Re: [Xen-devel] [PATCH v4 5/6] xen: arm: relax barriers in tlb flushes

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 04/03/2014 01:18 PM, Ian Campbell wrote:
> On Thu, 2014-04-03 at 12:12 +0100, Julien Grall wrote:
>> On 04/03/2014 09:59 AM, Ian Campbell wrote:
>>> @@ -333,12 +333,12 @@ static inline void 
>>> flush_xen_data_tlb_range_va(unsigned long va,
>>>                                                 unsigned long size)
>>>  {
>>>      unsigned long end = va + size;
>>> -    dsb(sy); /* Ensure preceding are visible */
>>> +    dsb(ish); /* Ensure preceding are visible */
>>
>> I'm a bit lost with ish/nsh/sy/... shall we keep sy here?
>> flush_xen_data_tlb is used in iounmap
> 
> Is it? I can't see it. I do see it in clear_fixmap though.

Sorry I though it was used by create_xen_entries... that made me think,
create_xen_entries should use flush_xen_data_tlb_range_va as the mapping
is common with the other CPUs.

>> and we want to make sure that
>> every write as been done just before.
> 
> The barrier here is to ensure that any writes to the page tables
> themselves are complete, not really to ensure that writes using those
> page tables are complete.
> 
> If users of this call have additional requirements to make sure other
> writes complete (which iounmap surely does) then I think they need to
> have their own barriers (or further punt this up to their callers).

Right, after looking to the code, write_pte has a dsb.

-- 
Julien Grall

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