2019-02-04 18:39:41

by Gerd Hoffmann

Subject: [PATCH] drm/bochs: fix bochs_gem_prime_mmap

ttm_fbdev_mmap() just doesn't work. It appears to work fine, mmap()
returns success, but any attempt to actually access the mapping causes a
SIGBUS.

We can just use drm_gem_prime_mmap() instead. Almost. We have to copy
over the start offset from the ttm_buffer_object vm_node to the
drm_gem_object vm_node so the offset math in drm_gem_prime_mmap() works
correctly for us even though we use ttm to manage our objects.

Signed-off-by: Gerd Hoffmann <[email protected]>
---
drivers/gpu/drm/bochs/bochs_mm.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bochs/bochs_mm.c b/drivers/gpu/drm/bochs/bochs_mm.c
index 641a33f134..49463348a0 100644
--- a/drivers/gpu/drm/bochs/bochs_mm.c
+++ b/drivers/gpu/drm/bochs/bochs_mm.c
@@ -442,5 +442,6 @@ int bochs_gem_prime_mmap(struct drm_gem_object *obj,
{
struct bochs_bo *bo = gem_to_bochs_bo(obj);

- return ttm_fbdev_mmap(vma, &bo->bo);
+ bo->gem.vma_node.vm_node.start = bo->bo.vma_node.vm_node.start;
+ return drm_gem_prime_mmap(obj, vma);
}
--
2.9.3

2019-02-05 09:02:17

by Daniel Vetter

Subject: Re: [PATCH] drm/bochs: fix bochs_gem_prime_mmap

On Mon, Feb 04, 2019 at 07:38:58PM +0100, Gerd Hoffmann wrote:
> ttm_fbdev_mmap() just doesn't work. It appears to work fine, mmap()
> returns success, but any attempt to actually access the mapping causes a
> SIGBUS.
>
> We can just use drm_gem_prime_mmap() instead. Almost. We have to copy
> over the start offset from the ttm_buffer_object vm_node to the
> drm_gem_object vm_node so the offset math in drm_gem_prime_mmap() works
> correctly for us even though we use ttm to manage our objects.
>
> Signed-off-by: Gerd Hoffmann <[email protected]>

Would be kinda neat if we could teach ttm to not have it's own vma node
...

Anyway, lgtm.

Reviewed-by: Daniel Vetter <[email protected]>

> ---
> drivers/gpu/drm/bochs/bochs_mm.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/bochs/bochs_mm.c b/drivers/gpu/drm/bochs/bochs_mm.c
> index 641a33f134..49463348a0 100644
> --- a/drivers/gpu/drm/bochs/bochs_mm.c
> +++ b/drivers/gpu/drm/bochs/bochs_mm.c
> @@ -442,5 +442,6 @@ int bochs_gem_prime_mmap(struct drm_gem_object *obj,
> {
> struct bochs_bo *bo = gem_to_bochs_bo(obj);
>
> - return ttm_fbdev_mmap(vma, &bo->bo);
> + bo->gem.vma_node.vm_node.start = bo->bo.vma_node.vm_node.start;
> + return drm_gem_prime_mmap(obj, vma);
> }
> --
> 2.9.3
>

--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch