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

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Message-ID: <20250502114043.1968976-2-john.ernberg@actia.se>
Date: Fri, 2 May 2025 11:40:55 +0000
From: John Ernberg <john.ernberg@...ia.se>
To: Juergen Gross <jgross@...e.com>, Stefano Stabellini
	<sstabellini@...nel.org>
CC: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>, Catalin Marinas
	<catalin.marinas@....com>, Andrew Morton <akpm@...ux-foundation.org>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>, John Ernberg
	<john.ernberg@...ia.se>, "stable@...nel.org" <stable@...nel.org>
Subject: [PATCH 1/2] xen: swiotlb: Use swiotlb bouncing if kmalloc allocation
 demands it

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@actia.se/
Fixes: 4ab5f8ec7d71 ("mm/slab: decouple ARCH_KMALLOC_MINALIGN from ARCH_DMA_MINALIGN")
Cc: stable@...nel.org # v6.5+
Signed-off-by: John Ernberg <john.ernberg@...ia.se>

---

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