linux-kernel - Re: Mapping non-page aligned data to user

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Message-ID: <242952.40744.qm@web33401.mail.mud.yahoo.com>
Date:	Thu, 5 Feb 2009 18:29:11 -0800 (PST)
From:	Vira <sri1369_s@...oo.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: Mapping non-page aligned data to user

I am trying to map DMAed packets directly to contiguous user buffer (avoiding the copy)- thinking of how to skip the packet headers here.

Thx,
-- vira

--- On Thu, 2/5/09, Robert Hancock <hancockrwd@...il.com> wrote:

> From: Robert Hancock <hancockrwd@...il.com>
> Subject: Re: Mapping non-page aligned data to user
> To: linux-kernel@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Date: Thursday, February 5, 2009, 4:27 PM
> Vira wrote:
> > Hi, 
> > Is there a way to map a non-page aligned kernel
> physical address to user virtual address? remap_pfn_range
> and vm_insert_page operate only on page-aligned physical
> addresses.
> > 
> > If there is no such support, would it be too
> complicated to try out
> > writing something on my own to map non-page aligned
> addresses (the data
> > size is under my control - so I can make that a
> multiple of page size)?
> > 
> > Any suggestions appreciated.
> 
> The CPU, and therefore the kernel, couldn't ensure that
> the user doesn't write outside the mapped region of
> kernel memory if it's not page aligned (the access
> control is page granularity only). That seems like it would
> be a show-stopper in most cases.
> 
> What exactly is it you're trying to achieve with this?
> 
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