linux-kernel - Re: [PATCH v3 5/7] tee: Support shm registration without dma-buf backing

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Date:   Thu, 10 Jun 2021 16:05:01 -0500
From:   Tyler Hicks <tyhicks@...ux.microsoft.com>
To:     Jens Wiklander <jens.wiklander@...aro.org>
Cc:     Sumit Garg <sumit.garg@...aro.org>, Rijo-john.Thomas@....com,
        Allen Pais <apais@...ux.microsoft.com>,
        Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Vikas Gupta <vikas.gupta@...adcom.com>,
        Thirupathaiah Annapureddy <thiruan@...rosoft.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Rafał Miłecki <zajec5@...il.com>,
        op-tee@...ts.trustedfirmware.org,
        linux-integrity <linux-integrity@...r.kernel.org>,
        bcm-kernel-feedback-list@...adcom.com, linux-mips@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 5/7] tee: Support shm registration without dma-buf
 backing

On 2021-06-10 09:49:48, Jens Wiklander wrote:
> On Wed, Jun 09, 2021 at 08:42:25AM -0500, Tyler Hicks wrote:
> [snip]
> > > I've just posted "[PATCH 0/7] tee: shared memory updates",
> > > https://lore.kernel.org/lkml/20210609102324.2222332-1-jens.wiklander@linaro.org/
> > > 
> > > Where tee_shm_alloc() is replaced by among other functions
> > > tee_shm_alloc_kernel_buf(). tee_shm_alloc_kernel_buf() takes care of the
> > > problem with TEE_SHM_DMA_BUF.
> > 
> > Thanks! At first glance, that series would take care of the last three
> > patches in my kexec/kdump series.
> > 
> > I'm a bit worried that it is a rewrite of the shm allocator. Do you plan
> > to send all of that to stable? (I mentioned earlier in this thread that
> > I'm affected by these bugs in linux-5.4.y.)
> 
> No, that might be a bit much.
> 
> > Also, you and Sumit don't seem to have the same opinion on kernel
> > drivers making use of tee_shm_register() for allocations that are only
> > used internally. Can you comment on that?
> > 
> > I'm not clear on the next steps for fixing these kexec/kdump bugs in
> > older releases. I appreciate any guidance here.
> 
> Neither am I be honest. You're the only one that has brought up this
> problem so perhaps it's enough to focus on the stable branch you need to
> have fixed.

I've already added Fixes tags to all of my patches. If you are
comfortable with them going to stable, you'd add
'Cc: stable@...r.kernel.org' to them if/when you merge them so that the
stable team will ensure that they're applied.

Note that I'm not the only person that brought up this bug:

 https://github.com/OP-TEE/optee_os/issues/3637

Once I started digging in, I realized that there were more kexec/kdump
bugs and the series grew.

> If I've understood it correctly it's best if it's possible to
> cherry-pick the fixes from mainline to the stable branch in question.
> So we must make sure to get your needed patches in before any rewrites
> that would make cherry-picking impossible. The rewrite I'm proposing
> isn't urgent so it can be held off for a while.

Thanks for holding off. I'll be quick on my revisions so that you don't
have to moth ball your series for too much longer.

Tyler

> 
> Cheers,
> Jens
>