Re: [PATCH] dma-mapping: don't clear GFP_ZERO in dma_alloc_attrs

Evgeniy Didin
2018-03-28T15:12:53Z

Adding linux-snps and linux-arch mailing lists.

> Revert the clearing of __GFP_ZERO in dma_alloc_attrs and move it to
> dma_direct_alloc for now.  While most common architectures always zero dma
> cohereny allocations (and x86 did so since day one) this is not documented
> and at least arc and s390 do not zero without the explicit __GFP_ZERO
> argument.
This patch fixed Ethernet issues on ARC HSDK.
https://www.spinics.net/lists/kernel/msg2762054.html

Tested-by: Evgeniy Didin <Evgeniy.Didin@synopsys.com>
> Fixes: 57bf5a8963f8 ("dma-mapping: clear harmful GFP_* flags in common code")
> Reported-by: Evgeniy Didin <Evgeniy.Didin@synopsys.com>
> Reported-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  include/linux/dma-mapping.h | 8 ++------
>  lib/dma-direct.c            | 3 +++
>  2 files changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index eb9eab4ecd6d..12fedcba9a9a 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -518,12 +518,8 @@ static inline void *dma_alloc_attrs(struct device *dev, size_t size,
>   if (dma_alloc_from_dev_coherent(dev, size, dma_handle, &cpu_addr))
>   return cpu_addr;
>
> - /*
> -  * Let the implementation decide on the zone to allocate from, and
> -  * decide on the way of zeroing the memory given that the memory
> -  * returned should always be zeroed.
> -  */
> - flag &= ~(__GFP_DMA | __GFP_DMA32 | __GFP_HIGHMEM | __GFP_ZERO);
> + /* let the implementation decide on the zone to allocate from: */
> + flag &= ~(__GFP_DMA | __GFP_DMA32 | __GFP_HIGHMEM);
>
>   if (!arch_dma_alloc_attrs(&dev, &flag))
>   return NULL;
> diff --git a/lib/dma-direct.c b/lib/dma-direct.c
> index 1277d293d4da..c0bba30fef0a 100644
> --- a/lib/dma-direct.c
> +++ b/lib/dma-direct.c
> @@ -59,6 +59,9 @@ void *dma_direct_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
>   struct page *page = NULL;
>   void *ret;
>
> + /* we always manually zero the memory once we are done: */
> + gfp &= ~__GFP_ZERO;
> +
>   /* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */
>   if (dev->coherent_dma_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS))
>   gfp |= GFP_DMA;