Re: [PATCH 5.15.y] iommu/dma: Trace bounce buffer usage when mapping buffers

[Bibek Kumar Patro]

On Mon, Jan 22, 2024 at 12:37:54PM -0800, Isaac J. Manjarres wrote:
> When commit 82612d66d51d ("iommu: Allow the dma-iommu api to
> use bounce buffers") was introduced, it did not add the logic
> for tracing the bounce buffer usage from iommu_dma_map_page().
> 
> All of the users of swiotlb_tbl_map_single() trace their bounce
> buffer usage, except iommu_dma_map_page(). This makes it difficult
> to track SWIOTLB usage from that function. Thus, trace bounce buffer
> usage from iommu_dma_map_page().
> 
> Fixes: 82612d66d51d ("iommu: Allow the dma-iommu api to use bounce buffers")
> Cc: stable@xxxxxxxxxxxxxxx # v5.15+
> Cc: Tom Murphy <murphyt7@xxxxxx>
> Cc: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Cc: Saravana Kannan <saravanak@xxxxxxxxxx>
> Signed-off-by: Isaac J. Manjarres <isaacmanjarres@xxxxxxxxxx>
> Link: https://lore.kernel.org/r/20231208234141.2356157-1-isaacmanjarres@xxxxxxxxxx
> Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
> (cherry picked from commit a63c357b9fd56ad5fe64616f5b22835252c6a76a)
> Signed-off-by: Isaac J. Manjarres <isaacmanjarres@xxxxxxxxxx>
> ---
>  drivers/iommu/dma-iommu.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 48c6f7ff4aef..8cd63e6ccd2c 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -25,6 +25,7 @@
>  #include <linux/vmalloc.h>
>  #include <linux/crash_dump.h>
>  #include <linux/dma-direct.h>
> +#include <trace/events/swiotlb.h>
>  
>  struct iommu_dma_msi_page {
>  	struct list_head	list;
> @@ -817,6 +818,8 @@ static dma_addr_t iommu_dma_map_page(struct device *dev, struct page *page,
>  		void *padding_start;
>  		size_t padding_size, aligned_size;
>  
> +		trace_swiotlb_bounced(dev, phys, size, swiotlb_force);
> +

Hi, this backported patch trying to access swiotlb_force variable is
causing a build conflict where CONFIG_SWIOTLB is not enabled.

In file included from kernel/drivers/iommu/dma-iommu.c:28:
kernel/include/trace/events/swiotlb.h:15:9: error: declaration of 'enum SWIOTLB_NO_FORCE' will not be visible outside of this function [-Werror,-Wvisibility]
                 enum swiotlb_force swiotlb_force),
                      ^
kernel/include/linux/swiotlb.h:143:23: note: expanded from macro 'swiotlb_force'
#define swiotlb_force SWIOTLB_NO_FORCE
                      ^
In file included from kernel/drivers/iommu/dma-iommu.c:28:
kernel/include/trace/events/swiotlb.h:15:9: error: declaration of 'enum SWIOTLB_NO_FORCE' will not be visible outside of this function [-Werror,-Wvisibility]
kernel/include/linux/swiotlb.h:143:23: note: expanded from macro 'swiotlb_force'
#define swiotlb_force SWIOTLB_NO_FORCE
                      ^
In file included from kernel/drivers/iommu/dma-iommu.c:28:
kernel/include/trace/events/swiotlb.h:15:9: error: declaration of 'enum SWIOTLB_NO_FORCE' will not be visible outside of this function [-Werror,-Wvisibility]
kernel/include/linux/swiotlb.h:143:23: note: expanded from macro 'swiotlb_force'
#define swiotlb_force SWIOTLB_NO_FORCE
                      ^
In file included from kernel/drivers/iommu/dma-iommu.c:28:
kernel/include/trace/events/swiotlb.h:15:9: error: declaration of 'enum SWIOTLB_NO_FORCE' will not be visible outside of this function [-Werror,-Wvisibility]
kernel/include/linux/swiotlb.h:143:23: note: expanded from macro 'swiotlb_force'
#define swiotlb_force SWIOTLB_NO_FORCE
                      ^
kernel/drivers/iommu/dma-iommu.c:865:42: error: argument type 'enum SWIOTLB_NO_FORCE' is incomplete
                                       trace_swiotlb_bounced(dev, phys, size, swiotlb_force);
                                                                              ^~~~~~~~~~~~~
kernel/include/linux/swiotlb.h:143:23: note: expanded from macro 'swiotlb_force'
#define swiotlb_force SWIOTLB_NO_FORCE
                      ^~~~~~~~~~~~~~~~
kernel/include/trace/events/swiotlb.h:15:9: note: forward declaration of 'enum SWIOTLB_NO_FORCE'
enum swiotlb_force swiotlb_force),
     ^
kernel/include/linux/swiotlb.h:143:23: note: expanded from macro 'swiotlb_force'
#define swiotlb_force SWIOTLB_NO_FORCE

--------------------------------------------------------------------------------------------------------------------------------------------------

I have a simple proposed fix which can resolve this compile time conflict when CONFIG_SWIOTLB is disabled.

--- a/include/trace/events/swiotlb.h
+++ b/include/trace/events/swiotlb.h
@@ -7,6 +7,7 @@

 #include <linux/tracepoint.h>

+#ifdef CONFIG_SWIOTLB
 TRACE_EVENT(swiotlb_bounced,

        TP_PROTO(struct device *dev,
@@ -43,6 +44,9 @@ TRACE_EVENT(swiotlb_bounced,
                        { SWIOTLB_FORCE,        "FORCE" },
                        { SWIOTLB_NO_FORCE,     "NO_FORCE" }))
 );
+#else
+#define trace_swiotlb_bounced(dev, phys, size, swiotlb_force)
+#endif /* CONFIG_SWIOTLB */

 #endif /*  _TRACE_SWIOTLB_H */


Thanks & regards,
Bibek

>  		aligned_size = iova_align(iovad, size);
>  		phys = swiotlb_tbl_map_single(dev, phys, size, aligned_size,
>  					      iova_mask(iovad), dir, attrs);
> -- 
> 2.43.0.429.g432eaa2c6b-goog
>