Re: [PATCH v4 6/8] tee: Support kernel shm registration without dma-buf backing

Tyler Hicks
2021-06-11T13:10:04Z

On 2021-06-11 10:46:20, Sumit Garg wrote:
> On Fri, 11 Jun 2021 at 02:39, Tyler Hicks <tyhicks@linux.microsoft.com> wrote:
> >
> > Uncouple the registration of kernel shared memory buffers from the
> > TEE_SHM_DMA_BUF flag. Drivers may wish to allocate multi-page contiguous
> > shared memory regions but do not need them to be backed by a dma-buf
> > when the memory region is only used by the driver.
> >
> > If the TEE implementation does not require 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.
> >
>
> That's the main point that no other TEE implementation would honour
> TEE_SHM_REGISTER and I think it's just the incorrect usage of
> TEE_SHM_REGISTER flag to suffice OP-TEE underlying implementation.
>
> > Allow callers of tee_shm_alloc_kernel_buf() to allocate and register a
> > shared memory region without the backing of dma-buf.
> >
> > Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com>
> > ---
> > drivers/tee/optee/shm_pool.c | 5 ++---
> > drivers/tee/tee_shm.c | 13 +++++++++++--
> > 2 files changed, 13 insertions(+), 5 deletions(-)
> >
>
> This patch is just mixing two separate approaches to TEE shared
> memory. Have a look at alternative suggestions below.
>
> > 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) {
>
> Here you can just do following check instead:
>
> if (!(shm->flags & TEE_SHM_PRIV)) {

This is a bug fix series that's intended to fix the current and older
kernels. tee_shm_alloc_anon_kernel_buf()/TEE_SHM_PRIV is not present in
older kernels and isn't required to fix these kexec/kdump bugs. Your
suggestion feels like something that should be done in the allocator
rewrite that Jens is working on to clean all of this up going forward.

Tyler

>
> And this flag needs to be passed from the call sites here [1] [2].
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/tee/optee/core.c#n280
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/tee/optee/call.c#n186
>
> > 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;
>
> This should remain as it is.
>
> > 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)
>
> Same as above.
>
> > 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 c65e44707cd6..26a76f817c57 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))) {
>
> No need for this change.
>
> > 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;
> > + }
> > +
>
> This change isn't required as well as underlying TEE implementation:
> OP-TEE in this case knows how to implement shared memory allocation
> whether to use reserved shared memory pool or dynamic shared memory
> pool. For more details see shared memory pool creation in
> optee_probe().
>
> > shm->flags = flags | TEE_SHM_POOL;
> > shm->ctx = ctx;
> > if (flags & TEE_SHM_DMA_BUF)
> > @@ -207,7 +216,7 @@ EXPORT_SYMBOL_GPL(tee_shm_alloc);
> > */
> > struct tee_shm *tee_shm_alloc_kernel_buf(struct tee_context *ctx, size_t size)
> > {
> > - return tee_shm_alloc(ctx, size, TEE_SHM_MAPPED | TEE_SHM_DMA_BUF);
> > + return tee_shm_alloc(ctx, size, TEE_SHM_MAPPED | TEE_SHM_REGISTER);
>
> Here it could just be:
>
> return tee_shm_alloc(ctx, size, TEE_SHM_MAPPED);
>
> -Sumit
>
> > }
> > EXPORT_SYMBOL_GPL(tee_shm_alloc_kernel_buf);
> >
> > --
> > 2.25.1
> >
>