Re: [bug report] drm/ttm: add transparent huge page support for DMA allocations v2

["Koenig, Christian" <Christian.Koenig@amd.com>]

Am 27.06.19 um 16:06 schrieb Dan Carpenter:
> Hello Christian König,
>
> The patch 648bc3574716: "drm/ttm: add transparent huge page support
> for DMA allocations v2" from Jul 6, 2017, leads to the following
> static checker warning:
>
> 	drivers/gpu/drm/ttm/ttm_page_alloc_dma.c:314 __ttm_dma_alloc_page()
> 	error: 'vaddr' came from dma_alloc_coherent() so we can't do virt_to_phys()
>
> drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
>     295  static struct dma_page *__ttm_dma_alloc_page(struct dma_pool *pool)
>     296  {
>     297          struct dma_page *d_page;
>     298          unsigned long attrs = 0;
>     299          void *vaddr;
>     300
>     301          d_page = kmalloc(sizeof(struct dma_page), GFP_KERNEL);
>     302          if (!d_page)
>     303                  return NULL;
>     304
>     305          if (pool->type & IS_HUGE)
>     306                  attrs = DMA_ATTR_NO_WARN;
>     307
>     308          vaddr = dma_alloc_attrs(pool->dev, pool->size, &d_page->dma,
>     309                                  pool->gfp_flags, attrs);
>     310          if (vaddr) {
>     311                  if (is_vmalloc_addr(vaddr))
>     312                          d_page->p = vmalloc_to_page(vaddr);
>     313                  else
>     314                          d_page->p = virt_to_page(vaddr);
>
> Christoph was explaining this earlier and I don't think it's sufficient
> to just check is_vmalloc_addr().  See https://lkml.org/lkml/2019/6/17/155
> Apparently the vaddr might not have a page backing...

That stuff was copied from the older non-huge page code and I actually 
think it is correct.

If not then the real question is how to correctly get the backing page 
from dma_alloc_attrs().

Christian.

>
> (I am a newbie to this so I may be wrong or have misunderstood also).
>
>     315                  d_page->vaddr = (unsigned long)vaddr;
>     316                  if (pool->type & IS_HUGE)
>     317                          d_page->vaddr |= VADDR_FLAG_HUGE_POOL;
>     318          } else {
>     319                  kfree(d_page);
>     320                  d_page = NULL;
>     321          }
>     322          return d_page;
>     323  }
>
> regards,
> dan carpenter

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