linux-kernel - Re: [PATCH] xen: Add __GFP_DMA flag when xen_swiotlb

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Message-ID: <5538C0D4.5050400@citrix.com>
Date:	Thu, 23 Apr 2015 10:52:20 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	<xen-devel@...ts.xensource.com>
CC:	<baozich@...il.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] xen: Add __GFP_DMA flag when xen_swiotlb_init gets free
 pages on ARM

On 23/04/15 10:47, Stefano Stabellini wrote:
> Make sure that xen_swiotlb_init allocates buffers that are DMA capable
> when at least one memblock is available below 4G. Otherwise we assume
> that all devices on the SoC can cope with >4G addresses.

This commit message must explain why the PFNs (IPAs) are relevant for DMA.

David

> No functional changes on x86.
> 
> From: Chen Baozi <baozich@...il.com>
> 
> Signed-off-by: Chen Baozi <baozich@...il.com>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> Tested-by: Chen Baozi <baozich@...il.com>
> 
> diff --git a/arch/arm/include/asm/xen/page.h b/arch/arm/include/asm/xen/page.h
> index 2f7e6ff..0b579b2 100644
> --- a/arch/arm/include/asm/xen/page.h
> +++ b/arch/arm/include/asm/xen/page.h
> @@ -110,5 +110,6 @@ static inline bool set_phys_to_machine(unsigned long pfn, unsigned long mfn)
>  bool xen_arch_need_swiotlb(struct device *dev,
>  			   unsigned long pfn,
>  			   unsigned long mfn);
> +unsigned long xen_get_swiotlb_free_pages(unsigned int order);
>  
>  #endif /* _ASM_ARM_XEN_PAGE_H */
> diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
> index 793551d..4983250 100644
> --- a/arch/arm/xen/mm.c
> +++ b/arch/arm/xen/mm.c
> @@ -4,6 +4,7 @@
>  #include <linux/gfp.h>
>  #include <linux/highmem.h>
>  #include <linux/export.h>
> +#include <linux/memblock.h>
>  #include <linux/of_address.h>
>  #include <linux/slab.h>
>  #include <linux/types.h>
> @@ -21,6 +22,20 @@
>  #include <asm/xen/hypercall.h>
>  #include <asm/xen/interface.h>
>  
> +unsigned long xen_get_swiotlb_free_pages(unsigned int order)
> +{
> +	struct memblock_region *reg;
> +	gfp_t flags = __GFP_NOWARN;
> +
> +	for_each_memblock(memory, reg) {
> +		if (reg->base < (phys_addr_t)0xffffffff) {
> +			flags |= __GFP_DMA;
> +			break;
> +		}
> +	}
> +	return __get_free_pages(flags, order);
> +}
> +
>  enum dma_cache_op {
>         DMA_UNMAP,
>         DMA_MAP,
> diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
> index 358dcd3..c44a5d5 100644
> --- a/arch/x86/include/asm/xen/page.h
> +++ b/arch/x86/include/asm/xen/page.h
> @@ -269,4 +269,9 @@ static inline bool xen_arch_need_swiotlb(struct device *dev,
>  	return false;
>  }
>  
> +static inline unsigned long xen_get_swiotlb_free_pages(unsigned int order)
> +{
> +	return __get_free_pages(__GFP_NOWARN, order);
> +}
> +
>  #endif /* _ASM_X86_XEN_PAGE_H */
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index 810ad41..4c54932 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -235,7 +235,7 @@ retry:
>  #define SLABS_PER_PAGE (1 << (PAGE_SHIFT - IO_TLB_SHIFT))
>  #define IO_TLB_MIN_SLABS ((1<<20) >> IO_TLB_SHIFT)
>  		while ((SLABS_PER_PAGE << order) > IO_TLB_MIN_SLABS) {
> -			xen_io_tlb_start = (void *)__get_free_pages(__GFP_NOWARN, order);
> +			xen_io_tlb_start = (void *)xen_get_swiotlb_free_pages(order);
>  			if (xen_io_tlb_start)
>  				break;
>  			order--;
> 

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