[PATCH v2 1/1] drm/amdgpu: Add gem_prime_mmap support

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> -----Original Message-----
> From: amd-gfx [mailto:amd-gfx-bounces at lists.freedesktop.org] On Behalf
> Of Li, Samuel
> Sent: Wednesday, September 20, 2017 11:44 AM
> To: Koenig, Christian; amd-gfx at lists.freedesktop.org
> Subject: RE: [PATCH v2 1/1] drm/amdgpu: Add gem_prime_mmap support
> 
> > What happens when another thread is using amdgpu_dmabuf_ops to call
> > begin_cpu_access/end_cpu_access when you are fixing it up again?
> Right, that is an issue.
> 
> > I would just completely drop the two callbacks, pinning is not necessary for
> > CPU access and thinking more about it it actually has some unwanted side
> > effects.
> CPU access needs synchronization anyway, so the two callbacks cannot be
> dropped (other drivers implemented too), so I would like to keep it there for
> now.

Pinning only needs to happen for device access (i.e., so the pages don't get swapped out).

Alex

> 
> Sam
> 
> 
> > -----Original Message-----
> > From: Koenig, Christian
> > Sent: Wednesday, September 20, 2017 2:58 AM
> > To: Li, Samuel <Samuel.Li at amd.com>; amd-gfx at lists.freedesktop.org
> > Subject: Re: [PATCH v2 1/1] drm/amdgpu: Add gem_prime_mmap support
> >
> > > What do you mean "This isn't race free"?
> >
> > Take a look at the code again:
> > > +    dma_buf = drm_gem_prime_export(dev, gobj, flags);
> > > +    amdgpu_dmabuf_ops = *(dma_buf->ops);
> > > +    amdgpu_dmabuf_ops.begin_cpu_access =
> > amdgpu_gem_begin_cpu_access;
> > > +    amdgpu_dmabuf_ops.end_cpu_access =
> > amdgpu_gem_end_cpu_access;
> > > +    dma_buf->ops = &amdgpu_dmabuf_ops;
> >
> > What happens when another thread is using amdgpu_dmabuf_ops to call
> > begin_cpu_access/end_cpu_access when you are fixing it up again?
> >
> > I would just completely drop the two callbacks, pinning is not necessary for
> > CPU access and thinking more about it it actually has some unwanted side
> > effects.
> >
> > Regards,
> > Christian.
> >
> > Am 19.09.2017 um 23:22 schrieb Samuel Li:
> > >>> +    vma->vm_pgoff = amdgpu_bo_mmap_offset(bo) >> PAGE_SHIFT;
> > >> Maybe better use "vma->vm_pgoff += amdgpu_bo_mmap_offset(bo)
> >>
> > PAGE_SHIFT;", but I'm not sure.
> > >> How other drivers handle this?
> > > This is a good catch. Looks like pgoff is honored during prime mmap, not a
> > fake offset here.
> > >
> > >>> +    dma_buf->ops = &amdgpu_dmabuf_ops;
> > >> This isn't race free and needs to be fixed.
> > >> Better add callbacks to drm_prime.c similar to
> > drm_gem_dmabuf_mmap().
> > > What do you mean "This isn't race free"?
> > >
> > > Regards,
> > > Sam
> > >
> > >
> > >
> > > On 2017-09-15 11:05 AM, Christian König wrote:
> > >> Am 14.09.2017 um 00:39 schrieb Samuel Li:
> > >>> v2: drop hdp invalidate/flush.
> > >>>
> > >>> Signed-off-by: Samuel Li <Samuel.Li at amd.com>
> > >>> ---
> > >>>    drivers/gpu/drm/amd/amdgpu/amdgpu.h       |  3 ++
> > >>>    drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c   |  3 +-
> > >>>    drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c | 77
> > ++++++++++++++++++++++++++++++-
> > >>>    3 files changed, 81 insertions(+), 2 deletions(-)
> > >>>
> > >>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> > >>> b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> > >>> index d2aaad7..188b705 100644
> > >>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> > >>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> > >>> @@ -395,11 +395,14 @@
> amdgpu_gem_prime_import_sg_table(struct
> > drm_device *dev,
> > >>>    struct dma_buf *amdgpu_gem_prime_export(struct drm_device
> *dev,
> > >>>                        struct drm_gem_object *gobj,
> > >>>                        int flags);
> > >>> +struct drm_gem_object *amdgpu_gem_prime_import(struct
> > drm_device *dev,
> > >>> +                        struct dma_buf *dma_buf);
> > >>>    int amdgpu_gem_prime_pin(struct drm_gem_object *obj);
> > >>>    void amdgpu_gem_prime_unpin(struct drm_gem_object *obj);
> > >>>    struct reservation_object *amdgpu_gem_prime_res_obj(struct
> > drm_gem_object *);
> > >>>    void *amdgpu_gem_prime_vmap(struct drm_gem_object *obj);
> > >>>    void amdgpu_gem_prime_vunmap(struct drm_gem_object *obj,
> void
> > >>> *vaddr);
> > >>> +int amdgpu_gem_prime_mmap(struct drm_gem_object *obj, struct
> > >>> +vm_area_struct *vma);
> > >>>    int amdgpu_gem_debugfs_init(struct amdgpu_device *adev);
> > >>>      /* sub-allocation manager, it has to be protected by another lock.
> > >>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > >>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > >>> index 2cdf844..9b63ac5 100644
> > >>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > >>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > >>> @@ -835,7 +835,7 @@ static struct drm_driver kms_driver = {
> > >>>        .prime_handle_to_fd = drm_gem_prime_handle_to_fd,
> > >>>        .prime_fd_to_handle = drm_gem_prime_fd_to_handle,
> > >>>        .gem_prime_export = amdgpu_gem_prime_export,
> > >>> -    .gem_prime_import = drm_gem_prime_import,
> > >>> +    .gem_prime_import = amdgpu_gem_prime_import,
> > >>>        .gem_prime_pin = amdgpu_gem_prime_pin,
> > >>>        .gem_prime_unpin = amdgpu_gem_prime_unpin,
> > >>>        .gem_prime_res_obj = amdgpu_gem_prime_res_obj, @@ -843,6
> > >>> +843,7 @@ static struct drm_driver kms_driver = {
> > >>>        .gem_prime_import_sg_table =
> > amdgpu_gem_prime_import_sg_table,
> > >>>        .gem_prime_vmap = amdgpu_gem_prime_vmap,
> > >>>        .gem_prime_vunmap = amdgpu_gem_prime_vunmap,
> > >>> +    .gem_prime_mmap = amdgpu_gem_prime_mmap,
> > >>>          .name = DRIVER_NAME,
> > >>>        .desc = DRIVER_DESC,
> > >>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c
> > >>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c
> > >>> index 5b3f928..13c977a 100644
> > >>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c
> > >>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c
> > >>> @@ -57,6 +57,40 @@ void amdgpu_gem_prime_vunmap(struct
> > drm_gem_object *obj, void *vaddr)
> > >>>        ttm_bo_kunmap(&bo->dma_buf_vmap);
> > >>>    }
> > >>>    +int amdgpu_gem_prime_mmap(struct drm_gem_object *obj,
> struct
> > >>> vm_area_struct *vma)
> > >>> +{
> > >>> +    struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
> > >>> +    struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
> > >>> +    unsigned asize = amdgpu_bo_size(bo);
> > >>> +    int ret;
> > >>> +
> > >>> +    if (!vma->vm_file)
> > >>> +        return -ENODEV;
> > >>> +
> > >>> +    if (adev == NULL)
> > >>> +        return -ENODEV;
> > >>> +
> > >>> +    /* Check for valid size. */
> > >>> +    if (asize < vma->vm_end - vma->vm_start)
> > >>> +        return -EINVAL;
> > >>> +
> > >>> +    if (amdgpu_ttm_tt_get_usermm(bo->tbo.ttm) ||
> > >>> +        (bo->flags & AMDGPU_GEM_CREATE_NO_CPU_ACCESS)) {
> > >>> +        return -EPERM;
> > >>> +    }
> > >>> +    vma->vm_pgoff = amdgpu_bo_mmap_offset(bo) >> PAGE_SHIFT;
> > >> Maybe better use "vma->vm_pgoff += amdgpu_bo_mmap_offset(bo)
> >>
> > PAGE_SHIFT;", but I'm not sure.
> > >>
> > >> How other drivers handle this?
> > >>
> > >>> +
> > >>> +    /* prime mmap does not need to check access, so allow here */
> > >>> +    ret = drm_vma_node_allow(&obj->vma_node, vma->vm_file-
> > >private_data);
> > >>> +    if (ret)
> > >>> +        return ret;
> > >>> +
> > >>> +    ret = ttm_bo_mmap(vma->vm_file, vma, &adev->mman.bdev);
> > >>> +    drm_vma_node_revoke(&obj->vma_node,
> > >>> + vma->vm_file->private_data);
> > >>> +
> > >>> +    return ret;
> > >>> +}
> > >>> +
> > >>>    struct drm_gem_object *
> > >>>    amdgpu_gem_prime_import_sg_table(struct drm_device *dev,
> > >>>                     struct dma_buf_attachment *attach, @@ -130,14
> > >>> +164,55 @@ struct reservation_object
> > *amdgpu_gem_prime_res_obj(struct drm_gem_object *obj)
> > >>>        return bo->tbo.resv;
> > >>>    }
> > >>>    +static int amdgpu_gem_begin_cpu_access(struct dma_buf
> *dma_buf,
> > >>> enum dma_data_direction direction)
> > >>> +{
> > >>> +    return amdgpu_gem_prime_pin(dma_buf->priv);
> > >>> +}
> > >>> +
> > >>> +static int amdgpu_gem_end_cpu_access(struct dma_buf *dma_buf,
> > enum
> > >>> +dma_data_direction direction) {
> > >>> +    amdgpu_gem_prime_unpin(dma_buf->priv);
> > >>> +
> > >>> +    return 0;
> > >>> +}
> > >>> +
> > >>> +static struct dma_buf_ops amdgpu_dmabuf_ops;
> > >>> +
> > >>>    struct dma_buf *amdgpu_gem_prime_export(struct drm_device
> *dev,
> > >>>                        struct drm_gem_object *gobj,
> > >>>                        int flags)
> > >>>    {
> > >>>        struct amdgpu_bo *bo = gem_to_amdgpu_bo(gobj);
> > >>> +    struct dma_buf *dma_buf;
> > >>>          if (amdgpu_ttm_tt_get_usermm(bo->tbo.ttm))
> > >>>            return ERR_PTR(-EPERM);
> > >>>    -    return drm_gem_prime_export(dev, gobj, flags);
> > >>> +    dma_buf = drm_gem_prime_export(dev, gobj, flags);
> > >>> +    amdgpu_dmabuf_ops = *(dma_buf->ops);
> > >>> +    amdgpu_dmabuf_ops.begin_cpu_access =
> > amdgpu_gem_begin_cpu_access;
> > >>> +    amdgpu_dmabuf_ops.end_cpu_access =
> > amdgpu_gem_end_cpu_access;
> > >>> +    dma_buf->ops = &amdgpu_dmabuf_ops;
> > >> This isn't race free and needs to be fixed.
> > >>
> > >> Better add callbacks to drm_prime.c similar to
> > drm_gem_dmabuf_mmap().
> > >>
> > >> Alternative you could just completely drop
> > amdgpu_gem_begin_cpu_access() and amdgpu_gem_end_cpu_access()
> as
> > well.
> > >>
> > >> When the buffer is shared between device it is pinned anyway and
> when
> > it isn't shared ttm_bo_mmap() is able to handle VRAM mappings as well.
> > >>
> > >> Regards,
> > >> Christian.
> > >>
> > >>> +
> > >>> +    return dma_buf;
> > >>> +}
> > >>> +
> > >>> +struct drm_gem_object *amdgpu_gem_prime_import(struct
> > drm_device *dev,
> > >>> +                        struct dma_buf *dma_buf) {
> > >>> +    struct drm_gem_object *obj;
> > >>> +
> > >>> +    if (dma_buf->ops == &amdgpu_dmabuf_ops) {
> > >>> +        obj = dma_buf->priv;
> > >>> +        if (obj->dev == dev) {
> > >>> +            /*
> > >>> +             * Importing dmabuf exported from out own gem increases
> > >>> +             * refcount on gem itself instead of f_count of dmabuf.
> > >>> +             */
> > >>> +            drm_gem_object_get(obj);
> > >>> +            return obj;
> > >>> +        }
> > >>> +    }
> > >>> +
> > >>> +    return drm_gem_prime_import(dev, dma_buf);
> > >>>    }
> > >>
> 
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