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dma: swiotlb: free dynamic pools from process context

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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 <mhklinux@outlook.com>
Tested-by: Mostafa Saleh <smostafa@google.com>
Reviewed-by: Petr Tesarik <ptesarik@suse.com>
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
Link: https://lore.kernel.org/r/20260717180442.110954-22-aneesh.kumar@kernel.org
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
This commit is contained in:
Aneesh Kumar K.V (Arm) 2026-07-17 23:34:39 +05:30 committed by Marek Szyprowski
parent 63e62b63e8
commit e13d4d9a49
2 changed files with 13 additions and 10 deletions
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4
include/linux/swiotlb.h
View File

@ -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

19
kernel/dma/swiotlb.c
View File

@ -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;
}