linux-kernel - Re: [RFC 10/17] drm: radeon: fix sg_table nents vs. orig

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Date:   Tue, 28 Apr 2020 17:15:16 +0200
From:   Christian König <ckoenig.leichtzumerken@...il.com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>,
        dri-devel@...ts.freedesktop.org, iommu@...ts.linux-foundation.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org
Cc:     Daniel Vetter <daniel@...ll.ch>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        David Airlie <airlied@...ux.ie>,
        intel-gfx@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
        Christoph Hellwig <hch@....de>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Robin Murphy <robin.murphy@....com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC 10/17] drm: radeon: fix sg_table nents vs. orig_nents misuse

Am 28.04.20 um 15:19 schrieb Marek Szyprowski:
> The Documentation/DMA-API-HOWTO.txt states that dma_map_sg returns the
> numer of the created entries in the DMA address space. However the
> subsequent calls to dma_sync_sg_for_{device,cpu} and dma_unmap_sg must be
> called with the original number of entries passed to dma_map_sg. The
> sg_table->nents in turn holds the result of the dma_map_sg call as stated
> in include/linux/scatterlist.h. Adapt the code to obey those rules.
>
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>

Reviewed-by: Christian König <christian.koenig@....com>

> ---
>   drivers/gpu/drm/radeon/radeon_ttm.c | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c b/drivers/gpu/drm/radeon/radeon_ttm.c
> index 5d50c9e..4770880 100644
> --- a/drivers/gpu/drm/radeon/radeon_ttm.c
> +++ b/drivers/gpu/drm/radeon/radeon_ttm.c
> @@ -481,7 +481,7 @@ static int radeon_ttm_tt_pin_userptr(struct ttm_tt *ttm)
>   {
>   	struct radeon_device *rdev = radeon_get_rdev(ttm->bdev);
>   	struct radeon_ttm_tt *gtt = (void *)ttm;
> -	unsigned pinned = 0, nents;
> +	unsigned pinned = 0;
>   	int r;
>   
>   	int write = !(gtt->userflags & RADEON_GEM_USERPTR_READONLY);
> @@ -522,8 +522,8 @@ static int radeon_ttm_tt_pin_userptr(struct ttm_tt *ttm)
>   		goto release_sg;
>   
>   	r = -ENOMEM;
> -	nents = dma_map_sg(rdev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
> -	if (nents == 0)
> +	ttm->sg->nents = dma_map_sg(rdev->dev, ttm->sg->sgl,
> +	if (ttm->sg->nents == 0)
>   		goto release_sg;
>   
>   	drm_prime_sg_to_page_addr_arrays(ttm->sg, ttm->pages,
> @@ -554,9 +554,9 @@ static void radeon_ttm_tt_unpin_userptr(struct ttm_tt *ttm)
>   		return;
>   
>   	/* free the sg table and pages again */
> -	dma_unmap_sg(rdev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
> +	dma_unmap_sg(rdev->dev, ttm->sg->sgl, ttm->sg->orig_nents, direction);
>   
> -	for_each_sg_page(ttm->sg->sgl, &sg_iter, ttm->sg->nents, 0) {
> +	for_each_sg_page(ttm->sg->sgl, &sg_iter, ttm->sg->orig_nents, 0) {
>   		struct page *page = sg_page_iter_page(&sg_iter);
>   		if (!(gtt->userflags & RADEON_GEM_USERPTR_READONLY))
>   			set_page_dirty(page);