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

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Date: Thu, 13 Jun 2024 23:10:57 +0530
From: Bibek Kumar Patro <quic_bibekkum@...cinc.com>
To: Greg KH <greg@...ah.com>
CC: "Isaac J. Manjarres" <isaacmanjarres@...gle.com>, <stable@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>, Will Deacon
	<will@...nel.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>, Tom Murphy
	<murphyt7@....ie>,
        Saravana Kannan <saravanak@...gle.com>,
        Joerg Roedel
	<jroedel@...e.de>, <kernel-team@...roid.com>,
        <iommu@...ts.linux-foundation.org>, <iommu@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5.15.y] iommu/dma: Trace bounce buffer usage when mapping
 buffers



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@...r.kernel.org # v5.15+
>>> Cc: Tom Murphy <murphyt7@....ie>
>>> Cc: Lu Baolu <baolu.lu@...ux.intel.com>
>>> Cc: Saravana Kannan <saravanak@...gle.com>
>>> Signed-off-by: Isaac J. Manjarres <isaacmanjarres@...gle.com>
>>> Link: https://lore.kernel.org/r/20231208234141.2356157-1-isaacmanjarres@google.com
>>> Signed-off-by: Joerg Roedel <jroedel@...e.de>
>>> (cherry picked from commit a63c357b9fd56ad5fe64616f5b22835252c6a76a)
>>> Signed-off-by: Isaac J. Manjarres <isaacmanjarres@...gle.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 ?

Thanks & regards,
Bibek

> thanks
> 
> greg k-h