Messages in this thread | | | Subject | Re: [PATCH 1/1] arm64/dma-mapping: remove an unnecessary conversion | From | "Leizhen (ThunderTown)" <> | Date | Fri, 18 Mar 2016 09:17:08 +0800 |
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On 2016/3/17 19:59, Catalin Marinas wrote: > On Thu, Mar 17, 2016 at 07:06:27PM +0800, Leizhen (ThunderTown) wrote: >> On 2016/3/16 9:56, Leizhen (ThunderTown) wrote: >>> On 2016/3/15 23:37, Catalin Marinas wrote: >>>> On Tue, Mar 15, 2016 at 10:12:11AM +0800, Zhen Lei wrote: >>>>> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c >>>>> index a6e757c..b2f2834 100644 >>>>> --- a/arch/arm64/mm/dma-mapping.c >>>>> +++ b/arch/arm64/mm/dma-mapping.c >>>>> @@ -187,8 +187,6 @@ static void __dma_free(struct device *dev, size_t size, >>>>> void *vaddr, dma_addr_t dma_handle, >>>>> struct dma_attrs *attrs) >>>>> { >>>>> - void *swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle)); >>>>> - >>>>> size = PAGE_ALIGN(size); >>>>> >>>>> if (!is_device_dma_coherent(dev)) { >>>>> @@ -196,7 +194,7 @@ static void __dma_free(struct device *dev, size_t size, >>>>> return; >>>>> vunmap(vaddr); >>>>> } >>>>> - __dma_free_coherent(dev, size, swiotlb_addr, dma_handle, attrs); >>>>> + __dma_free_coherent(dev, size, vaddr, dma_handle, attrs); >>>>> } >>>> >>>> What happens when !is_device_dma_coherent(dev)? (hint: read two lines >>>> above __dma_free_coherent). >> >> Do you afraid "vaddr" maybe modified by these statement? >> First, it could not be __free_from_pool. Otherwise, the function >> vunmap(which after it) can not work well. Then, it count not be vunmap >> too, the parameter is defined as "const void *". >> >> In the call chain: >> __dma_free_coherent-->__dma_free_coherent-->swiotlb_free_coherent, >> only swiotlb_free_coherent finally use "vaddr". > > Exactly. So you give swiotlb_free_coherent a vaddr which has been > unmapped. It doesn't even matter whether it's still mapped since this > address is passed further to free_pages() which performs a > virt_to_page(). The latter is *only* valid on linear map addresses (and > you would actually hit the VM_BUG_ON in free_pages; you can try running > this with CONFIG_DEBUG_VM enabled and non-coherent DMA). > > For non-coherent DMA, the vaddr is not part of the linear mapping as it > has been remapped by __dma_alloc() via dma_common_contiguous_remap(), > hence for swiotlb freeing we need the actual linear map address (the > original "ptr" in __dma_alloc()). We can generate it by a > phys_to_virt(dma_to_phys(dma_handle)). >
OK, I got it.
So actually I should move the statement into branch "if (!is_device_dma_coherent(dev))", I will prepare v2.
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