[PATCH v2] udmabuf: add vmap method to udmabuf_ops

[PATCH v2] udmabuf: add vmap method to udmabuf_ops

[Lukasz Wiecaszek]

The reason behind that patch is associated with videobuf2 subsystem
(or more genrally with v4l2 framework) and user created
dma buffers (udmabuf). In some circumstances
when dealing with V4L2_MEMORY_DMABUF buffers videobuf2 subsystem
wants to use dma_buf_vmap() method on the attached dma buffer.
As udmabuf does not have .vmap operation implemented,
such dma_buf_vmap() natually fails.

videobuf2_common: [cap-000000003473b2f1] __vb2_queue_alloc: allocated 3 buffers, 1 plane(s) each
videobuf2_common: [cap-000000003473b2f1] __prepare_dmabuf: buffer for plane 0 changed
videobuf2_common: [cap-000000003473b2f1] __prepare_dmabuf: failed to map dmabuf for plane 0
videobuf2_common: [cap-000000003473b2f1] __buf_prepare: buffer preparation failed: -14

The patch itself seems to be strighforward.
It adds implementation of .vmap method to 'struct dma_buf_ops udmabuf_ops'.
.vmap method itself uses vm_map_ram() to map pages linearly
into the kernel virtual address space (only if such mapping
hasn't been created yet).

Signed-off-by: Lukasz Wiecaszek <lukasz.wiecaszek@gmail.com>
Reported-by: kernel test robot <lkp@intel.com>
---
v1: https://lore.kernel.org/linux-media/202211120352.G7WPASoP-lkp@intel.com/T/#t

v1 -> v2: Patch prepared and tested against 6.1.0-rc2+

 drivers/dma-buf/udmabuf.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index 2bcdb935a3ac..2ca0e3639360 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -12,6 +12,8 @@
 #include <linux/slab.h>
 #include <linux/udmabuf.h>
 #include <linux/hugetlb.h>
+#include <linux/vmalloc.h>
+#include <linux/iosys-map.h>
 
 static int list_limit = 1024;
 module_param(list_limit, int, 0644);
@@ -26,6 +28,7 @@ struct udmabuf {
 	struct page **pages;
 	struct sg_table *sg;
 	struct miscdevice *device;
+	void *vaddr;
 };
 
 static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf)
@@ -57,6 +60,21 @@ static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
 	return 0;
 }
 
+static int vmap_udmabuf(struct dma_buf *buf, struct iosys_map *map)
+{
+	struct udmabuf *ubuf = buf->priv;
+
+	if (!ubuf->vaddr) {
+		ubuf->vaddr = vm_map_ram(ubuf->pages, ubuf->pagecount, -1);
+		if (!ubuf->vaddr)
+			return -EINVAL;
+	}
+
+	iosys_map_set_vaddr(map, ubuf->vaddr);
+
+	return 0;
+}
+
 static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
 				     enum dma_data_direction direction)
 {
@@ -159,6 +177,7 @@ static const struct dma_buf_ops udmabuf_ops = {
 	.unmap_dma_buf	   = unmap_udmabuf,
 	.release	   = release_udmabuf,
 	.mmap		   = mmap_udmabuf,
+	.vmap		   = vmap_udmabuf,
 	.begin_cpu_access  = begin_cpu_udmabuf,
 	.end_cpu_access    = end_cpu_udmabuf,
 };
-- 
2.25.1

Re: [PATCH v2] udmabuf: add vmap method to udmabuf_ops

[Dmitry Osipenko]

