[PATCH v2] tee: shm: fix slab page refcounting

[Marco Felsch]

Hi Sumit,

On 26-02-13, Sumit Garg wrote:
> Hi Marco,
> 
> On Thu, Feb 12, 2026 at 01:58:30PM +0100, Marco Felsch wrote:
> > Hi Sumit,
> > 
> > TBH: I was hoping that you will take care of this since you're marked as
> > maintainer for the tee-trusted-key and we noticed the warning with 6.14
> > and still no fix available :/
> 
> Mathew did suggested a fix long back on which everybody agreed but

You agreed. I said that the current TEE API also allows non-slabed based
backed memory and therefore I don't wanted to send this patch approach
and instead asked you to do so since you're the maintainer and fine with
the change.

> didn't got enough attention from you to test and report if that fixed

Why should it get attention from us? Maybe we do have different views of
being a maintainer.

> your issue. Since you insisted further, I have created a formal fix

Why is it our issue? It's everyones issue which uses the tee trusted-key
driver.

> patch based on that here [1]. Care to test that?

A colleague of mine is going to test it and will reply on the patch.

> [1] https://lore.kernel.org/all/20260213113317.1728769-1-sumit.garg@kernel.org/

...

> > I checked the code once again and figured that we could drop/replace
> > tee_shm_register_kernel_buf() with tee_shm_alloc_kernel_buf(). I don't
> > see why a kernel driver needs to tee_shm_register_kernel_buf() in the
> > first place, maybe this is legacy. The only users of
> > tee_shm_register_kernel_buf() are trusted_tee.c and tee_stmm_efi.c.
> 
> No it's not legacy but allows for efficient memory reuse within the
> kernel as to not create bounce buffers to share data with TEE.

To be hones, there are only two driver using the API. The tee_stmm_efi
driver can do the alloc during the probe(). The trusted_tee has to use a
bounce buffer, yes but how often do you assume that (un)sealing and rng
ops have to be done during runtime? This shouldn't be a overhead at all.

Therefore my suggestion would be still to drop the internal kernel API
and only use it for userspace pages, where it could really matter.

Regards,
  Marco
-- 
#gernperDu 
#CallMeByMyFirstName

Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | https://www.pengutronix.de/ |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-9    |