Re: [Intel-gfx] [PATCH 4/9] drm/i915/dmabuf: add paranoid flush-on-acquire

[Guenter Roeck]

On Mon, Oct 18, 2021 at 06:45:03PM +0100, Matthew Auld wrote:
> As pointed out by Thomas, we likely need to flush the pages here if the
> GPU can read the page contents directly from main memory. Underneath we
> don't know what the sg_table is pointing to, so just add a
> wbinvd_on_all_cpus() here, for now.
> 
> Reported-by: Thomas Hellström 
> Signed-off-by: Matthew Auld 
> Cc: Thomas Hellström 

With nosmp builds:

Error log:
drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c: In function 
'i915_gem_object_get_pages_dmabuf':
drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c:248:17: error: implicit declaration 
of function 'wbinvd_on_all_cpus' [-Werror=implicit-function-declaration]
  248 | wbinvd_on_all_cpus();
  | ^~

Guenter

> ---
>  drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 6 +-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c 
> b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> index 5be505ebbb7b..1adcd8e02d29 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> @@ -232,6 +232,7 @@ struct dma_buf *i915_gem_prime_export(struct 
> drm_gem_object *gem_obj, int flags)
>  
>  static int i915_gem_object_get_pages_dmabuf(struct drm_i915_gem_object *obj)
>  {
> + struct drm_i915_private *i915 = to_i915(obj->base.dev);
>   struct sg_table *pages;
>   unsigned int sg_page_sizes;
>  
> @@ -242,8 +243,11 @@ static int i915_gem_object_get_pages_dmabuf(struct 
> drm_i915_gem_object *obj)
>   if (IS_ERR(pages))
>   return PTR_ERR(pages);
>  
> - sg_page_sizes = i915_sg_dma_sizes(pages->sgl);
> + /* XXX: consider doing a vmap flush or something */
> + if (!HAS_LLC(i915) || i915_gem_object_can_bypass_llc(obj))
> + wbinvd_on_all_cpus();
>  
> + sg_page_sizes = i915_sg_dma_sizes(pages->sgl);
>   __i915_gem_object_set_pages(obj, pages, sg_page_sizes);
>  
>   return 0;
> -- 
> 2.26.3
> 

Re: [Intel-gfx] [PATCH 4/9] drm/i915/dmabuf: add paranoid flush-on-acquire

[Thomas Hellström]

On Mon, 2021-10-18 at 18:45 +0100, Matthew Auld wrote:
> As pointed out by Thomas, we likely need to flush the pages here if
> the
> GPU can read the page contents directly from main memory. Underneath
> we
> don't know what the sg_table is pointing to, so just add a
> wbinvd_on_all_cpus() here, for now.
> 
> Reported-by: Thomas Hellström 
> Signed-off-by: Matthew Auld 
> Cc: Thomas Hellström 

Reviewed-by: Thomas Hellström 

[Intel-gfx] [PATCH 4/9] drm/i915/dmabuf: add paranoid flush-on-acquire

[Matthew Auld]

As pointed out by Thomas, we likely need to flush the pages here if the
GPU can read the page contents directly from main memory. Underneath we
don't know what the sg_table is pointing to, so just add a
wbinvd_on_all_cpus() here, for now.

Reported-by: Thomas Hellström 
Signed-off-by: Matthew Auld 
Cc: Thomas Hellström 
---
 drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 6 +-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c 
b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
index 5be505ebbb7b..1adcd8e02d29 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
@@ -232,6 +232,7 @@ struct dma_buf *i915_gem_prime_export(struct drm_gem_object 
*gem_obj, int flags)
 
 static int i915_gem_object_get_pages_dmabuf(struct drm_i915_gem_object *obj)
 {
+   struct drm_i915_private *i915 = to_i915(obj->base.dev);
struct sg_table *pages;
unsigned int sg_page_sizes;
 
@@ -242,8 +243,11 @@ static int i915_gem_object_get_pages_dmabuf(struct 
drm_i915_gem_object *obj)
if (IS_ERR(pages))
return PTR_ERR(pages);
 
-   sg_page_sizes = i915_sg_dma_sizes(pages->sgl);
+   /* XXX: consider doing a vmap flush or something */
+   if (!HAS_LLC(i915) || i915_gem_object_can_bypass_llc(obj))
+   wbinvd_on_all_cpus();
 
+   sg_page_sizes = i915_sg_dma_sizes(pages->sgl);
__i915_gem_object_set_pages(obj, pages, sg_page_sizes);
 
return 0;
-- 
2.26.3