On 11/13/22 18:05, Lukasz Wiecaszek wrote:
> The reason behind that patch is associated with videobuf2 subsystem
> (or more genrally with v4l2 framework) and user created
> dma buffers (udmabuf). In some circumstances
> when dealing with V4L2_MEMORY_DMABUF buffers videobuf2 subsystem
> wants to use dma_buf_vmap() method on the attached dma buffer.
> As udmabuf does not have .vmap operation implemented,
> such dma_buf_vmap() natually fails.
> 
> videobuf2_common: [cap-000000003473b2f1] __vb2_queue_alloc: allocated 3 buffers, 1 plane(s) each
> videobuf2_common: [cap-000000003473b2f1] __prepare_dmabuf: buffer for plane 0 changed
> videobuf2_common: [cap-000000003473b2f1] __prepare_dmabuf: failed to map dmabuf for plane 0
> videobuf2_common: [cap-000000003473b2f1] __buf_prepare: buffer preparation failed: -14
> 
> The patch itself seems to be strighforward.
> It adds implementation of .vmap method to 'struct dma_buf_ops udmabuf_ops'.
> .vmap method itself uses vm_map_ram() to map pages linearly
> into the kernel virtual address space (only if such mapping
> hasn't been created yet).
> 
> Signed-off-by: Lukasz Wiecaszek <lukasz.wiecaszek@gmail.com>
> Reported-by: kernel test robot <lkp@intel.com>
> ---
> v1: https://lore.kernel.org/linux-media/202211120352.G7WPASoP-lkp@intel.com/T/#t
> 
> v1 -> v2: Patch prepared and tested against 6.1.0-rc2+
> 
>  drivers/dma-buf/udmabuf.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index 2bcdb935a3ac..2ca0e3639360 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -12,6 +12,8 @@
>  #include <linux/slab.h>
>  #include <linux/udmabuf.h>
>  #include <linux/hugetlb.h>
> +#include <linux/vmalloc.h>
> +#include <linux/iosys-map.h>
>  
>  static int list_limit = 1024;
>  module_param(list_limit, int, 0644);
> @@ -26,6 +28,7 @@ struct udmabuf {
>  	struct page **pages;
>  	struct sg_table *sg;
>  	struct miscdevice *device;
> +	void *vaddr;
>  };
>  
>  static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf)
> @@ -57,6 +60,21 @@ static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
>  	return 0;
>  }
>  
> +static int vmap_udmabuf(struct dma_buf *buf, struct iosys_map *map)
> +{
> +	struct udmabuf *ubuf = buf->priv;
> +
> +	if (!ubuf->vaddr) {
> +		ubuf->vaddr = vm_map_ram(ubuf->pages, ubuf->pagecount, -1);
> +		if (!ubuf->vaddr)
> +			return -EINVAL;
> +	}
> +
> +	iosys_map_set_vaddr(map, ubuf->vaddr);
> +
> +	return 0;
> +}
> +
>  static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
>  				     enum dma_data_direction direction)
>  {
> @@ -159,6 +177,7 @@ static const struct dma_buf_ops udmabuf_ops = {
>  	.unmap_dma_buf	   = unmap_udmabuf,
>  	.release	   = release_udmabuf,
>  	.mmap		   = mmap_udmabuf,
> +	.vmap		   = vmap_udmabuf,
>  	.begin_cpu_access  = begin_cpu_udmabuf,
>  	.end_cpu_access    = end_cpu_udmabuf,
>  };

Where is vunmap?

-- 
Best regards,
Dmitry

Re: [PATCH v2] udmabuf: add vmap method to udmabuf_ops

[Dmitry Osipenko]

On 11/13/22 18:05, Lukasz Wiecaszek wrote:
> +static int vmap_udmabuf(struct dma_buf *buf, struct iosys_map *map)
> +{
> +	struct udmabuf *ubuf = buf->priv;
> +
> +	if (!ubuf->vaddr) {
> +		ubuf->vaddr = vm_map_ram(ubuf->pages, ubuf->pagecount, -1);
> +		if (!ubuf->vaddr)
> +			return -EINVAL;
> +	}

Create a new mapping on each vmap_udmabuf() and add the corresponding
vunmap.

Otherwise persistent vmapping shall be released together with udmabuf.
It doesn't look that persistent vmapping is needed for udmabufs.

-- 
Best regards,
Dmitry

Re: [PATCH v2] udmabuf: add vmap method to udmabuf_ops

[Lukasz Wiecaszek]

On Sun, Nov 13, 2022 at 07:35:20PM +0300, Dmitry Osipenko wrote:
> On 11/13/22 18:05, Lukasz Wiecaszek wrote:
> > +static int vmap_udmabuf(struct dma_buf *buf, struct iosys_map *map)
> > +{
> > +	struct udmabuf *ubuf = buf->priv;
> > +
> > +	if (!ubuf->vaddr) {
> > +		ubuf->vaddr = vm_map_ram(ubuf->pages, ubuf->pagecount, -1);
> > +		if (!ubuf->vaddr)
> > +			return -EINVAL;
> > +	}
> 
> Create a new mapping on each vmap_udmabuf() and add the corresponding
> vunmap.
> 
> Otherwise persistent vmapping shall be released together with udmabuf.
> It doesn't look that persistent vmapping is needed for udmabufs.
> 
> -- 
> Best regards,
> Dmitry

Right. Thanks for review and remarks. Adding vunmap sounds reasonable to
me. Will add it somehow this week.

Regards,
Lukasz