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

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Date:   Wed, 17 May 2023 09:02:42 +0000
From:   Xiaoming Ding (丁晓明) 
        <Xiaoming.Ding@...iatek.com>
To:     "hch@...radead.org" <hch@...radead.org>,
        "sumit.garg@...aro.org" <sumit.garg@...aro.org>
CC:     Fei Xu (徐飞) <Fei.Xu@...iatek.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "srv_heupstream@...iatek.com" <srv_heupstream@...iatek.com>,
        "jens.wiklander@...aro.org" <jens.wiklander@...aro.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "op-tee@...ts.trustedfirmware.org" <op-tee@...ts.trustedfirmware.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH] tee: add FOLL_LONGTERM for CMA case when alloc shm

On Wed, 2023-05-17 at 01:08 -0700, Christoph Hellwig wrote:
> External email : Please do not click links or open attachments until
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> 
> 
> 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.

thanks for the suggestion.
I will update the patch with using FOLL_LONGTERM by default.