Content-class: urn:content-classes:message
MIME-Version: 1.0
Content-Type: text/plain;
	charset="us-ascii"
Content-Transfer-Encoding: 8BIT
Subject: RE: mmap/munmap on linux-2.6.11
Date: Mon, 28 Mar 2005 09:35:49 -0800
Message-ID: <5F106036E3D97448B673ED7AA8B2B6B301CD4D3A@scl-exch2k.phoenix.com>
Thread-Topic: mmap/munmap on linux-2.6.11
Thread-Index: AcUxgKd2vzo1kzJiSoG3ZJBst1M3CACO7B/A
From: "Aleksey Gorelov" <Aleksey_Gorelov@Phoenix.com>
To: <linux-os@analogic.com>, "Linux kernel" <linux-kernel@vger.kernel.org>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1486
Lines: 35

 >-----Original Message-----
>From: linux-kernel-owner@vger.kernel.org 
>[mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of linux-os
>Sent: Friday, March 25, 2005 1:19 PM
>To: Linux kernel
>Subject: mmap/munmap on linux-2.6.11
>
>Memory gurus,
>
>We have an application where a driver allocates DMA-able memory.
>This DMA-able memory is mmap()ed to user-space. To conserve
>DMA memory only single pages are obtained using
>  __get_dma_pages(GFP_KERNEL, 1) (one page at a time). These
>pages, that may be scattered all about, are mmap()ed into contiguous
>user data-space. The DMA engine uses a scatter-list so we can
>write DMA pages anywhere. They don't have to be contiguous.
>
>Here's a catch. It would be nice to release those DMA pages
>when we don't need them. However, there doesn't appear to
>be any way for driver code to know when munmap() has been
>called and those DMA pages are available to be released.
>
>How do I know that munmap() has been called? It turns out
>that if I release those pages before unmapping the user-mode,
>the system will crash. Therefore this could be a DOS attack
>if my driver ever allowed the DMA pages to be released.

munmap() should do the job for you and release those automatically.

Aleks.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/