Re: [PATCH] Revert "drm/vgem: fix cache synchronization on arm/arm64"

[Sean Paul <sean@poorly.run>]

On Thu, Aug 01, 2019 at 01:44:58PM +0100, Chris Wilson wrote:
> commit 7e9e5ead55be ("drm/vgem: fix cache synchronization on arm/arm64")
> broke all of the !llc i915-vgem coherency tests in CI, and left the HW
> very, very unhappy (which is even more scary).
> 
> Fixes: 7e9e5ead55be ("drm/vgem: fix cache synchronization on arm/arm64")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

Acked-by: Sean Paul <sean@poorly.run>

> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Rob Clark <robdclark@chromium.org>
> Cc: Sean Paul <seanpaul@chromium.org>
> ---
>  drivers/gpu/drm/vgem/vgem_drv.c | 130 ++++++++++++--------------------
>  1 file changed, 47 insertions(+), 83 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c
> index b98689fb0d5d..5bd60ded3d81 100644
> --- a/drivers/gpu/drm/vgem/vgem_drv.c
> +++ b/drivers/gpu/drm/vgem/vgem_drv.c
> @@ -54,16 +54,10 @@ static struct vgem_device {
>  	struct platform_device *platform;
>  } *vgem_device;
>  
> -static void sync_and_unpin(struct drm_vgem_gem_object *bo);
> -static struct page **pin_and_sync(struct drm_vgem_gem_object *bo);
> -
>  static void vgem_gem_free_object(struct drm_gem_object *obj)
>  {
>  	struct drm_vgem_gem_object *vgem_obj = to_vgem_bo(obj);
>  
> -	if (!obj->import_attach)
> -		sync_and_unpin(vgem_obj);
> -
>  	kvfree(vgem_obj->pages);
>  	mutex_destroy(&vgem_obj->pages_lock);
>  
> @@ -91,15 +85,40 @@ static vm_fault_t vgem_gem_fault(struct vm_fault *vmf)
>  		return VM_FAULT_SIGBUS;
>  
>  	mutex_lock(&obj->pages_lock);
> -	if (!obj->pages)
> -		pin_and_sync(obj);
>  	if (obj->pages) {
>  		get_page(obj->pages[page_offset]);
>  		vmf->page = obj->pages[page_offset];
>  		ret = 0;
>  	}
>  	mutex_unlock(&obj->pages_lock);
> +	if (ret) {
> +		struct page *page;
> +
> +		page = shmem_read_mapping_page(
> +					file_inode(obj->base.filp)->i_mapping,
> +					page_offset);
> +		if (!IS_ERR(page)) {
> +			vmf->page = page;
> +			ret = 0;
> +		} else switch (PTR_ERR(page)) {
> +			case -ENOSPC:
> +			case -ENOMEM:
> +				ret = VM_FAULT_OOM;
> +				break;
> +			case -EBUSY:
> +				ret = VM_FAULT_RETRY;
> +				break;
> +			case -EFAULT:
> +			case -EINVAL:
> +				ret = VM_FAULT_SIGBUS;
> +				break;
> +			default:
> +				WARN_ON(PTR_ERR(page));
> +				ret = VM_FAULT_SIGBUS;
> +				break;
> +		}
>  
> +	}
>  	return ret;
>  }
>  
> @@ -265,93 +284,32 @@ static const struct file_operations vgem_driver_fops = {
>  	.release	= drm_release,
>  };
>  
> -/* Called under pages_lock, except in free path (where it can't race): */
> -static void sync_and_unpin(struct drm_vgem_gem_object *bo)
> -{
> -	struct drm_device *dev = bo->base.dev;
> -
> -	if (bo->table) {
> -		dma_sync_sg_for_cpu(dev->dev, bo->table->sgl,
> -				bo->table->nents, DMA_BIDIRECTIONAL);
> -		sg_free_table(bo->table);
> -		kfree(bo->table);
> -		bo->table = NULL;
> -	}
> -
> -	if (bo->pages) {
