Merge tag 'dma-mapping-6.3-2023-03-31' of git://git.infradead.org/users/hch/dma-mapping

Pull dma-mapping fixes from Christoph Hellwig:

 - fix for swiotlb deadlock due to wrong alignment checks (GuoRui.Yu,
   Petr Tesarik)

* tag 'dma-mapping-6.3-2023-03-31' of git://git.infradead.org/users/hch/dma-mapping:
  swiotlb: fix slot alignment checks
  swiotlb: use wrap_area_index() instead of open-coding it
  swiotlb: fix the deadlock in swiotlb_do_find_slots

Author: torvalds

kernel/dma/swiotlb.c

@@ -625,39 +625,44 @@ static int swiotlb_do_find_slots(struct device *dev, int area_index,
 	unsigned int iotlb_align_mask =
 		dma_get_min_align_mask(dev) & ~(IO_TLB_SIZE - 1);
 	unsigned int nslots = nr_slots(alloc_size), stride;
-	unsigned int index, wrap, count = 0, i;
 	unsigned int offset = swiotlb_align_offset(dev, orig_addr);
+	unsigned int index, slots_checked, count = 0, i;
 	unsigned long flags;
 	unsigned int slot_base;
 	unsigned int slot_index;
 
 	BUG_ON(!nslots);
 	BUG_ON(area_index >= mem->nareas);
 
+	/*
+	 * For allocations of PAGE_SIZE or larger only look for page aligned
+	 * allocations.
+	 */
+	if (alloc_size >= PAGE_SIZE)
+		iotlb_align_mask &= PAGE_MASK;
+	iotlb_align_mask &= alloc_align_mask;
+
 	/*
 	 * For mappings with an alignment requirement don't bother looping to
-	 * unaligned slots once we found an aligned one.  For allocations of
-	 * PAGE_SIZE or larger only look for page aligned allocations.
+	 * unaligned slots once we found an aligned one.
 	 */
 	stride = (iotlb_align_mask >> IO_TLB_SHIFT) + 1;
-	if (alloc_size >= PAGE_SIZE)
-		stride = max(stride, stride << (PAGE_SHIFT - IO_TLB_SHIFT));
-	stride = max(stride, (alloc_align_mask >> IO_TLB_SHIFT) + 1);
 
 	spin_lock_irqsave(&area->lock, flags);
 	if (unlikely(nslots > mem->area_nslabs - area->used))
 		goto not_found;
 
 	slot_base = area_index * mem->area_nslabs;
-	index = wrap = wrap_area_index(mem, ALIGN(area->index, stride));
+	index = area->index;
 
-	do {
+	for (slots_checked = 0; slots_checked < mem->area_nslabs; ) {
 		slot_index = slot_base + index;
 
 		if (orig_addr &&
 		    (slot_addr(tbl_dma_addr, slot_index) &
 		     iotlb_align_mask) != (orig_addr & iotlb_align_mask)) {
 			index = wrap_area_index(mem, index + 1);
+			slots_checked++;
 			continue;
 		}
 
@@ -673,7 +678,8 @@ static int swiotlb_do_find_slots(struct device *dev, int area_index,
 				goto found;
 		}
 		index = wrap_area_index(mem, index + stride);
-	} while (index != wrap);
+		slots_checked += stride;
+	}
 
 not_found:
 	spin_unlock_irqrestore(&area->lock, flags);
@@ -693,10 +699,7 @@ static int swiotlb_do_find_slots(struct device *dev, int area_index,
 	/*
 	 * Update the indices to avoid searching in the next round.
 	 */
-	if (index + nslots < mem->area_nslabs)
-		area->index = index + nslots;
-	else
-		area->index = 0;
+	area->index = wrap_area_index(mem, index + nslots);
 	area->used += nslots;
 	spin_unlock_irqrestore(&area->lock, flags);
 	return slot_index;