swiotlb: Reinstate page-alignment for mappings >= PAGE_SIZE

For swiotlb allocations >= PAGE_SIZE, the slab search historically
adjusted the stride to avoid checking unaligned slots. This had the
side-effect of aligning large mapping requests to PAGE_SIZE, but that
was broken by 0eee5ae10256 ("swiotlb: fix slot alignment checks").

Since this alignment could be relied upon drivers, reinstate PAGE_SIZE
alignment for swiotlb mappings >= PAGE_SIZE.

Reported-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Will Deacon <will@kernel.org>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Petr Tesarik <petr.tesarik1@huawei-partners.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index f212943e51ca5f93eb554c263d5ed2fa98bd45f7..86fe172b5958232ee29d481bf2f9fe60a51c5881 100644 (file)
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -1014,6 +1014,17 @@ static int swiotlb_search_pool_area(struct device *dev, struct io_tlb_pool *pool
        BUG_ON(!nslots);
        BUG_ON(area_index >= pool->nareas);
 
+       /*
+        * Historically, swiotlb allocations >= PAGE_SIZE were guaranteed to be
+        * page-aligned in the absence of any other alignment requirements.
+        * 'alloc_align_mask' was later introduced to specify the alignment
+        * explicitly, however this is passed as zero for streaming mappings
+        * and so we preserve the old behaviour there in case any drivers are
+        * relying on it.
+        */
+       if (!alloc_align_mask && !iotlb_align_mask && alloc_size >= PAGE_SIZE)
+               alloc_align_mask = PAGE_SIZE - 1;
+
        /*
         * Ensure that the allocation is at least slot-aligned and update
         * 'iotlb_align_mask' to ignore bits that will be preserved when
@@ -1028,13 +1039,6 @@ static int swiotlb_search_pool_area(struct device *dev, struct io_tlb_pool *pool
         */
        stride = get_max_slots(max(alloc_align_mask, iotlb_align_mask));
 
-       /*
-        * For allocations of PAGE_SIZE or larger only look for page aligned
-        * allocations.
-        */
-       if (alloc_size >= PAGE_SIZE)
-               stride = umax(stride, PAGE_SHIFT - IO_TLB_SHIFT + 1);
-
        spin_lock_irqsave(&area->lock, flags);
        if (unlikely(nslots > pool->area_nslabs - area->used))
                goto not_found;