Merge tag 'for-6.6-rc7-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave...

[platform/kernel/linux-rpi.git] / kernel / dma / swiotlb.c

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 394494a..0163767 100644 (file)
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -399,14 +399,13 @@ void __init swiotlb_init_remap(bool addressing_limit, unsigned int flags,
        }
 
        mem->areas = memblock_alloc(array_size(sizeof(struct io_tlb_area),
-               default_nareas), SMP_CACHE_BYTES);
+               nareas), SMP_CACHE_BYTES);
        if (!mem->areas) {
                pr_warn("%s: Failed to allocate mem->areas.\n", __func__);
                return;
        }
 
-       swiotlb_init_io_tlb_pool(mem, __pa(tlb), nslabs, false,
-                                default_nareas);
+       swiotlb_init_io_tlb_pool(mem, __pa(tlb), nslabs, false, nareas);
        add_mem_pool(&io_tlb_default_mem, mem);
 
        if (flags & SWIOTLB_VERBOSE)
@@ -729,9 +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();
 }
 
 /**
@@ -1152,9 +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;