On Tue, 06 Jul 2021 08:25:26 +0100,
Sumit Garg [off-list ref] wrote:

On Thu, 17 Jun 2021 at 11:40, Jens Wiklander [off-list ref] wrote:

quoted

Hi Sumit,

On Thu, Jun 17, 2021 at 6:33 AM Sumit Garg [off-list ref] wrote:

quoted

Hi Jens,

On Wed, 16 Jun 2021 at 16:07, Jens Wiklander [off-list ref] wrote:

quoted

Hi all,

This adds support for asynchronous notifications from OP-TEE in secure
world to the OP-TEE driver. This allows a design with a top half and bottom
half type of driver where the top half runs in secure interrupt context and
a notifications tells normal world to schedule a yielding call to do the
bottom half processing.

An interrupt is used to notify the driver that there are asynchronous
notifications pending.

It looks like a nice feature. I would like to get hands on with this.
Can I test this feature on Qemu?

Absolutely, you can get this into the normal OP-TEE development repo setup with:
repo init -u https://github.com/OP-TEE/manifest.git -m default.xml
repo sync
Update optee_os with
https://github.com/jenswi-linaro/optee_os/tree/async_notif_v2
Update linux with https://github.com/jenswi-linaro/linux-1/tree/async_notif_v2
cd build
make all -j...
make run-only

If you type anything at the secure console you'll notice how it
changes behaviour once the Linux kernel has booted.

Thanks for sharing instructions as I now got some time to test and
deep dive into this feature. It looks like a pretty useful feature to
realize interrupt support in the secure world in its true sense. This
feature works for me as per your instructions.

I could recognise it's requirement from the time while I was playing
with secure timer interrupt support for OP-TEE RNG driver on
Developerbox. In that case I had to strip down the secure interrupt
handler to a minimum that would just collect entropy and dump into the
secure buffer. But with asynchronous notifications support, I could
add more functionality like entropy health tests in the bottom half
instead of doing those health tests while retrieving entropy from the
secure world.

Given that, have you explored the possibility to leverage SGI rather
than a platform specific SPI for notifying the normal world? If it's
possible to leverage Architecture specific SGI for this purpose then I

What does "Architecture specific SGI" mean?

think this feature will come automatically enabled for every platform
without the need to reserve a platform specific SPI.

That old chestnut again...

- How do you discover that the secure side has graced you with a
  Group-1 SGI (no, you can't use one of the first 8)? for both DT and
  ACPI?

- How do you find which CPUs are targeted by this SGI? All? One? A
  subset? What is the expected behaviour with CPU hotplug? How can the
  NS side (Linux) can inform the secure side about the CPUs it wants
  to use?

- Is there any case where you would instead need a level interrupt
  (which a SGI cannot provide)?

In general, cross world SGIs are a really bad idea. Yes, some people
like them. I still think they are misguided, and I don't intend to
provide a generic request interface for this.

	M.

-- 
Without deviation from the norm, progress is not possible.

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