Re: [Xen-devel] [PATCH] xen: arm: invalidate caches after map_domain_page done

[Andrii Tseglytskyi <andrii.tseglytskyi@xxxxxxxxxxxxxxx>]

 Hi Julien,

On Fri, Aug 1, 2014 at 8:49 PM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
>
>
> On 01/08/14 16:06, Andrii Tseglytskyi wrote:
>>
>> Looks like I see where is the issue:
>> After mapping done kernel driver calls flush_tlb_all() function, which
>> just invalidates cache, it does the similar command, as the following
>
>
> flush_tlb_all doesn't invalidate the cache but the TLB.
>
>
>> Xen macros:
>>
>> #define DTLBIALL        p15,0,c8,c6,0   /* Invalidate data TLB */
>>
>> Then after mapping done, remoteproc_iommu starts translation, calls
>> map_domain_page() -> flush_xen_data_tlb_range_va_local(),
>> which is described with following macros:
>>
>> #define TLBIMVAH        p15,4,c8,c7,1   /* Invalidate Unified Hyp. TLB by
>> MVA */
>>
>> So, I got 2 invalidates and no cleans. And when I started using
>> clean_and_invalidate_xen_dcache_va_range() I got both:
>>
>> #define DCCIMVAC        p15,0,c7,c14,1  /* Data cache clean and
>> invalidate by MVA */
>>
>> I need both - clean and invalidate. If I don't have clean - data may
>> still present in cache and not flushed to RAM - I will see invalid
>> data after map_domain_page() call
>
>
> You seem to mix TLB and cache in your mail. If the page has been mapped with
> cache attribute (should be done by kmalloc), then it should not have any
> issue in Xen.
>
> Your patch is removing the TLB flush and you are very lucky that Xen is
> still working correctly...

I will not remove TLB flush and modify common code. In any case
map_domain_page() does not work as is for me.
And I think that having any dependencies on how page is mapped in
kernel - cacheable or not is not the best solution for me.
I think I'll introduce a new wrapper with map_domain_page() and proper
cache invalidation API, which will work for me.

Thanks a lot for detailed review and clear explanations ))

Regards,
Andrii

>
> Regards,
>
> --
> Julien Grall



-- 

Andrii Tseglytskyi | Embedded Dev
GlobalLogic
www.globallogic.com

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