linux-kernel - Re: [PATCH] tee: add FOLL_LONGTERM for CMA case when alloc shm

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Date:   Wed, 17 May 2023 13:22:51 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Xiaoming Ding <xiaoming.ding@...iatek.com>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        op-tee@...ts.trustedfirmware.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, fei.xu@...iatek.com,
        srv_heupstream@...iatek.com, linux-mm@...ck.org
Subject: Re: [PATCH] tee: add FOLL_LONGTERM for CMA case when alloc shm

On Wed, 17 May 2023 at 13:04, Christoph Hellwig <hch@...radead.org> wrote:
>
> > +     u32 page_flag = FOLL_WRITE;
> >
> >       if (!tee_device_get(teedev))
> >               return ERR_PTR(-EINVAL);
> > @@ -255,9 +256,11 @@ register_shm_helper(struct tee_context *ctx, unsigned long addr,
> >               ret = ERR_PTR(-ENOMEM);
> >               goto err_free_shm;
> >       }
> > -
> > +#if IS_ENABLED(CONFIG_CMA)
> > +     page_flag |= FOLL_LONGTERM;
> > +#endif
> >       if (flags & TEE_SHM_USER_MAPPED)
>
> If this mapping is long live it should always use FOLL_LONGTERM.

It depends on the userspace application needs. However, I think it
should be safe to use FOLL_LONGTERM by default to serve cases like
secure media playback.

>
> The ifdef does not make sense.

Agree.

-Sumit