Messages in this thread | | | Subject | Re: [PATCH] drm/vmwgfx: Fix scatterlist unmapping | From | Thomas Hellstrom <> | Date | Wed, 25 Apr 2018 15:21:19 +0200 |
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Hi, Robin,
Thanks for the patch. It was some time since I put together that code, but I remember hitting something similar to
https://www.linuxquestions.org/questions/linux-kernel-70/%27nents%27-argument-of-dma_unmap_sg-4175621964/
Even if it's clear from the documentation that orig_nents should be used.
/Thomas
On 04/13/2018 05:14 PM, Robin Murphy wrote: > dma_unmap_sg() should be called with the same number of entries > originally passed to dma_map_sg(), not the number it returned, which may > be fewer. Admittedly this driver probably never runs on non-coherent > architectures where getting that wrong could lead to data loss, but it's > always good to be correct, and it's trivially easy to fix by just > restoring the SG table state before the call instead of afterwards. > > Signed-off-by: Robin Murphy <robin.murphy@arm.com> > --- > > Found by inspection while poking around TTM users. > > drivers/gpu/drm/vmwgfx/vmwgfx_buffer.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_buffer.c b/drivers/gpu/drm/vmwgfx/vmwgfx_buffer.c > index 21111fd091f9..971223d39469 100644 > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_buffer.c > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_buffer.c > @@ -369,9 +369,9 @@ static void vmw_ttm_unmap_from_dma(struct vmw_ttm_tt *vmw_tt) > { > struct device *dev = vmw_tt->dev_priv->dev->dev; > > + vmw_tt->sgt.nents = vmw_tt->sgt.orig_nents; > dma_unmap_sg(dev, vmw_tt->sgt.sgl, vmw_tt->sgt.nents, > DMA_BIDIRECTIONAL); > - vmw_tt->sgt.nents = vmw_tt->sgt.orig_nents; > } > > /**
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