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

[Guenter Roeck <linux@roeck-us.net>]

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 <thomas.hellstrom@linux.intel.com>
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>

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
>