Subject: Re: [PATCH 18 of 38] x86: unify pci iommu setup and allow swiotlb
	to	compile for 32 bit
From: Ian Campbell <Ian.Campbell@citrix.com>
To: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: jeremy@goop.org, mingo@elte.hu, linux-kernel@vger.kernel.org,
       xen-devel@lists.xensource.com, x86@kernel.org
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Organization: Citrix Systems, Inc.
Date: Wed, 26 Nov 2008 09:36:49 +0000
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On Wed, 2008-11-26 at 11:53 +0900, FUJITA Tomonori wrote:
> 
> > +     BUG_ON(max_slots > 1UL << (BITS_PER_LONG - IO_TLB_SHIFT));
> 
> How can this BUG_ON happen? Using u64 for the mask is fine though.

It covers the cases where the previous code would have overflowed. It
can't happen right now because although mask is 64 bits the value
assigned to it is currently sizeof(unsigned long). If someone changes
the type of that field then we would start seeing unexpected values.

Ian.

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