linux-kernel - Re: [PATCH v9 00/13] firmware: qcom: qseecom: convert to using the TZ allocator

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Date: Fri, 29 Mar 2024 11:22:02 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Maximilian Luz <luzmaximilian@...il.com>
Cc: Andy Gross <agross@...nel.org>, Bjorn Andersson <andersson@...nel.org>, 
	Konrad Dybcio <konrad.dybcio@...aro.org>, Elliot Berman <quic_eberman@...cinc.com>, 
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, 
	Guru Das Srinagesh <quic_gurus@...cinc.com>, Andrew Halaney <ahalaney@...hat.com>, 
	Alex Elder <elder@...aro.org>, Srini Kandagatla <srinivas.kandagatla@...aro.org>, 
	Arnd Bergmann <arnd@...db.de>, linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, kernel@...cinc.com, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v9 00/13] firmware: qcom: qseecom: convert to using the TZ allocator

On Thu, Mar 28, 2024 at 7:55 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> On Thu, Mar 28, 2024 at 5:50 PM Maximilian Luz <luzmaximilian@...il.com> wrote:
> >
> > If I understand correctly, it enters an atomic section in
> > qcom_tzmem_alloc() and then tries to schedule somewhere down the line.
> > So this shouldn't be qseecom specific.
> >
> > I should probably also say that I'm currently testing this on a patched
> > v6.8 kernel, so there's a chance that it's my fault. However, as far as
> > I understand, it enters an atomic section in qcom_tzmem_alloc() and then
> > later tries to expand the pool memory with dma_alloc_coherent(). Which
> > AFAIK is allowed to sleep with GFP_KERNEL (and I guess that that's the
> > issue here).
> >
> > I've also tried the shmem allocator option, but that seems to get stuck
> > quite early at boot, before I even have usb-serial access to get any
> > logs. If I can find some more time, I'll try to see if I can get some
> > useful output for that.
> >
>
> Ah, I think it happens here:
>
> +       guard(spinlock_irqsave)(&pool->lock);
> +
> +again:
> +       vaddr = gen_pool_alloc(pool->genpool, size);
> +       if (!vaddr) {
> +               if (qcom_tzmem_try_grow_pool(pool, size, gfp))
> +                       goto again;
>
> We were called with GFP_KERNEL so this is what we pass on to
> qcom_tzmem_try_grow_pool() but we're now holding the spinlock. I need
> to revisit it. Thanks for the catch!
>
> Bart

Can you try the following tree?

    https://git.codelinaro.org/bartosz_golaszewski/linux.git
topic/shm-bridge-v10

gen_pool_alloc() and gen_pool_add_virt() can be used without external
serialization. We only really need to protect the list of areas in the
pool when adding a new element. We could possibly even use
list_add_tail_rcu() as it updates the pointers atomically and go
lockless.

Bart