[PATCH 1/2] xen: swiotlb: Use swiotlb bouncing if kmalloc allocation demands it

[John Ernberg]

Xen swiotlb support was missed when the patch set starting with
4ab5f8ec7d71 ("mm/slab: decouple ARCH_KMALLOC_MINALIGN from
ARCH_DMA_MINALIGN") was merged.

When running Xen on iMX8QXP, a SoC without IOMMU, the effect was that USB
transfers ended up corrupted when there was more than one URB inflight at
the same time.

Add a call to dma_kmalloc_needs_bounce() to make sure that allocations too
small for DMA get bounced via swiotlb.

Closes: https://lore.kernel.org/linux-usb/ab2776f0-b838-4cf6-a12a-c208eb6aad59@xxxxxxxx/
Fixes: 4ab5f8ec7d71 ("mm/slab: decouple ARCH_KMALLOC_MINALIGN from ARCH_DMA_MINALIGN")
Cc: stable@xxxxxxxxxx # v6.5+
Signed-off-by: John Ernberg <john.ernberg@xxxxxxxx>

---

It's impossible to pick an exact fixes tag since this driver was missed
in the flagged patch set. I picked one I felt gave a decent enough picture
for someone coming across this later.
---
 drivers/xen/swiotlb-xen.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 1f65795cf5d7..ef56a2500ed6 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -217,6 +217,7 @@ static dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page,
 	 * buffering it.
 	 */
 	if (dma_capable(dev, dev_addr, size, true) &&
+	    !dma_kmalloc_needs_bounce(dev, size, dir) &&
 	    !range_straddles_page_boundary(phys, size) &&
 		!xen_arch_need_swiotlb(dev, phys, dev_addr) &&
 		!is_swiotlb_force_bounce(dev))
-- 
2.49.0