linux-kernel - RE: [PATCH 1/4] add is_buffer_dma

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Date:	Wed, 10 Sep 2008 01:49:37 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	tony.luck@...el.com
Cc:	fujita.tomonori@....ntt.co.jp, mingo@...hat.com,
	linux-kernel@...r.kernel.org, joerg.roedel@....com
Subject: RE: [PATCH 1/4] add is_buffer_dma_capable helper function

On Tue, 9 Sep 2008 09:17:05 -0700
"Luck, Tony" <tony.luck@...el.com> wrote:

> +static inline int is_buffer_dma_capable(u64 mask, dma_addr_t addr, size_t size)
> +{
> +       return addr + size <= mask;
> +}
> 
> Do we care about wrap-around (e.g. addr=0xffffffffffffffff size=2)?

We could do something like:

      return addr < mask && addr + size <= mask;


But such wrap-around can happen only with a buggy IOMMU
implementation. A driver will does DMA from 0xffffffffffffffff to
0x1. Even if this function does the right thing in such case, we will
be dead?
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