> -		drm_gem_put_pages(&bo->base, bo->pages, true, true);
> -		bo->pages = NULL;
> -	}
> -}
> -
> -static struct page **pin_and_sync(struct drm_vgem_gem_object *bo)
> -{
> -	struct drm_device *dev = bo->base.dev;
> -	int npages = bo->base.size >> PAGE_SHIFT;
> -	struct page **pages;
> -	struct sg_table *sgt;
> -
> -	WARN_ON(!mutex_is_locked(&bo->pages_lock));
> -
> -	pages = drm_gem_get_pages(&bo->base);
> -	if (IS_ERR(pages)) {
> -		bo->pages_pin_count--;
> -		mutex_unlock(&bo->pages_lock);
> -		return pages;
> -	}
> -
> -	sgt = drm_prime_pages_to_sg(pages, npages);
> -	if (IS_ERR(sgt)) {
> -		dev_err(dev->dev,
> -			"failed to allocate sgt: %ld\n",
> -			PTR_ERR(bo->table));
> -		drm_gem_put_pages(&bo->base, pages, false, false);
> -		mutex_unlock(&bo->pages_lock);
> -		return ERR_CAST(bo->table);
> -	}
> -
> -	/*
> -	 * Flush the object from the CPU cache so that importers
> -	 * can rely on coherent indirect access via the exported
> -	 * dma-address.
> -	 */
> -	dma_sync_sg_for_device(dev->dev, sgt->sgl,
> -			sgt->nents, DMA_BIDIRECTIONAL);
> -
> -	bo->pages = pages;
> -	bo->table = sgt;
> -
> -	return pages;
> -}
> -
>  static struct page **vgem_pin_pages(struct drm_vgem_gem_object *bo)
>  {
> -	struct page **pages;
> -
>  	mutex_lock(&bo->pages_lock);
> -	if (bo->pages_pin_count++ == 0 && !bo->pages) {
> -		pages = pin_and_sync(bo);
> -	} else {
> -		WARN_ON(!bo->pages);
> -		pages = bo->pages;
> +	if (bo->pages_pin_count++ == 0) {
> +		struct page **pages;
> +
> +		pages = drm_gem_get_pages(&bo->base);
> +		if (IS_ERR(pages)) {
> +			bo->pages_pin_count--;
> +			mutex_unlock(&bo->pages_lock);
> +			return pages;
> +		}
> +
> +		bo->pages = pages;
>  	}
>  	mutex_unlock(&bo->pages_lock);
>  
> -	return pages;
> +	return bo->pages;
>  }
>  
>  static void vgem_unpin_pages(struct drm_vgem_gem_object *bo)
>  {
> -	/*
> -	 * We shouldn't hit this for imported bo's.. in the import
> -	 * case we don't own the scatter-table
> -	 */
> -	WARN_ON(bo->base.import_attach);
> -
>  	mutex_lock(&bo->pages_lock);
>  	if (--bo->pages_pin_count == 0) {
> -		WARN_ON(!bo->table);
> -		sync_and_unpin(bo);
> +		drm_gem_put_pages(&bo->base, bo->pages, true, true);
> +		bo->pages = NULL;
>  	}
>  	mutex_unlock(&bo->pages_lock);
>  }
> @@ -359,12 +317,18 @@ static void vgem_unpin_pages(struct drm_vgem_gem_object *bo)
>  static int vgem_prime_pin(struct drm_gem_object *obj)
>  {
>  	struct drm_vgem_gem_object *bo = to_vgem_bo(obj);
> +	long n_pages = obj->size >> PAGE_SHIFT;
>  	struct page **pages;
>  
>  	pages = vgem_pin_pages(bo);
>  	if (IS_ERR(pages))
>  		return PTR_ERR(pages);
>  
> +	/* Flush the object from the CPU cache so that importers can rely
> +	 * on coherent indirect access via the exported dma-address.
> +	 */
> +	drm_clflush_pages(pages, n_pages);
> +
>  	return 0;
>  }
>  
> -- 
> 2.23.0.rc0
> 
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-- 
Sean Paul, Software Engineer, Google / Chromium OS
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