lkml.org 
[lkml]   [2023]   [May]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectFOLL_LONGTERM vs FOLL_EPHEMERAL Re: [PATCH] tee: add FOLL_LONGTERM for CMA case when alloc shm
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..

\
 
 \ /
  Last update: 2023-05-18 06:21    [W:0.892 / U:0.136 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site