On Tue, 15 Apr 2014 22:08:45 +0900 Akinobu Mita <[email protected]> wrote:
> Calling dma_alloc_coherent() with __GFP_ZERO must return zeroed memory. > > But when the contiguous memory allocator (CMA) is enabled on x86 and > the memory region is allocated by dma_alloc_from_contiguous(), it > doesn't return zeroed memory. Because dma_generic_alloc_coherent() > forgot to fill the memory region with zero if it was allocated by > dma_alloc_from_contiguous() > > Most implementations of dma_alloc_coherent() return zeroed memory > regardless of whether __GFP_ZERO is specified. So this fixes it by > unconditionally zeroing the allocated memory region. > > Alternatively, we could fix dma_alloc_from_contiguous() to return > zeroed out memory and remove memset() from all caller of it. But we > can't simply remove the memset on arm because __dma_clear_buffer() is > used there for ensuring cache flushing and it is used in many places. > Of course we can do redundant memset in dma_alloc_from_contiguous(), > but I think this patch is less impact for fixing this problem. But this patch does a duplicated memset if the page was allocated by alloc_pages_node()? Would it not be better to pass the gfp_t to dma_alloc_from_contiguous() and have it implement __GFP_ZERO? That will fix thsi inefficiency, will be symmetrical with the other underlying allocators and should permit the appropriate fixups in arm? > --- a/arch/x86/kernel/pci-dma.c > +++ b/arch/x86/kernel/pci-dma.c > @@ -97,7 +97,6 @@ void *dma_generic_alloc_coherent(struct device *dev, size_t > size, > > dma_mask = dma_alloc_coherent_mask(dev, flag); > > - flag |= __GFP_ZERO; > again: > page = NULL; > /* CMA can be used only in the context which permits sleeping */ > @@ -120,7 +119,7 @@ again: > > return NULL; > } > - > + memset(page_address(page), 0, size); > *dma_addr = addr; > return page_address(page); > } > -- > 1.8.3.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
