On Wed, 17 May 2023 at 13:38, Christoph Hellwig hch@infradead.org wrote:
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.
Do you mean a pinned user-space page can be paged out automatically? The documentation [1] isn't very helpful here either since it talks about "short term" vs "long term" in abstract terms.
Just FYI, the underlying use-case for TEE registered shared memory is that the references to pinned pages are provided to TEE implementation to operate upon. This can happen over multiple syscalls and we want the pinned pages to be always in RAM as otherwise the physical addresses may change if they are paged out in between. If this is only supported reliably with a long term flag then this patch should be tagged as a fix and requires stable backports.
[1] Documentation/core-api/pin_user_pages.rst
-Sumit