linux-kernel - [PATCH] swiotlb: iommu/dma: Move trace_swiotlb_bounced() into swiotlb_tbl_map

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Message-ID: <20250611100103.7b3c28c8@batman.local.home>
Date: Wed, 11 Jun 2025 10:01:03 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: LKML <linux-kernel@...r.kernel.org>, Linux trace kernel
 <linux-trace-kernel@...r.kernel.org>, iommu@...ts.linux.dev
Cc: Christoph Hellwig <hch@...radead.org>, Robin Murphy
 <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>, Will Deacon
 <will@...nel.org>
Subject: [PATCH] swiotlb: iommu/dma: Move trace_swiotlb_bounced() into
 swiotlb_tbl_map_single()

From: Steven Rostedt <rostedt@...dmis.org>

I'm working on code that will warn when a tracepoint is defined but not
used. As the TRACE_EVENT() logic still creates all the code regardless if
something calls the trace_<event>() function. It wastes around 5K per trace
event (less for tracepoints).

But it seems that the code in drivers/iommu/dma-iommu.c does the opposite.
It calls the trace_swiotlb_bounced() tracepoint without it being defined.
The tracepoint is defined in kernel/dma/swiotlb.c when CONFIG_SWIOTLB is
defined, but this code exists when that config is not defined.

This now fails with my work because I have all the callers reference the
tracepoint that they will call.

Thanks to the kernel test robot, it found this:

  https://lore.kernel.org/all/202506091015.7zd87kI7-lkp@intel.com/

Instead of calling trace_swiotlb_bounced() from drivers/iommu/dma-iommu.c
where it is useless when CONFIG_SWIOTLB is not defined, move the
tracepoint into swiotlb_tbl_map_single(). This also makes it consistent
with which memory is being traced (physical as supposed to dma address).

Fixes: ed18a46262be4 ("iommu/dma: Factor out a iommu_dma_map_swiotlb helper")
Closes: https://lore.kernel.org/all/20250610202457.5a599336@gandalf.local.home/
Suggested-by: Christoph Hellwig <hch@...radead.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 drivers/iommu/dma-iommu.c | 2 --
 kernel/dma/swiotlb.c      | 2 ++
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index ea2ef53bd4fe..1935b360cc94 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -1153,8 +1153,6 @@ static phys_addr_t iommu_dma_map_swiotlb(struct device *dev, phys_addr_t phys,
 		return (phys_addr_t)DMA_MAPPING_ERROR;
 	}

-	trace_swiotlb_bounced(dev, phys, size);
-
 	phys = swiotlb_tbl_map_single(dev, phys, size, iova_mask(iovad), dir,
 			attrs);

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index abcf3fa63a56..c112f1d98861 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -1379,6 +1379,8 @@ phys_addr_t swiotlb_tbl_map_single(struct device *dev, phys_addr_t orig_addr,
 	phys_addr_t tlb_addr;
 	unsigned short pad_slots;

+	trace_swiotlb_bounced(dev, orig_addr, mapping_size);
+
 	if (!mem || !mem->nslabs) {
 		dev_warn_ratelimited(dev,
 			"Can not allocate SWIOTLB buffer earlier and can't now provide you with the DMA bounce buffer");
-- 
2.47.2