Re: [Xen-devel] [PATCH v02 1/7] arm: introduce remoteprocessor iommu module

[Andrii Tseglytskyi <andrii.tseglytskyi@xxxxxxxxxxxxxxx>]

Hi Ian

On Wed, Jul 16, 2014 at 6:34 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> On Wed, 2014-07-16 at 16:29 +0100, Ian Campbell wrote:
>> WRT the shadowing, I don't see the bit which causes the guest pages
>> which it is using as PT page for the remoteproc to get marked R/O to
>> force a trap. Perhaps that comes later.
>>
>> Do these remoteproc page tables get frequently updated at run time or
>> are they mostly just build once and forget?
>
> Reading the next patch I'm concluding that the translation happens each
> time you write to the MMU's base pointer. IOW every update requires you
> to rewrite that pointer, is that right?
>

Not exactly. Continuing an explanation from prev mail - this just an
entry point for translation. IPU and GPU work in a bit different way.

IPU is quite straight forward
Boot -> Allocate all memory -> Update register -> Xen performs translation

GPU:

Step one:
Reset -> Allocate several pages of memory -> Update register -> Xen
performas translation

Step two:
Allocate several new pagetables -> Flush caches -> call
do_translate_pagetable hypercall

Here I don't have any registers update. GPU kernel driver uses
interprocess messaging mechanism to pass physical pointers of newly
allocated pagetables directly to GPU device. So, I use hypercall which
translate pagetable during device creation.


Regards,
Andrii

> Ian.
>



-- 

Andrii Tseglytskyi | Embedded Dev
GlobalLogic
www.globallogic.com

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