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From:   Sumit Garg <sumit.garg@linaro.org>
Date:   Wed, 17 May 2023 13:22:51 +0530
Message-ID: <CAFA6WYO+AvnbuAdWyBAQ8HkLaOno7PXdsPb9SubxrGNvAm4UnQ@mail.gmail.com>
Subject: Re: [PATCH] tee: add FOLL_LONGTERM for CMA case when alloc shm
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Xiaoming Ding <xiaoming.ding@mediatek.com>,
        Jens Wiklander <jens.wiklander@linaro.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        op-tee@lists.trustedfirmware.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, fei.xu@mediatek.com,
        srv_heupstream@mediatek.com, linux-mm@kvack.org
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On Wed, 17 May 2023 at 13:04, Christoph Hellwig <hch@infradead.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