linux-kernel - Re: [PATCH v1 07/14] tee: optee: add shared buffer registration functions

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Message-ID: <b0524d62-c72e-f884-cb78-9377e929dea7@epam.com>
Date:   Fri, 29 Sep 2017 18:37:00 +0300
From:   Volodymyr Babchuk <volodymyr_babchuk@...m.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        tee-dev@...ts.linaro.org,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Volodymyr Babchuk <vlad.babchuk@...il.com>
Subject: Re: [PATCH v1 07/14] tee: optee: add shared buffer registration
 functions



On 29.09.17 16:06, Mark Rutland wrote:
> On Thu, Sep 28, 2017 at 09:04:04PM +0300, Volodymyr Babchuk wrote:
>> From: Volodymyr Babchuk <vlad.babchuk@...il.com>
>>
>> This change adds ops for shm_(un)register functions in tee interface.
>> Client application can use these functions to (un)register an own shared
>> buffer in OP-TEE address space. This allows zero copy data sharing between
>> Normal and Secure Worlds.
>>
>> Please note that while those functions were added to optee code,
>> it does not report to userspace that those functions are available.
>> OP-TEE code does not set TEE_GEN_CAP_REG_MEM flag. This flag will be
>> enabled only after all other features of dynamic shared memory will be
>> implemented in subsequent patches.
> 
> While it's not adveritsed to the user, AFAICT the user could still
> invoke these via ioctls, right?

> Is there a problem if the user were to do so, or is it simply not useful
> without the other features?
Yes, user can invoke this via ioctl. And this buffer will be 
registeredin OP-TEE. But user will not be able to use this registered 
buffer, because optee driver does not know how to handle references to 
registered buffers.

This is a complex feature and I tried to split it into different commits 
to ease up review.

Probably, I can remove
+       .shm_register = optee_shm_register,
+       .shm_unregister = optee_shm_unregister,

from this patch, so user will be not able to call this functions at all. 
How do you thing? Should I do this?

> 
>> +int optee_shm_register(struct tee_context *ctx, struct tee_shm *shm,
>> +		       struct page **pages, size_t num_pages)
>> +{
> 
>> +	pages_array = optee_allocate_pages_array(num_pages);
>> +	if (!pages_array)
>> +		return -ENOMEM;
> 
>> +	msg_arg->params->u.tmem.buf_ptr = virt_to_phys(pages_array) |
>> +					  tee_shm_get_page_offset(shm);
> 
> This doesn't look right. Why is the shm page offset being orred-in to
> the pages_array physical address? They're completely separate objects.
They present the same registered shared buffer. You have a list of pages 
and offset from the first page. Strictly speaking this is not buf_ptr 
anymore, but it is named so...

This is a part of OP-TEE ABI. We considered different approaches at [1].
This fits into general ABI design.

[1] https://github.com/OP-TEE/optee_os/pull/1232#issuecomment-301851514