swiotlb: allocate a new memory pool when existing pools are full

When swiotlb_find_slots() cannot find suitable slots, schedule the
allocation of a new memory pool. It is not possible to allocate the pool
immediately, because this code may run in interrupt context, which is not
suitable for large memory allocations. This means that the memory pool will
be available too late for the currently requested mapping, but the stress
on the software IO TLB allocator is likely to continue, and subsequent
allocations will benefit from the additional pool eventually.

Keep all memory pools for an allocator in an RCU list to avoid locking on
the read side. For modifications, add a new spinlock to struct io_tlb_mem.

The spinlock also protects updates to the total number of slabs (nslabs in
struct io_tlb_mem), but not reads of the value. Readers may therefore
encounter a stale value, but this is not an issue:

- swiotlb_tbl_map_single() and is_swiotlb_active() only check for non-zero
  value. This is ensured by the existence of the default memory pool,
  allocated at boot.

- The exact value is used only for non-critical purposes (debugfs, kernel
  messages).

Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 9825fa14abe4..8371c92a0271 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -8,6 +8,7 @@
 #include <linux/types.h>
 #include <linux/limits.h>
 #include <linux/spinlock.h>
+#include <linux/workqueue.h>
 
 struct device;
 struct page;
@@ -104,12 +105,16 @@ struct io_tlb_pool {
 /**
  * struct io_tlb_mem - Software IO TLB allocator
  * @defpool:	Default (initial) IO TLB memory pool descriptor.
+ * @pool:	IO TLB memory pool descriptor (if not dynamic).
  * @nslabs:	Total number of IO TLB slabs in all pools.
  * @debugfs:	The dentry to debugfs.
  * @force_bounce: %true if swiotlb bouncing is forced
  * @for_alloc:  %true if the pool is used for memory allocation
  * @can_grow:	%true if more pools can be allocated dynamically.
  * @phys_limit:	Maximum allowed physical address.
+ * @lock:	Lock to synchronize changes to the list.
+ * @pools:	List of IO TLB memory pool descriptors (if dynamic).
+ * @dyn_alloc:	Dynamic IO TLB pool allocation work.
  * @total_used:	The total number of slots in the pool that are currently used
  *		across all areas. Used only for calculating used_hiwater in
  *		debugfs.
@@ -125,6 +130,9 @@ struct io_tlb_mem {
 #ifdef CONFIG_SWIOTLB_DYNAMIC
 	bool can_grow;
 	u64 phys_limit;
+	spinlock_t lock;
+	struct list_head pools;
+	struct work_struct dyn_alloc;
 #endif
 #ifdef CONFIG_DEBUG_FS
 	atomic_long_t total_used;