On Wed, Mar 26, 2025 at 12:07 PM Marco Felsch m.felsch@pengutronix.de wrote:
On 25-03-26, Matthew Wilcox wrote:
On Tue, Mar 25, 2025 at 09:07:39PM +0100, Marco Felsch wrote:
Skip manipulating the refcount in case of slab pages according commit b9c0e49abfca ("mm: decline to manipulate the refcount on a slab page").
This almost certainly isn't right. I know nothing about TEE, but that you are doing this indicates a problem. The hack that we put into networking should not be blindly replicated.
Why are you taking a reference on the pages to begin with? Is it copy and pasted from somewhere else, or was there actual thought put into it?
Not sure, this belongs to the TEE maintainers.
I don't know. We were getting the user pages first, so I assume we just did the same thing when we added support for kernel pages.
If it's "prevent the caller from freeing the allocation", well, it never accomplished that with slab allocations. So for callers that do kmalloc (eg setup_mm_hdr() in drivers/firmware/efi/stmm/tee_stmm_efi.c), you have to rely on them not freeing the allocation while the TEE driver has it.
And if that's your API contract, then there's no point in taking refcounts on other kinds of pages either; it's just unnecessary atomic instructions. So the right patch might be something like this:
+++ b/drivers/tee/tee_shm.c @@ -15,29 +15,11 @@ #include <linux/highmem.h> #include "tee_private.h"
I had the same diff but didn't went this way since we can't be sure that iov's are always slab backed. As far as I understood IOVs. In 'worst-case' scenario an iov can be backed by different page types too.
We're only using kvec's. Briefly, before commit 7bdee4157591 ("tee: Use iov_iter to better support shared buffer registration") we checked with is_vmalloc_addr() || is_kmap_addr(). I like Matthew's suggestion, it's nice to fix problems by deleting code. :-)
Sumit, you know the callers better. What do you think?
Cheers, Jens
Regards, Marco
-static void shm_put_kernel_pages(struct page **pages, size_t page_count) -{
size_t n;for (n = 0; n < page_count; n++)put_page(pages[n]);-}
-static void shm_get_kernel_pages(struct page **pages, size_t page_count) -{
size_t n;for (n = 0; n < page_count; n++)get_page(pages[n]);-}
static void release_registered_pages(struct tee_shm *shm) { if (shm->pages) { if (shm->flags & TEE_SHM_USER_MAPPED) unpin_user_pages(shm->pages, shm->num_pages);
elseshm_put_kernel_pages(shm->pages, shm->num_pages); kfree(shm->pages); }@@ -321,13 +303,6 @@ register_shm_helper(struct tee_context *ctx, struct iov_iter *iter, u32 flags, goto err_free_shm_pages; }
/** iov_iter_extract_kvec_pages does not get reference on the pages,* get a reference on them.*/if (iov_iter_is_kvec(iter))shm_get_kernel_pages(shm->pages, num_pages);shm->offset = off; shm->size = len; shm->num_pages = num_pages;@@ -341,10 +316,8 @@ register_shm_helper(struct tee_context *ctx, struct iov_iter *iter, u32 flags,
return shm;err_put_shm_pages:
if (!iov_iter_is_kvec(iter))
if (iter_is_uvec(iter)) unpin_user_pages(shm->pages, shm->num_pages);
elseshm_put_kernel_pages(shm->pages, shm->num_pages);err_free_shm_pages: kfree(shm->pages); err_free_shm: