drivers/dma-buf/udmabuf.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
When CONFIG_DMA_API_DEBUG_SG is enabled, importing a udmabuf into a DRM
driver (e.g. amdgpu for video playback in GNOME Videos / Showtime)
triggers a spurious warning:
DMA-API: amdgpu 0000:03:00.0: cacheline tracking EEXIST, \
overlapping mappings aren't supported
WARNING: kernel/dma/debug.c:619 at add_dma_entry+0x473/0x5f0
The call chain is:
amdgpu_cs_ioctl
-> amdgpu_ttm_backend_bind
-> dma_buf_map_attachment
-> [udmabuf] map_udmabuf -> get_sg_table
-> dma_map_sgtable(dev, sg, direction, 0) // attrs=0
-> debug_dma_map_sg -> add_dma_entry -> EEXIST
This happens because udmabuf builds a per-page scatter-gather list via
sg_set_folio(). When begin_cpu_udmabuf() has already created an sg
table mapped for the misc device, and an importer such as amdgpu maps
the same pages for its own device via map_udmabuf(), the DMA debug
infrastructure sees two active mappings whose physical addresses share
cacheline boundaries and warns about the overlap.
The DMA_ATTR_SKIP_CPU_SYNC flag suppresses this check in
add_dma_entry() because it signals that no CPU cache maintenance is
performed at map/unmap time, making the cacheline overlap harmless.
All other major dma-buf exporters already pass this flag:
- drm_gem_map_dma_buf() passes DMA_ATTR_SKIP_CPU_SYNC
- amdgpu_dma_buf_map() passes DMA_ATTR_SKIP_CPU_SYNC
The CPU sync at map/unmap time is also redundant for udmabuf:
begin_cpu_udmabuf() and end_cpu_udmabuf() already perform explicit
cache synchronization via dma_sync_sgtable_for_cpu/device() when CPU
access is requested through the dma-buf interface.
Pass DMA_ATTR_SKIP_CPU_SYNC to dma_map_sgtable() and
dma_unmap_sgtable() in udmabuf to suppress the spurious warning and
skip the redundant sync.
Fixes: 284562e1f348 ("udmabuf: implement begin_cpu_access/end_cpu_access hooks")
Cc: stable@vger.kernel.org
Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
---
drivers/dma-buf/udmabuf.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index 94b8ecb892bb..9c6f8785a28a 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -162,7 +162,7 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
sg_set_folio(sgl, ubuf->folios[i], PAGE_SIZE,
ubuf->offsets[i]);
- ret = dma_map_sgtable(dev, sg, direction, 0);
+ ret = dma_map_sgtable(dev, sg, direction, DMA_ATTR_SKIP_CPU_SYNC);
if (ret < 0)
goto err_map;
return sg;
@@ -177,7 +177,7 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
static void put_sg_table(struct device *dev, struct sg_table *sg,
enum dma_data_direction direction)
{
- dma_unmap_sgtable(dev, sg, direction, 0);
+ dma_unmap_sgtable(dev, sg, direction, DMA_ATTR_SKIP_CPU_SYNC);
sg_free_table(sg);
kfree(sg);
}
--
2.53.0On Tue, Mar 17, 2026 at 10:37 AM Mikhail Gavrilov
<mikhail.v.gavrilov@gmail.com> wrote:
>
> When CONFIG_DMA_API_DEBUG_SG is enabled, importing a udmabuf into a DRM
> driver (e.g. amdgpu for video playback in GNOME Videos / Showtime)
> triggers a spurious warning:
>
> DMA-API: amdgpu 0000:03:00.0: cacheline tracking EEXIST, \
> overlapping mappings aren't supported
> WARNING: kernel/dma/debug.c:619 at add_dma_entry+0x473/0x5f0
>
> The call chain is:
>
> amdgpu_cs_ioctl
> -> amdgpu_ttm_backend_bind
> -> dma_buf_map_attachment
> -> [udmabuf] map_udmabuf -> get_sg_table
> -> dma_map_sgtable(dev, sg, direction, 0) // attrs=0
> -> debug_dma_map_sg -> add_dma_entry -> EEXIST
>
> This happens because udmabuf builds a per-page scatter-gather list via
> sg_set_folio(). When begin_cpu_udmabuf() has already created an sg
> table mapped for the misc device, and an importer such as amdgpu maps
> the same pages for its own device via map_udmabuf(), the DMA debug
> infrastructure sees two active mappings whose physical addresses share
> cacheline boundaries and warns about the overlap.
>
> The DMA_ATTR_SKIP_CPU_SYNC flag suppresses this check in
> add_dma_entry() because it signals that no CPU cache maintenance is
> performed at map/unmap time, making the cacheline overlap harmless.
>
> All other major dma-buf exporters already pass this flag:
> - drm_gem_map_dma_buf() passes DMA_ATTR_SKIP_CPU_SYNC
> - amdgpu_dma_buf_map() passes DMA_ATTR_SKIP_CPU_SYNC
>
> The CPU sync at map/unmap time is also redundant for udmabuf:
> begin_cpu_udmabuf() and end_cpu_udmabuf() already perform explicit
> cache synchronization via dma_sync_sgtable_for_cpu/device() when CPU
> access is requested through the dma-buf interface.
>
> Pass DMA_ATTR_SKIP_CPU_SYNC to dma_map_sgtable() and
> dma_unmap_sgtable() in udmabuf to suppress the spurious warning and
> skip the redundant sync.
>
> Fixes: 284562e1f348 ("udmabuf: implement begin_cpu_access/end_cpu_access hooks")
> Cc: stable@vger.kernel.org
> Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
> ---
> drivers/dma-buf/udmabuf.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index 94b8ecb892bb..9c6f8785a28a 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -162,7 +162,7 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
> sg_set_folio(sgl, ubuf->folios[i], PAGE_SIZE,
> ubuf->offsets[i]);
>
> - ret = dma_map_sgtable(dev, sg, direction, 0);
> + ret = dma_map_sgtable(dev, sg, direction, DMA_ATTR_SKIP_CPU_SYNC);
> if (ret < 0)
> goto err_map;
> return sg;
> @@ -177,7 +177,7 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
> static void put_sg_table(struct device *dev, struct sg_table *sg,
> enum dma_data_direction direction)
> {
> - dma_unmap_sgtable(dev, sg, direction, 0);
> + dma_unmap_sgtable(dev, sg, direction, DMA_ATTR_SKIP_CPU_SYNC);
> sg_free_table(sg);
> kfree(sg);
> }
> --
> 2.53.0
>
Gentle ping on this patch.
To summarize the review so far:
Vivek: "Looks OK to me"
Christian: Acked-by
Note: while my separate dma-debug patch [1] would also suppress
this specific warning on x86, the udmabuf fix here is still
valuable as it removes the redundant CPU sync at map/unmap time
and aligns udmabuf with other dma-buf exporters that already
pass DMA_ATTR_SKIP_CPU_SYNC.
[1] https://lore.kernel.org/all/20260327124156.24820-1-mikhail.v.gavrilov@gmail.com/
Gerd, could you take a look when you have a chance?
--
Best Regards,
Mike Gavrilov.
Hi Mikhail,
> Subject: Re: [PATCH] dma-buf/udmabuf: skip redundant cpu sync to fix
> cacheline EEXIST warning
>
> On Tue, Mar 17, 2026 at 10:37 AM Mikhail Gavrilov
> <mikhail.v.gavrilov@gmail.com> wrote:
> >
> > When CONFIG_DMA_API_DEBUG_SG is enabled, importing a udmabuf
> into a DRM
> > driver (e.g. amdgpu for video playback in GNOME Videos / Showtime)
> > triggers a spurious warning:
> >
> > DMA-API: amdgpu 0000:03:00.0: cacheline tracking EEXIST, \
> > overlapping mappings aren't supported
> > WARNING: kernel/dma/debug.c:619 at add_dma_entry+0x473/0x5f0
> >
> > The call chain is:
> >
> > amdgpu_cs_ioctl
> > -> amdgpu_ttm_backend_bind
> > -> dma_buf_map_attachment
> > -> [udmabuf] map_udmabuf -> get_sg_table
> > -> dma_map_sgtable(dev, sg, direction, 0) // attrs=0
> > -> debug_dma_map_sg -> add_dma_entry -> EEXIST
> >
> > This happens because udmabuf builds a per-page scatter-gather list
> via
> > sg_set_folio(). When begin_cpu_udmabuf() has already created an sg
> > table mapped for the misc device, and an importer such as amdgpu
> maps
> > the same pages for its own device via map_udmabuf(), the DMA
> debug
> > infrastructure sees two active mappings whose physical addresses
> share
> > cacheline boundaries and warns about the overlap.
