[PATCH v7 20/22] dma: swiotlb: free dynamic pools from process context
From: "Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org>
Date: 2026-07-01 05:53:32
Also in:
linux-arm-kernel, linux-coco, linux-iommu, linux-s390, lkml
Subsystem:
dma mapping helpers, the rest · Maintainers:
Marek Szyprowski, Linus Torvalds
swiotlb_dyn_free() is used after removing a dynamic swiotlb pool from RCU-protected lists. It can call swiotlb_free_tlb(), which may need to restore the encryption state of an unencrypted pool with set_memory_encrypted() before freeing the pages. RCU callbacks run in atomic context, but set_memory_encrypted() is not guaranteed to be atomic-safe on all architectures. For example, page attribute updates may allocate page tables or take sleeping locks. Use queue_rcu_work() for dynamic pool freeing instead. This keeps the RCU grace period before freeing a published pool, while running the actual pool teardown from workqueue context. Use the same helper for the transient-pool error path, since that path may also be reached from atomic DMA mapping context. Tested-by: Michael Kelley <redacted> Tested-by: Mostafa Saleh <smostafa@google.com> Reviewed-by: Petr Tesarik <redacted> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org> --- include/linux/swiotlb.h | 4 ++-- kernel/dma/swiotlb.c | 19 +++++++++++-------- 2 files changed, 13 insertions(+), 10 deletions(-)
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index ee42f7588847..c3bf7ed6f7a6 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h@@ -64,7 +64,7 @@ extern void __init swiotlb_update_mem_attributes(void); * @areas: Array of memory area descriptors. * @slots: Array of slot descriptors. * @node: Member of the IO TLB memory pool list. - * @rcu: RCU head for swiotlb_dyn_free(). + * @dyn_free: RCU work item used to free the pool from process context. * @transient: %true if transient memory pool. * @cc_shared: %true if the pool memory is shared for confidential computing. */
@@ -80,7 +80,7 @@ struct io_tlb_pool { struct io_tlb_slot *slots; #ifdef CONFIG_SWIOTLB_DYNAMIC struct list_head node; - struct rcu_head rcu; + struct rcu_work dyn_free; bool transient; bool cc_shared; #endif
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index b5960c2e98d8..4d0f2c04d891 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c@@ -779,13 +779,10 @@ static void swiotlb_dyn_alloc(struct work_struct *work) add_mem_pool(mem, pool); } -/** - * swiotlb_dyn_free() - RCU callback to free a memory pool - * @rcu: RCU head in the corresponding struct io_tlb_pool. - */ -static void swiotlb_dyn_free(struct rcu_head *rcu) +static void swiotlb_dyn_free_work(struct work_struct *work) { - struct io_tlb_pool *pool = container_of(rcu, struct io_tlb_pool, rcu); + struct io_tlb_pool *pool = + container_of(to_rcu_work(work), struct io_tlb_pool, dyn_free); size_t slots_size = array_size(sizeof(*pool->slots), pool->nslabs); size_t tlb_size = pool->end - pool->start;
@@ -794,6 +791,12 @@ static void swiotlb_dyn_free(struct rcu_head *rcu) kfree(pool); } +static void swiotlb_schedule_dyn_free(struct io_tlb_pool *pool) +{ + INIT_RCU_WORK(&pool->dyn_free, swiotlb_dyn_free_work); + queue_rcu_work(system_wq, &pool->dyn_free); +} + /** * __swiotlb_find_pool() - find the IO TLB pool for a physical address * @dev: Device which has mapped the DMA buffer.
@@ -840,7 +843,7 @@ static void swiotlb_del_pool(struct device *dev, struct io_tlb_pool *pool) list_del_rcu(&pool->node); spin_unlock_irqrestore(&dev->dma_io_tlb_lock, flags); - call_rcu(&pool->rcu, swiotlb_dyn_free); + swiotlb_schedule_dyn_free(pool); } #endif /* CONFIG_SWIOTLB_DYNAMIC */
@@ -1281,7 +1284,7 @@ static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr, index = swiotlb_search_pool_area(dev, pool, 0, orig_addr, tbl_dma_addr, alloc_size, alloc_align_mask); if (index < 0) { - swiotlb_dyn_free(&pool->rcu); + swiotlb_schedule_dyn_free(pool); return -1; }
--
2.43.0