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

[Greg KH]

On Thu, Jun 13, 2024 at 04:01:01PM +0530, Bibek Kumar Patro wrote:
> 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 */
> 
> 

Why not just take whatever change upstream fixes this instead of a
one-off change?

thanks

greg k-h