On Fri, 16 Dec 2022 at 10:39, Sumit Garg sumit.garg@linaro.org wrote:
On Fri, 16 Dec 2022 at 06:11, Ira Weiny ira.weiny@intel.com wrote:
On Fri, Oct 07, 2022 at 10:12:57AM +0200, Jens Wiklander wrote:
On Thu, Oct 6, 2022 at 8:20 PM Linus Torvalds torvalds@linux-foundation.org wrote:
On Wed, Oct 5, 2022 at 11:24 PM Sumit Garg sumit.garg@linaro.org wrote:
Sorry but you need to get your driver mainline in order to support vmalloc interface.
Actually, I think even then we shouldn't support vmalloc - and register_shm_helper() just needs to be changed to pass in an array of actual page pointers instead.
register_shm_helper() is an internal function, I suppose it's what's passed to tee_shm_register_user_buf() and especially tee_shm_register_kernel_buf() in this case.
So the gain is that in the kernel it becomes the caller's responsibility to provide the array of page pointers and the TEE subsystem doesn't need to care about what kind of kernel memory it is any longer. Yes, that should avoid eventual complexities with vmalloc() etc.
I finally spent some time digging into this again.
Overall I'm not opposed to trying to clean up the code more but I feel like the removal of TEE_SHM_USER_MAPPED is too complex for the main goal; to remove a caller of kmap_to_page().
Not only is that flag used in release_registered_pages() but it is also used in tee_shm_fop_mmap(). I'm not following exactly why. I think this is to allow mmap of the tee_shm's allocated by kernel users?
No, its rather to allow mmap of tee_shm allocated via tee_shm_alloc_user_buf(). Have a look at its user-space usage here [1]. So overall I agree here that we can't get rid of TEE_SHM_USER_MAPPED completely as it has a valid mmap use-case.
[1] https://github.com/OP-TEE/optee_client/blob/master/libteec/src/tee_client_ap...
Which I _think_ is orthogonal to the callers of tee_shm_register_kernel_buf()?
At that point TEE_SHM_USER_MAPPED should also go away, because then it's the caller that should just do either the user space page pinning, or pass in the kernel page pointer.
JensW, is there some reason that wouldn't work?
We still need to know if it's kernel or user pages in release_registered_pages().
Yes.
As I dug into this it seemed ok to define a tee_shm_kernel_free(). Pull out the allocation of the page array from register_shm_helper() such that it could be handled by tee_shm_register_kernel_buf() and this new tee_shm_kernel_free().
+1
This seems reasonable because the only callers of tee_shm_register_kernel_buf() are in trusted_tee.c and they all call tee_shm_free() on the registered memory prior to returning.
Other callers[*] of tee_shm_free() obtained tee_shm from tee_shm_alloc_kernel_buf() which AFAICT avoids all this nonsense.
[*] such as .../drivers/firmware/broadcom/tee_bnxt_fw.c.
The struct tee_shm:s acquired with syscalls from user space are reference counted. As are the kernel tee_shm:s, but I believe we could separate them to avoid reference counting tee_shm:s used by kernel clients if needed. I'll need to look closer at this if we're going to use that approach.
Without reference counting the caller of tee_shm_free() can be certain that the secure world is done with the memory so we could delegate the kernel pages part of release_registered_pages() to the caller instead.
I'm not sure I follow you here. Would this be along the lines of creating a tee_shm_free_kernel() to be used in trusted_tee.c for those specific kernel data?
I can't find a reason/use-case for the TEE subsystem to keep a refcount of memory registered by other kernel drivers like trusted_tee.c. So yes I think it should be safe to directly free that shm via tee_shm_free_kernel(). Also with that we can simplify shm registration by kernel clients via directly passing page pointers to tee_shm_register_kernel_buf() (I would rather rename this API as tee_shm_register_kernel_pages()).
Okay, so I will take up this work and get rid of kmap_to_page invocation from the TEE subsystem.
Ira,
You can then rebase your patchset over my work.
-Sumit
Overall I feel like submitting this series again with Christoph and Al's comments addressed is the best way forward to get rid of kmap_to_page(). I would really like to get moving on that to avoid any further issues with the kmap conversions.
But if folks feel strongly enough about removing that flag I can certainly try to do so.
Ira
Cheers, Jens
Linus