TLB entry by MVA (and ASID if non-global) [page address]
>>> Invalidate BTC
>>> DSB
>>> ; ensure completion of the Invalidate TLB operation
>>> ISB
>>> ; ensure table changes visible to instruction fetch
>>>
>>> The issue is seen only with LPAE + THUMB BUILT KERNEL + 64BIT patching,
>>> which is little bit weird.
>>
>> NAK.
>>
>> I don't buy your reasoning. All current LPAE implementations also implement
>> the multi-processing extensions, meaning that the cache flush isn't required
>> to make the PTEs visible to the table walker. The dsb from the TLB_WB flag
>> is sufficient, so I think you still have some debugging to do as this change
>> is likely masking a problem elsewhere.
>>
>> On top of that, create_mapping does all the flushing you need (for the !SMP
>> case) when the tables are initialised, so this code doesn't need changing.
>>
> Fair enough. We will drop this patch from this series and continue to look
> at the issue further. As such the patch has no hard dependency with rest of
> the series.
> 
Just to update the thread, Sricharan tracked down this issue now and
the 64 bit patch is fixed.

Thanks for NAK ;)

Regards,
Santosh