linux-kernel - [RFC 08/17] drm: msm: fix sg_table nents vs. orig

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Message-Id: <20200428132005.21424-9-m.szyprowski@samsung.com>
Date:   Tue, 28 Apr 2020 15:19:56 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     dri-devel@...ts.freedesktop.org, iommu@...ts.linux-foundation.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Christoph Hellwig <hch@....de>,
        Robin Murphy <robin.murphy@....com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        intel-gfx@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        amd-gfx@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Subject: [RFC 08/17] drm: msm: fix sg_table nents vs. orig_nents misuse

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>
---
 drivers/gpu/drm/msm/msm_gem.c   | 8 ++++----
 drivers/gpu/drm/msm/msm_iommu.c | 3 ++-
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 5a6a79f..54c3bbb 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -54,10 +54,10 @@ static void sync_for_device(struct msm_gem_object *msm_obj)
 
 	if (get_dma_ops(dev) && IS_ENABLED(CONFIG_ARM64)) {
 		dma_sync_sg_for_device(dev, msm_obj->sgt->sgl,
-			msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
+			msm_obj->sgt->orig_nents, DMA_BIDIRECTIONAL);
 	} else {
 		dma_map_sg(dev, msm_obj->sgt->sgl,
-			msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
+			msm_obj->sgt->orig_nents, DMA_BIDIRECTIONAL);
 	}
 }
 
@@ -67,10 +67,10 @@ static void sync_for_cpu(struct msm_gem_object *msm_obj)
 
 	if (get_dma_ops(dev) && IS_ENABLED(CONFIG_ARM64)) {
 		dma_sync_sg_for_cpu(dev, msm_obj->sgt->sgl,
-			msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
+			msm_obj->sgt->orig_nents, DMA_BIDIRECTIONAL);
 	} else {
 		dma_unmap_sg(dev, msm_obj->sgt->sgl,
-			msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
+			msm_obj->sgt->orig_nents, DMA_BIDIRECTIONAL);
 	}
 }
 
diff --git a/drivers/gpu/drm/msm/msm_iommu.c b/drivers/gpu/drm/msm/msm_iommu.c
index ad58cfe..b0ca084 100644
--- a/drivers/gpu/drm/msm/msm_iommu.c
+++ b/drivers/gpu/drm/msm/msm_iommu.c
@@ -43,7 +43,8 @@ static int msm_iommu_map(struct msm_mmu *mmu, uint64_t iova,
 	struct msm_iommu *iommu = to_msm_iommu(mmu);
 	size_t ret;
 
-	ret = iommu_map_sg(iommu->domain, iova, sgt->sgl, sgt->nents, prot);
+	ret = iommu_map_sg(iommu->domain, iova, sgt->sgl, sgt->orig_nents,
+			   prot);
 	WARN_ON(!ret);
 
 	return (ret == len) ? 0 : -EINVAL;
-- 
1.9.1