Re: [PATCH v3 5/7] tee: Support shm registration without dma-buf backing

Sumit Garg
2021-06-09T04:29:36Z

Hi Tyler,

On Wed, 9 Jun 2021 at 05:55, Tyler Hicks <tyhicks@linux.microsoft.com> wrote:
>
> Uncouple the registration of dynamic shared memory buffers from the
> TEE_SHM_DMA_BUF flag. Drivers may wish to allocate dynamic shared memory
> regions but do not need them to be backed by a dma-buf when the memory
> region is private to the driver.

In this case drivers should use tee_shm_register() instead where the
memory allocated is actually private to the driver. However, you need
to remove TEE_SHM_DMA_BUF as a mandatory flag for tee_shm_register().
Have a look at an example here [1]. So modifying tee_shm_alloc() for
this purpose doesn't look appropriate to me.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/security/keys/trusted-keys/trusted_tee.c#n73

-Sumit

>
> Allow callers of tee_shm_alloc() to specify the TEE_SHM_REGISTER flag to
> request registration. If the TEE implementation does not require dynamic
> shared memory to be registered, clear the flag prior to calling the
> corresponding pool alloc function. Update the OP-TEE driver to respect
> TEE_SHM_REGISTER, rather than TEE_SHM_DMA_BUF, when deciding whether to
> (un)register on alloc/free operations. The AMD-TEE driver continues to
> ignore the TEE_SHM_REGISTER flag.
>
> Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com>
> ---
> drivers/tee/optee/shm_pool.c | 5 ++---
> drivers/tee/tee_shm.c | 11 ++++++++++-
> 2 files changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/tee/optee/shm_pool.c b/drivers/tee/optee/shm_pool.c
> index da06ce9b9313..6054343a29fb 100644
> --- a/drivers/tee/optee/shm_pool.c
> +++ b/drivers/tee/optee/shm_pool.c
> @@ -27,7 +27,7 @@ static int pool_op_alloc(struct tee_shm_pool_mgr *poolm,
> shm->paddr = page_to_phys(page);
> shm->size = PAGE_SIZE << order;
>
> - if (shm->flags & TEE_SHM_DMA_BUF) {
> + if (shm->flags & TEE_SHM_REGISTER) {
> unsigned int nr_pages = 1 << order, i;
> struct page **pages;
>
> @@ -42,7 +42,6 @@ static int pool_op_alloc(struct tee_shm_pool_mgr *poolm,
> page++;
> }
>
> - shm->flags |= TEE_SHM_REGISTER;
> rc = optee_shm_register(shm->ctx, shm, pages, nr_pages,
> (unsigned long)shm->kaddr);
> kfree(pages);
> @@ -60,7 +59,7 @@ static int pool_op_alloc(struct tee_shm_pool_mgr *poolm,
> static void pool_op_free(struct tee_shm_pool_mgr *poolm,
> struct tee_shm *shm)
> {
> - if (shm->flags & TEE_SHM_DMA_BUF)
> + if (shm->flags & TEE_SHM_REGISTER)
> optee_shm_unregister(shm->ctx, shm);
>
> free_pages((unsigned long)shm->kaddr, get_order(shm->size));
> diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
> index 00472f5ce22e..1c0176550b9c 100644
> --- a/drivers/tee/tee_shm.c
> +++ b/drivers/tee/tee_shm.c
> @@ -117,7 +117,7 @@ struct tee_shm *tee_shm_alloc(struct tee_context *ctx, size_t size, u32 flags)
> return ERR_PTR(-EINVAL);
> }
>
> - if ((flags & ~(TEE_SHM_MAPPED | TEE_SHM_DMA_BUF))) {
> + if ((flags & ~(TEE_SHM_MAPPED | TEE_SHM_DMA_BUF | TEE_SHM_REGISTER))) {
> dev_err(teedev->dev.parent, "invalid shm flags 0x%x", flags);
> return ERR_PTR(-EINVAL);
> }
> @@ -137,6 +137,15 @@ struct tee_shm *tee_shm_alloc(struct tee_context *ctx, size_t size, u32 flags)
> goto err_dev_put;
> }
>
> + if (!teedev->desc->ops->shm_register ||
> + !teedev->desc->ops->shm_unregister) {
> + /* registration is not required by the TEE implementation */
> + flags &= ~TEE_SHM_REGISTER;
> + } else if (flags & TEE_SHM_DMA_BUF) {
> + /* all dma-buf backed shm allocations are registered */
> + flags |= TEE_SHM_REGISTER;
> + }
> +
> shm->flags = flags | TEE_SHM_POOL;
> shm->ctx = ctx;
> if (flags & TEE_SHM_DMA_BUF)
> --
> 2.25.1
>