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

On Wed, 17 May 2023 at 13:04, Christoph Hellwig hch@infradead.org wrote:

...

• u32 page_flag = FOLL_WRITE;
  
  if (!tee_device_get(teedev))
          return ERR_PTR(-EINVAL);
  

@@ -255,9 +256,11 @@ register_shm_helper(struct tee_context *ctx, unsigned long addr, ret = ERR_PTR(-ENOMEM); goto err_free_shm; }

+#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.

The ifdef does not make sense.

Agree.

-Sumit