Re: [Xen-devel] [PATCH v2 09/13] optee: add support for arbitrary shared memory

[Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>]

Hi Julien,

On 11.09.18 16:37, Julien Grall wrote:
> Hi Volodymyr,
>
> On 10/09/18 19:04, Volodymyr Babchuk wrote:
> > On 10.09.18 17:02, Julien Grall wrote:
> > > On 03/09/18 17:54, Volodymyr Babchuk wrote:
[...]
> > > > +    if ( !pages_data_xen_start )
> > > > +        return false;
> > > > +
> > > > +    shm_buf = allocate_shm_buf(ctx, param->u.tmem.shm_ref, num_pages);
> > > In alocate_shm_buf you are now globally limiting the number of pages 
> > > ( (16384) to pin. However, this does not limit per call.
> > > With the current limit, you would could call up to 16384 times 
> > > lookup_and_pin_guest_ram_addr(...). On Arm, for p2m related 
> > > operation, we limit to 512 iterations in one go before checking the 
> > > preemption.
> > > So I think 16384 times is far too much.
> > So, in other words, I can translate only 2MB buffer (if 4096KB pages 
> > are used), is it right?
> 2MB for the whole command. So if you have 5 buffer in the command, then 
> the sum of the buffer should not be bigger than 2MB.
4  buffers, but yes, it can be up to 8MB. Okay, I'll add per-call 
counter to limit memory usage for a whole call.
> However, 2MB might be too big considering that you also need to account 
> the SMC call. Does buffer can be passed for fast call?
No, all such calls are yielding calls, so you can ignore time used for 
SMC call itself.

--
Volodymyr Babchuk

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