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

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Date:   Wed, 17 May 2023 01:08:42 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Sumit Garg <sumit.garg@...aro.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        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, May 17, 2023 at 01:22:51PM +0530, Sumit Garg wrote:
> > > +#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.

long term is defined as won't automatically go away during the same
syscall.