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Date: Fri, 14 Jun 2024 07:18:01 +0200
From: Greg KH <greg@kroah.com>
To: Bibek Kumar Patro <quic_bibekkum@quicinc.com>
Cc: "Isaac J. Manjarres" <isaacmanjarres@google.com>,
	stable@vger.kernel.org, Joerg Roedel <joro@8bytes.org>,
	Will Deacon <will@kernel.org>, Lu Baolu <baolu.lu@linux.intel.com>,
	Tom Murphy <murphyt7@tcd.ie>,
	Saravana Kannan <saravanak@google.com>,
	Joerg Roedel <jroedel@suse.de>, kernel-team@android.com,
	iommu@lists.linux-foundation.org, iommu@lists.linux.dev,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5.15.y] iommu/dma: Trace bounce buffer usage when mapping
 buffers
Message-ID: <2024061450-pueblo-recipient-d4a6@gregkh>
References: <2024012226-unmanned-marshy-5819@gregkh>
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 <ZmrKZYJ0+z3mRZXx@hu-bibekkum-hyd.qualcomm.com>
 <2024061311-washable-ranch-abc5@gregkh>
 <3c5034e9-d834-4ebe-a03d-1a222f8f22ac@quicinc.com>
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In-Reply-To: <3c5034e9-d834-4ebe-a03d-1a222f8f22ac@quicinc.com>

On Thu, Jun 13, 2024 at 11:10:57PM +0530, Bibek Kumar Patro wrote:
> 
> 
> On 6/13/2024 4:45 PM, Greg KH wrote:
> > 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@vger.kernel.org # v5.15+
> > > > Cc: Tom Murphy <murphyt7@tcd.ie>
> > > > Cc: Lu Baolu <baolu.lu@linux.intel.com>
> > > > Cc: Saravana Kannan <saravanak@google.com>
> > > > Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
> > > > Link: https://lore.kernel.org/r/20231208234141.2356157-1-isaacmanjarres@google.com
> > > > Signed-off-by: Joerg Roedel <jroedel@suse.de>
> > > > (cherry picked from commit a63c357b9fd56ad5fe64616f5b22835252c6a76a)
> > > > Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
> > > > ---
> > > >   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?
> > 
> 
> I am currently checking the history on swiotlb_force and how it's
> removed in latest kernel versions. If those changes are applicable on
> this stable branch can we explore backporting those instead of this one-
> off change ?

Please backport what is in the tree already.