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-rw-r--r--include/linux/swiotlb.h23
-rw-r--r--kernel/dma/swiotlb.c26
2 files changed, 36 insertions, 13 deletions
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index b4536626f8ff..ecde0312dd52 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -172,14 +172,23 @@ static inline bool is_swiotlb_buffer(struct device *dev, phys_addr_t paddr)
if (!mem)
return false;
- if (IS_ENABLED(CONFIG_SWIOTLB_DYNAMIC)) {
- /* Pairs with smp_wmb() in swiotlb_find_slots() and
- * swiotlb_dyn_alloc(), which modify the RCU lists.
- */
- smp_rmb();
- return swiotlb_find_pool(dev, paddr);
- }
+#ifdef CONFIG_SWIOTLB_DYNAMIC
+ /*
+ * All SWIOTLB buffer addresses must have been returned by
+ * swiotlb_tbl_map_single() and passed to a device driver.
+ * If a SWIOTLB address is checked on another CPU, then it was
+ * presumably loaded by the device driver from an unspecified private
+ * data structure. Make sure that this load is ordered before reading
+ * dev->dma_uses_io_tlb here and mem->pools in swiotlb_find_pool().
+ *
+ * This barrier pairs with smp_mb() in swiotlb_find_slots().
+ */
+ smp_rmb();
+ return READ_ONCE(dev->dma_uses_io_tlb) &&
+ swiotlb_find_pool(dev, paddr);
+#else
return paddr >= mem->defpool.start && paddr < mem->defpool.end;
+#endif
}
static inline bool is_swiotlb_force_bounce(struct device *dev)
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 85dd94323b98..01637677736f 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -728,9 +728,6 @@ static void swiotlb_dyn_alloc(struct work_struct *work)
}
add_mem_pool(mem, pool);
-
- /* Pairs with smp_rmb() in is_swiotlb_buffer(). */
- smp_wmb();
}
/**
@@ -1151,9 +1148,26 @@ static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr,
spin_unlock_irqrestore(&dev->dma_io_tlb_lock, flags);
found:
- dev->dma_uses_io_tlb = true;
- /* Pairs with smp_rmb() in is_swiotlb_buffer() */
- smp_wmb();
+ WRITE_ONCE(dev->dma_uses_io_tlb, true);
+
+ /*
+ * The general barrier orders reads and writes against a presumed store
+ * of the SWIOTLB buffer address by a device driver (to a driver private
+ * data structure). It serves two purposes.
+ *
+ * First, the store to dev->dma_uses_io_tlb must be ordered before the
+ * presumed store. This guarantees that the returned buffer address
+ * cannot be passed to another CPU before updating dev->dma_uses_io_tlb.
+ *
+ * Second, the load from mem->pools must be ordered before the same
+ * presumed store. This guarantees that the returned buffer address
+ * cannot be observed by another CPU before an update of the RCU list
+ * that was made by swiotlb_dyn_alloc() on a third CPU (cf. multicopy
+ * atomicity).
+ *
+ * See also the comment in is_swiotlb_buffer().
+ */
+ smp_mb();
*retpool = pool;
return index;