> >
> > The DMA_ATTR_SKIP_CPU_SYNC flag suppresses this check in
> > add_dma_entry() because it signals that no CPU cache maintenance is
> > performed at map/unmap time, making the cacheline overlap
> harmless.
> >
> > All other major dma-buf exporters already pass this flag:
> > - drm_gem_map_dma_buf() passes DMA_ATTR_SKIP_CPU_SYNC
> > - amdgpu_dma_buf_map() passes DMA_ATTR_SKIP_CPU_SYNC
> >
> > The CPU sync at map/unmap time is also redundant for udmabuf:
> > begin_cpu_udmabuf() and end_cpu_udmabuf() already perform
> explicit
> > cache synchronization via dma_sync_sgtable_for_cpu/device() when
> CPU
> > access is requested through the dma-buf interface.
> >
> > Pass DMA_ATTR_SKIP_CPU_SYNC to dma_map_sgtable() and
> > dma_unmap_sgtable() in udmabuf to suppress the spurious warning
> and
> > skip the redundant sync.
> >
> > Fixes: 284562e1f348 ("udmabuf: implement
> begin_cpu_access/end_cpu_access hooks")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
> > ---
> > drivers/dma-buf/udmabuf.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> > index 94b8ecb892bb..9c6f8785a28a 100644
> > --- a/drivers/dma-buf/udmabuf.c
> > +++ b/drivers/dma-buf/udmabuf.c
> > @@ -162,7 +162,7 @@ static struct sg_table *get_sg_table(struct
> device *dev, struct dma_buf *buf,
> > sg_set_folio(sgl, ubuf->folios[i], PAGE_SIZE,
> > ubuf->offsets[i]);
> >
> > - ret = dma_map_sgtable(dev, sg, direction, 0);
> > + ret = dma_map_sgtable(dev, sg, direction,
> DMA_ATTR_SKIP_CPU_SYNC);
> > if (ret < 0)
> > goto err_map;
> > return sg;
> > @@ -177,7 +177,7 @@ static struct sg_table *get_sg_table(struct
> device *dev, struct dma_buf *buf,
> > static void put_sg_table(struct device *dev, struct sg_table *sg,
> > enum dma_data_direction direction)
> > {
> > - dma_unmap_sgtable(dev, sg, direction, 0);
> > + dma_unmap_sgtable(dev, sg, direction,
> DMA_ATTR_SKIP_CPU_SYNC);
> > sg_free_table(sg);
> > kfree(sg);
> > }
> > --
> > 2.53.0
> >
>
> Gentle ping on this patch.
>
> To summarize the review so far:
> Vivek: "Looks OK to me"
> Christian: Acked-by
>
> Note: while my separate dma-debug patch [1] would also suppress
> this specific warning on x86, the udmabuf fix here is still
> valuable as it removes the redundant CPU sync at map/unmap time
> and aligns udmabuf with other dma-buf exporters that already
> pass DMA_ATTR_SKIP_CPU_SYNC.
>
> [1] https://lore.kernel.org/all/20260327124156.24820-1-
> mikhail.v.gavrilov@gmail.com/
>
> Gerd, could you take a look when you have a chance?
I am convinced that this patch is useful in some cases, so I'll add Christian's
Ack and push it (into drm-misc-next) in a day or two.
Thanks,
Vivek
>
> --
> Best Regards,
> Mike Gavrilov.
Hi Mikhail,
> Subject: RE: [PATCH] dma-buf/udmabuf: skip redundant cpu sync to fix
> cacheline EEXIST warning
>
> > >
> > > When CONFIG_DMA_API_DEBUG_SG is enabled, importing a udmabuf
> > into a DRM
> > > driver (e.g. amdgpu for video playback in GNOME Videos / Showtime)
> > > triggers a spurious warning:
> > >
> > > DMA-API: amdgpu 0000:03:00.0: cacheline tracking EEXIST, \
> > > overlapping mappings aren't supported
> > > WARNING: kernel/dma/debug.c:619 at add_dma_entry+0x473/0x5f0
> > >
> > > The call chain is:
> > >
> > > amdgpu_cs_ioctl
> > > -> amdgpu_ttm_backend_bind
> > > -> dma_buf_map_attachment
> > > -> [udmabuf] map_udmabuf -> get_sg_table
> > > -> dma_map_sgtable(dev, sg, direction, 0) // attrs=0
> > > -> debug_dma_map_sg -> add_dma_entry -> EEXIST
> > >
> > > This happens because udmabuf builds a per-page scatter-gather list
> > via
> > > sg_set_folio(). When begin_cpu_udmabuf() has already created an sg
> > > table mapped for the misc device, and an importer such as amdgpu
> > maps
> > > the same pages for its own device via map_udmabuf(), the DMA
> > debug
> > > infrastructure sees two active mappings whose physical addresses
> > share
> > > cacheline boundaries and warns about the overlap.
> > >
> > > The DMA_ATTR_SKIP_CPU_SYNC flag suppresses this check in
> > > add_dma_entry() because it signals that no CPU cache maintenance is
> > > performed at map/unmap time, making the cacheline overlap
> > harmless.
> > >
> > > All other major dma-buf exporters already pass this flag:
> > > - drm_gem_map_dma_buf() passes DMA_ATTR_SKIP_CPU_SYNC
> > > - amdgpu_dma_buf_map() passes DMA_ATTR_SKIP_CPU_SYNC
> > >
> > > The CPU sync at map/unmap time is also redundant for udmabuf:
> > > begin_cpu_udmabuf() and end_cpu_udmabuf() already perform
> > explicit
> > > cache synchronization via dma_sync_sgtable_for_cpu/device() when
> > CPU
> > > access is requested through the dma-buf interface.
> > >
> > > Pass DMA_ATTR_SKIP_CPU_SYNC to dma_map_sgtable() and
> > > dma_unmap_sgtable() in udmabuf to suppress the spurious warning
> > and
> > > skip the redundant sync.
> > >
> > > Fixes: 284562e1f348 ("udmabuf: implement
> > begin_cpu_access/end_cpu_access hooks")
> > > Cc: stable@vger.kernel.org
> > > Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
> > > ---
> > > drivers/dma-buf/udmabuf.c | 4 ++--
> > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> > > index 94b8ecb892bb..9c6f8785a28a 100644
> > > --- a/drivers/dma-buf/udmabuf.c
> > > +++ b/drivers/dma-buf/udmabuf.c
> > > @@ -162,7 +162,7 @@ static struct sg_table *get_sg_table(struct
> > device *dev, struct dma_buf *buf,
> > > sg_set_folio(sgl, ubuf->folios[i], PAGE_SIZE,
> > > ubuf->offsets[i]);
> > >
> > > - ret = dma_map_sgtable(dev, sg, direction, 0);
> > > + ret = dma_map_sgtable(dev, sg, direction,
> > DMA_ATTR_SKIP_CPU_SYNC);
> > > if (ret < 0)
> > > goto err_map;
> > > return sg;
> > > @@ -177,7 +177,7 @@ static struct sg_table *get_sg_table(struct
> > device *dev, struct dma_buf *buf,
> > > static void put_sg_table(struct device *dev, struct sg_table *sg,
> > > enum dma_data_direction direction)
> > > {
> > > - dma_unmap_sgtable(dev, sg, direction, 0);
> > > + dma_unmap_sgtable(dev, sg, direction,
> > DMA_ATTR_SKIP_CPU_SYNC);
> > > sg_free_table(sg);
> > > kfree(sg);
> > > }
> > > --
> > > 2.53.0
> > >
> >
> > Gentle ping on this patch.
> >
> > To summarize the review so far:
> > Vivek: "Looks OK to me"
> > Christian: Acked-by
> >
> > Note: while my separate dma-debug patch [1] would also suppress
> > this specific warning on x86, the udmabuf fix here is still
> > valuable as it removes the redundant CPU sync at map/unmap time
> > and aligns udmabuf with other dma-buf exporters that already
> > pass DMA_ATTR_SKIP_CPU_SYNC.
> >
> > [1] https://lore.kernel.org/all/20260327124156.24820-1-
> > mikhail.v.gavrilov@gmail.com/
> >
> > Gerd, could you take a look when you have a chance?
> I am convinced that this patch is useful in some cases, so I'll add
> Christian's
> Ack and push it (into drm-misc-next) in a day or two.
I ran into a merge conflict while applying this patch on top of other
udmabuf patches. So, please resend this patch after rebasing on top
of drm-tip:
https://gitlab.freedesktop.org/drm/tip/-/commits/drm-tip?ref_type=HEADS
Thanks,
Vivek
>
> Thanks,
> Vivek
>
> >
> > --
> > Best Regards,
> > Mike Gavrilov.
Hi Mikhail,
> Subject: [PATCH] dma-buf/udmabuf: skip redundant cpu sync to fix
> cacheline EEXIST warning
>
> When CONFIG_DMA_API_DEBUG_SG is enabled, importing a udmabuf
> into a DRM
> driver (e.g. amdgpu for video playback in GNOME Videos / Showtime)
> triggers a spurious warning:
>
> DMA-API: amdgpu 0000:03:00.0: cacheline tracking EEXIST, \
> overlapping mappings aren't supported
> WARNING: kernel/dma/debug.c:619 at add_dma_entry+0x473/0x5f0
>
> The call chain is:
>
> amdgpu_cs_ioctl
> -> amdgpu_ttm_backend_bind
> -> dma_buf_map_attachment
> -> [udmabuf] map_udmabuf -> get_sg_table
> -> dma_map_sgtable(dev, sg, direction, 0) // attrs=0
> -> debug_dma_map_sg -> add_dma_entry -> EEXIST
>
> This happens because udmabuf builds a per-page scatter-gather list via
> sg_set_folio(). When begin_cpu_udmabuf() has already created an sg
> table mapped for the misc device, and an importer such as amdgpu
> maps
> the same pages for its own device via map_udmabuf(), the DMA debug
> infrastructure sees two active mappings whose physical addresses share
> cacheline boundaries and warns about the overlap.
>
> The DMA_ATTR_SKIP_CPU_SYNC flag suppresses this check in
> add_dma_entry() because it signals that no CPU cache maintenance is
> performed at map/unmap time, making the cacheline overlap harmless.
>
> All other major dma-buf exporters already pass this flag:
> - drm_gem_map_dma_buf() passes DMA_ATTR_SKIP_CPU_SYNC
> - amdgpu_dma_buf_map() passes DMA_ATTR_SKIP_CPU_SYNC
>
> The CPU sync at map/unmap time is also redundant for udmabuf:
> begin_cpu_udmabuf() and end_cpu_udmabuf() already perform explicit
> cache synchronization via dma_sync_sgtable_for_cpu/device() when
> CPU
> access is requested through the dma-buf interface.
>
> Pass DMA_ATTR_SKIP_CPU_SYNC to dma_map_sgtable() and
> dma_unmap_sgtable() in udmabuf to suppress the spurious warning
> and
> skip the redundant sync.
>
> Fixes: 284562e1f348 ("udmabuf: implement
> begin_cpu_access/end_cpu_access hooks")
> Cc: stable@vger.kernel.org
> Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
> ---
> drivers/dma-buf/udmabuf.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index 94b8ecb892bb..9c6f8785a28a 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -162,7 +162,7 @@ static struct sg_table *get_sg_table(struct device
> *dev, struct dma_buf *buf,
> sg_set_folio(sgl, ubuf->folios[i], PAGE_SIZE,
> ubuf->offsets[i]);
>
> - ret = dma_map_sgtable(dev, sg, direction, 0);
> + ret = dma_map_sgtable(dev, sg, direction,
> DMA_ATTR_SKIP_CPU_SYNC);
> if (ret < 0)
> goto err_map;
> return sg;
> @@ -177,7 +177,7 @@ static struct sg_table *get_sg_table(struct device
> *dev, struct dma_buf *buf,
> static void put_sg_table(struct device *dev, struct sg_table *sg,
> enum dma_data_direction direction)
> {
> - dma_unmap_sgtable(dev, sg, direction, 0);
> + dma_unmap_sgtable(dev, sg, direction,
> DMA_ATTR_SKIP_CPU_SYNC);
Looks OK to me but it would be nice if Christian or someone else can
provide an Ack for this patch.
Thanks,
Vivek
> sg_free_table(sg);
> kfree(sg);
> }
> --
> 2.53.0
On 3/18/26 06:40, Kasireddy, Vivek wrote:
> Hi Mikhail,
>
>> Subject: [PATCH] dma-buf/udmabuf: skip redundant cpu sync to fix
>> cacheline EEXIST warning
>>
>> When CONFIG_DMA_API_DEBUG_SG is enabled, importing a udmabuf
>> into a DRM
>> driver (e.g. amdgpu for video playback in GNOME Videos / Showtime)
>> triggers a spurious warning:
>>
>> DMA-API: amdgpu 0000:03:00.0: cacheline tracking EEXIST, \
>> overlapping mappings aren't supported
>> WARNING: kernel/dma/debug.c:619 at add_dma_entry+0x473/0x5f0
>>
>> The call chain is:
>>
>> amdgpu_cs_ioctl
>> -> amdgpu_ttm_backend_bind
>> -> dma_buf_map_attachment
>> -> [udmabuf] map_udmabuf -> get_sg_table
>> -> dma_map_sgtable(dev, sg, direction, 0) // attrs=0
>> -> debug_dma_map_sg -> add_dma_entry -> EEXIST
>>
>> This happens because udmabuf builds a per-page scatter-gather list via
>> sg_set_folio(). When begin_cpu_udmabuf() has already created an sg
>> table mapped for the misc device, and an importer such as amdgpu
>> maps
>> the same pages for its own device via map_udmabuf(), the DMA debug
>> infrastructure sees two active mappings whose physical addresses share
>> cacheline boundaries and warns about the overlap.
>>
>> The DMA_ATTR_SKIP_CPU_SYNC flag suppresses this check in
>> add_dma_entry() because it signals that no CPU cache maintenance is
>> performed at map/unmap time, making the cacheline overlap harmless.
>>
>> All other major dma-buf exporters already pass this flag:
>> - drm_gem_map_dma_buf() passes DMA_ATTR_SKIP_CPU_SYNC
>> - amdgpu_dma_buf_map() passes DMA_ATTR_SKIP_CPU_SYNC
>>
>> The CPU sync at map/unmap time is also redundant for udmabuf:
>> begin_cpu_udmabuf() and end_cpu_udmabuf() already perform explicit
>> cache synchronization via dma_sync_sgtable_for_cpu/device() when
>> CPU
>> access is requested through the dma-buf interface.
>>
>> Pass DMA_ATTR_SKIP_CPU_SYNC to dma_map_sgtable() and
>> dma_unmap_sgtable() in udmabuf to suppress the spurious warning
>> and
>> skip the redundant sync.
>>
>> Fixes: 284562e1f348 ("udmabuf: implement
>> begin_cpu_access/end_cpu_access hooks")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
>> ---
>> drivers/dma-buf/udmabuf.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
>> index 94b8ecb892bb..9c6f8785a28a 100644
>> --- a/drivers/dma-buf/udmabuf.c
>> +++ b/drivers/dma-buf/udmabuf.c
>> @@ -162,7 +162,7 @@ static struct sg_table *get_sg_table(struct device
>> *dev, struct dma_buf *buf,
>> sg_set_folio(sgl, ubuf->folios[i], PAGE_SIZE,
>> ubuf->offsets[i]);
>>
>> - ret = dma_map_sgtable(dev, sg, direction, 0);
>> + ret = dma_map_sgtable(dev, sg, direction,
>> DMA_ATTR_SKIP_CPU_SYNC);
>> if (ret < 0)
>> goto err_map;
>> return sg;
>> @@ -177,7 +177,7 @@ static struct sg_table *get_sg_table(struct device
>> *dev, struct dma_buf *buf,
>> static void put_sg_table(struct device *dev, struct sg_table *sg,
>> enum dma_data_direction direction)
>> {
>> - dma_unmap_sgtable(dev, sg, direction, 0);
>> + dma_unmap_sgtable(dev, sg, direction,
>> DMA_ATTR_SKIP_CPU_SYNC);
> Looks OK to me but it would be nice if Christian or someone else can
> provide an Ack for this patch.
The details of the udmabuf handling is absolutely not my field of expertise.
Feel free to add my Acked-by since it obviously seems to fix a bug, but it would be nice if somebody could do an in deep review as well.
Regards,
Christian.
>
> Thanks,
> Vivek
>
>> sg_free_table(sg);
>> kfree(sg);
>> }
>> --
>> 2.53.0
>
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