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

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Aug 02, 2019 at 10:18:10AM -0400, Sean Paul wrote:
> 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>

Applied to drm-fixes directly.

Thanks, Daniel

> 
> > 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
> > 
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Sean Paul, Software Engineer, Google / Chromium OS

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx