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Re: [Xen-devel] [PATCH 1/5] xen/arm: optee: impose limit on shared buffer size

  • To: Julien Grall <julien.grall@xxxxxxx>
  • From: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
  • Date: Thu, 12 Sep 2019 19:45:37 +0000
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  • Cc: "tee-dev@xxxxxxxxxxxxxxxx" <tee-dev@xxxxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
  • Delivery-date: Thu, 12 Sep 2019 19:45:48 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Thread-index: AQHVWeNlCY0CqDi7zE2giEuaPhvOCqckA0sAgALr+QCAAZ6qAIAAA5eA
  • Thread-topic: [PATCH 1/5] xen/arm: optee: impose limit on shared buffer size

Hi Julien,

Julien Grall writes:

> Hi Volodymyr,
> On 9/11/19 7:48 PM, Volodymyr Babchuk wrote:
>> Julien Grall writes:
>>> Hi Volodymyr,
>>> On 8/23/19 7:48 PM, Volodymyr Babchuk wrote:
>>>> We want to limit number of calls to lookup_and_pin_guest_ram_addr()
>>>> per one request. There are two ways to do this: either preempt
>>>> translate_noncontig() or to limit size of one shared buffer size.
>>>> It is quite hard to preempt translate_noncontig(), because it is deep
>>>> nested. So we chose second option. We will allow 512 pages per one
>>>> shared buffer. This does not interfere with GP standard, as it
>>>> requires that size limit for shared buffer should be at lest 512kB.
>>> Do you mean "least" instead of "lest"?
>> Yes
>>> If so, why 512 pages (i.e 1MB)
>>> is plenty enough for most of the use cases? What does "xtest" consist
>>> on?
>> Bigger buffer xtest tries to allocate is mere 32KB. I believe that 1MB
>> is enough for the most cases, because OP-TEE itself have a very limited
>> resources. But this value is chosen arbitrary.
> Could we potentially reduce to let say 512KB (or maybe lower) if xtest
> only allocate 32KB?
Potentially - yes. But only to 512KB if we want to be compatible with
the Global Platform specification. Why are you asking, though?

Volodymyr Babchuk at EPAM
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