Hi Sasha,

It's probably best *not* to backport this patch.. drm/msm abuses the DMA API in a way that it is not intended be used, to work around the lack of cache sync API exported to kernel modules on arm/arm64. I couldn't really guarantee that this patch does the right thing on older versions of DMA API, so best to leave things as they were.

BR, -R

On Fri, Aug 2, 2019 at 6:21 AM Sasha Levin sashal@kernel.org wrote:

From: Rob Clark robdclark@chromium.org

[ Upstream commit 0036bc73ccbe7e600a3468bf8e8879b122252274 ]

Recently splats like this started showing up:

WARNING: CPU: 4 PID: 251 at drivers/iommu/dma-iommu.c:451 __iommu_dma_unmap+0xb8/0xc0 Modules linked in: ath10k_snoc ath10k_core fuse msm ath mac80211 uvcvideo cfg80211 videobuf2_vmalloc videobuf2_memops vide CPU: 4 PID: 251 Comm: kworker/u16:4 Tainted: G W 5.2.0-rc5-next-20190619+ #2317 Hardware name: LENOVO 81JL/LNVNB161216, BIOS 9UCN23WW(V1.06) 10/25/2018 Workqueue: msm msm_gem_free_work [msm] pstate: 80c00005 (Nzcv daif +PAN +UAO) pc : __iommu_dma_unmap+0xb8/0xc0 lr : __iommu_dma_unmap+0x54/0xc0 sp : ffff0000119abce0 x29: ffff0000119abce0 x28: 0000000000000000 x27: ffff8001f9946648 x26: ffff8001ec271068 x25: 0000000000000000 x24: ffff8001ea3580a8 x23: ffff8001f95ba010 x22: ffff80018e83ba88 x21: ffff8001e548f000 x20: fffffffffffff000 x19: 0000000000001000 x18: 00000000c00001fe x17: 0000000000000000 x16: 0000000000000000 x15: ffff000015b70068 x14: 0000000000000005 x13: 0003142cc1be1768 x12: 0000000000000001 x11: ffff8001f6de9100 x10: 0000000000000009 x9 : ffff000015b78000 x8 : 0000000000000000 x7 : 0000000000000001 x6 : fffffffffffff000 x5 : 0000000000000fff x4 : ffff00001065dbc8 x3 : 000000000000000d x2 : 0000000000001000 x1 : fffffffffffff000 x0 : 0000000000000000 Call trace: __iommu_dma_unmap+0xb8/0xc0 iommu_dma_unmap_sg+0x98/0xb8 put_pages+0x5c/0xf0 [msm] msm_gem_free_work+0x10c/0x150 [msm] process_one_work+0x1e0/0x330 worker_thread+0x40/0x438 kthread+0x12c/0x130 ret_from_fork+0x10/0x18 ---[ end trace afc0dc5ab81a06bf ]---

Not quite sure what triggered that, but we really shouldn't be abusing dma_{map,unmap}_sg() for cache maint.

Cc: Stephen Boyd sboyd@kernel.org Tested-by: Stephen Boyd swboyd@chromium.org Reviewed-by: Jordan Crouse jcrouse@codeaurora.org Signed-off-by: Rob Clark robdclark@chromium.org Signed-off-by: Sean Paul seanpaul@chromium.org Link: https://patchwork.freedesktop.org/patch/msgid/20190630124735.27786-1-robdcla... Signed-off-by: Sasha Levin sashal@kernel.org

---

drivers/gpu/drm/msm/msm_gem.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c index 49a019939ccdc..a3b5fe1a13944 100644 --- a/drivers/gpu/drm/msm/msm_gem.c +++ b/drivers/gpu/drm/msm/msm_gem.c @@ -97,7 +97,7 @@ static struct page **get_pages(struct drm_gem_object *obj) * because display controller, GPU, etc. are not coherent: */ if (msm_obj->flags & (MSM_BO_WC|MSM_BO_UNCACHED))

•                   dma_map_sg(dev->dev, msm_obj->sgt->sgl,
  

•                   dma_sync_sg_for_device(dev->dev, msm_obj->sgt->sgl,
                                    msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
    }
  
  

@@ -127,7 +127,7 @@ static void put_pages(struct drm_gem_object *obj) * GPU, etc. are not coherent: */ if (msm_obj->flags & (MSM_BO_WC|MSM_BO_UNCACHED))

•                           dma_unmap_sg(obj->dev->dev, msm_obj->sgt->sgl,
  

•                           dma_sync_sg_for_cpu(obj->dev->dev, msm_obj->sgt->sgl,
                                         msm_obj->sgt->nents,
                                         DMA_BIDIRECTIONAL);
  
  

-- 2.20.1