linux-kernel - Re: [PATCH 1/2] x86 swiotlb: Verify we can perform the remapping requested.

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Date:	Thu, 20 Oct 2011 20:40:31 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	fujita.tomonori@....ntt.co.jp
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86 swiotlb: Verify we can perform the remapping
 requested.

On Mon, Oct 17, 2011 at 02:19:18PM -0700, Eric W. Biederman wrote:
> 
> Recently I had a driver try with a peculiar 2G dma memory limit.
> It failed in weird and strange ways because my bounce buffers were
> being allocated above 2G where the driver could not reach, and
> no error was reported when the mappings were setup.

OK, so the overflow buffer was used instead.. which presumarily
also was allocated above the 2G? That seems to point that
alloc_bootmem_low_pages is not doing its job?

> 
> Use the swiotlb_dma_supported to avoid silent problems like this
> in the future.

Which driver was it that had this limit?

> 
> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>

I also CC-ed Fujita on this as he is the swiotlb maintainer.

> ---
>  arch/x86/kernel/pci-swiotlb.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kernel/pci-swiotlb.c b/arch/x86/kernel/pci-swiotlb.c
> index 8f972cb..6a802fa 100644
> --- a/arch/x86/kernel/pci-swiotlb.c
> +++ b/arch/x86/kernel/pci-swiotlb.c
> @@ -38,7 +38,7 @@ static struct dma_map_ops swiotlb_dma_ops = {
>  	.unmap_sg = swiotlb_unmap_sg_attrs,
>  	.map_page = swiotlb_map_page,
>  	.unmap_page = swiotlb_unmap_page,
> -	.dma_supported = NULL,
> +	.dma_supported = swiotlb_dma_supported,
>  };
>  
>  /*
> -- 
> 1.7.2.5
> 
> --
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