linux-kernel - Re: [PATCH v3] Fix dma_mapping

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Message-Id: <20081201230926Q.fujita.tomonori@lab.ntt.co.jp>
Date:	Mon, 1 Dec 2008 23:10:33 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	mingo@...e.hu
Cc:	fujita.tomonori@....ntt.co.jp, joro@...tes.org,
	tsbogend@...ha.franken.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] Fix dma_mapping_error for 32bit x86

On Mon, 1 Dec 2008 13:55:01 +0100
Ingo Molnar <mingo@...e.hu> wrote:

> 
> * FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:
> 
> > On Mon, 1 Dec 2008 12:34:51 +0100
> > Joerg Roedel <joro@...tes.org> wrote:
> > 
> > > On Sat, Nov 29, 2008 at 01:46:27PM +0100, Thomas Bogendoerfer wrote:
> > > > Devices like b44 ethernet can't dma from addresses above 1GB. The driver
> > > > handles this cases by falling back to GFP_DMA allocation. But for detecting
> > > > the problem it needs to get an indication from dma_mapping_error.
> > > > The bug is triggered by using a VMSPLIT option of 2G/2G.
> > > 
> > > Looks like your system uses swiotlb as the dma_ops backend. Its the only
> > > implementation providing the ops->mapping_error callback and does not
> > > use bad_dma_address as the error value.
> > 
> > I think that you misunderstand the problem.
> > 
> > He uses X86_32 so swiotlb should not be used (which is available on 
> > only X86_64 and IA64 for now).
> > 
> > b44 needs an address under 1GB so it sets device->dma_mask to 
> > DMA_30BIT_MASK. With VMSPLIT option of 2G/2G, I guess that b44 could 
> > get addresses above 1GB from the networking subsystem. In such case, 
> > nommu_map_single returns bad_dma_address properly, but on X86_32, 
> > dma_mapping_error always returns 0 (success). So b44 wrongly thinks 
> > that the address is under 1GB.
> > 
> > This patch fixes dma_mapping_error() to check a passed address
> > properly (compares it with bad_dma_address).
> > 
> > As I already wrote, the current git needs a patch modified slightly:
> > 
> > http://marc.info/?l=linux-kernel&m=122797163405377&w=2
> 
> i have i queued up in x86/urgent, see below.

As I wrote, just removing #ifdef is better since:

1) Xen people want swiotlb on X86_32. swiotlb uses ops->mapping_error
so X86_32 also needs to check ops->mapping_error.

2) Removing #ifdef hack is always good.


But this patch fixes the bug and it works for now. And I think that
Thomas tested it. So it's fine to commit this patch by me.

I'll send a patch to remove the ifdef on the top of this patch after
this patch goes into mainline.


> 
> -------------->
> From 7b1dedca42ac0d0d0be01e39d8461bb53a2389b3 Mon Sep 17 00:00:00 2001
> From: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> Date: Sat, 29 Nov 2008 13:46:27 +0100
> Subject: [PATCH] x86: fix dma_mapping_error for 32bit x86
> 
> Devices like b44 ethernet can't dma from addresses above 1GB. The driver
> handles this cases by falling back to GFP_DMA allocation. But for detecting
> the problem it needs to get an indication from dma_mapping_error.
> The bug is triggered by using a VMSPLIT option of 2G/2G.
> 
> Signed-off-by: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> Acked-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
> Signed-off-by: Ingo Molnar <mingo@...e.hu>
> ---
>  arch/x86/include/asm/dma-mapping.h |    6 ++----
>  1 files changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/dma-mapping.h b/arch/x86/include/asm/dma-mapping.h
> index 7f225a4..097794f 100644
> --- a/arch/x86/include/asm/dma-mapping.h
> +++ b/arch/x86/include/asm/dma-mapping.h
> @@ -71,15 +71,13 @@ static inline struct dma_mapping_ops *get_dma_ops(struct device *dev)
>  /* Make sure we keep the same behaviour */
>  static inline int dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
>  {
> -#ifdef CONFIG_X86_32
> -	return 0;
> -#else
> +#ifdef CONFIG_X86_64
>  	struct dma_mapping_ops *ops = get_dma_ops(dev);
>  	if (ops->mapping_error)
>  		return ops->mapping_error(dev, dma_addr);
>  
> -	return (dma_addr == bad_dma_address);
>  #endif
> +	return (dma_addr == bad_dma_address);
>  }
>  
>  #define dma_alloc_noncoherent(d, s, h, f) dma_alloc_coherent(d, s, h, f)
> --
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