From: Christoph Hellwig <hch@infradead.org>
To: David Hildenbrand <david@redhat.com>
Cc: Sumit Garg <sumit.garg@linaro.org>,
Christoph Hellwig <hch@infradead.org>,
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
Subject: FOLL_LONGTERM vs FOLL_EPHEMERAL Re: [PATCH] tee: add FOLL_LONGTERM for CMA case when alloc shm
Date: Wed, 17 May 2023 21:20:59 -0700 [thread overview]
Message-ID: <ZGWnq/dAYELyKpTy@infradead.org> (raw)
In-Reply-To: <d4773626-6cf0-c929-c775-a84ac41fd719@redhat.com>
On Wed, May 17, 2023 at 08:23:33PM +0200, David Hildenbrand wrote:
> In general: if user space controls it -> possibly forever -> long-term. Even
> if in most cases it's a short delay: there is no trusting on user space.
>
> For example, iouring fixed buffers keep pages pinned until user space
> decides to unregistered the buffers -> long-term.
>
> Short-term is, for example, something like O_DIRECT where we pin -> DMA ->
> unpin in essentially one operation.
Btw, one thing that's been on my mind is that I think we got the
polarity on FOLL_LONGTERM wrong. Instead of opting into the long term
behavior it really should be the default, with a FOLL_EPHEMERAL flag
to opt out of it. And every users of this flag is required to have
a comment explaining the life time rules for the pin..
next prev parent reply other threads:[~2023-05-18 4:21 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20230517031856.19660-1-xiaoming.ding@mediatek.com>
2023-05-17 7:34 ` Christoph Hellwig
2023-05-17 7:52 ` Sumit Garg
2023-05-17 8:08 ` Christoph Hellwig
2023-05-17 9:02 ` Xiaoming Ding (丁晓明)
2023-05-17 9:26 ` Sumit Garg
2023-05-17 9:36 ` Christoph Hellwig
2023-05-17 10:19 ` Sumit Garg
2023-05-17 18:23 ` David Hildenbrand
2023-05-18 4:20 ` Christoph Hellwig [this message]
2023-05-18 6:08 ` FOLL_LONGTERM vs FOLL_EPHEMERAL " Sumit Garg
2023-05-18 13:56 ` David Hildenbrand
2023-05-23 1:54 ` John Hubbard
2023-05-23 7:25 ` Lorenzo Stoakes
2023-06-13 5:30 ` Xiaoming Ding (丁晓明)
2023-06-13 8:48 ` Sumit Garg
2023-05-18 6:40 ` Xiaoming Ding (丁晓明)
2023-05-19 10:01 ` David Hildenbrand
2023-05-19 11:03 ` Sumit Garg
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