Re: how to use TLB to prevent Linux accessing a particular memory region

Re: how to use TLB to prevent Linux accessing a particular memory region

[Jim Brooks]

> Out of 32MB of DDR 8MB is reserved for use by DSP
> processor. But the MIPS processor downloads firmware
> into this reserved memory for the DSP.
>
> Now, is it possible to use the TLB to prevent Linux
> from accessing the reserved memory after the
firmware
> has been downloaded?

Well, even if you did remap PTEs (TLBs are N/A),
or claimed that special memory, that may be too late.
The kernel might've already allocated
and stomped over it.

A reliable way is to redefine the kernel's "memory
map"
which takes effect during boot.
Look for the memory map as a .h in arch/ (IIRC).

--
Jim Brooks


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com 

how to use TLB to prevent Linux accessing a particular memory region

[veerasena reddy]

Hi,

I have a board, which has two processors ( one is MIPS
on which Linux-2.6.18 kernel runs and another is DSP
based processor) and 32MB DDR.

Out of 32MB of DDR 8MB is reserved for use by DSP
processor. But the MIPS processor downloads firmware
into this reserved memory for the DSP.

Now, is it possible to use the TLB to prevent Linux
from accessing the reserved memory after the firmware
has been downloaded?

Also we'd need to remove those TLB entries if the
firmware would ever need to be reloaded to the DSP'
memory region.

What are the APIs to be used to achieve the above?


Thanks in advance.

Regards,
Veerasena.


      5, 50, 500, 5000 - Store N number of mails in your inbox. Go to http://help.yahoo.com/l/in/yahoo/mail/yahoomail/tools/tools-08.html

Re: how to use TLB to prevent Linux accessing a particular memory region

[J. Scott Kasten]

Really, it sounds more like you want a custom driver that "owns" that 
region of memory so it's marked as used and this driver is the gate 
keeper.  I wonder if the console frame buffer driver for the mips ip32 
arch might be a good example for you as it swallows a several meg chunk of 
memory for the display.

-S-

On Tue, 16 Oct 2007, veerasena reddy wrote:

> Hi,
>
> I have a board, which has two processors ( one is MIPS
> on which Linux-2.6.18 kernel runs and another is DSP
> based processor) and 32MB DDR.
>
> Out of 32MB of DDR 8MB is reserved for use by DSP
> processor. But the MIPS processor downloads firmware
> into this reserved memory for the DSP.
>
> Now, is it possible to use the TLB to prevent Linux
> from accessing the reserved memory after the firmware
> has been downloaded?
>
> Also we'd need to remove those TLB entries if the
> firmware would ever need to be reloaded to the DSP'
> memory region.
>
> What are the APIs to be used to achieve the above?
>
>
> Thanks in advance.
>
> Regards,
> Veerasena.
>
>
>      5, 50, 500, 5000 - Store N number of mails in your inbox. Go to http://help.yahoo.com/l/in/yahoo/mail/yahoomail/tools/tools-08.html
>
>

Re: how to use TLB to prevent Linux accessing a particular memory region

[linux-os (Dick Johnson)]

On Tue, 16 Oct 2007, veerasena reddy wrote:

> Hi,
>
> I have a board, which has two processors ( one is MIPS
> on which Linux-2.6.18 kernel runs and another is DSP
> based processor) and 32MB DDR.
>
> Out of 32MB of DDR 8MB is reserved for use by DSP
> processor. But the MIPS processor downloads firmware
> into this reserved memory for the DSP.
>
> Now, is it possible to use the TLB to prevent Linux
> from accessing the reserved memory after the firmware
> has been downloaded?
>
> Also we'd need to remove those TLB entries if the
> firmware would ever need to be reloaded to the DSP'
> memory region.
>
> What are the APIs to be used to achieve the above?
>
>
> Thanks in advance.
>
> Regards,
> Veerasena.
>
>
>      5, 50, 500, 5000 - Store N number of mails in your inbox. Go to http://help.yahoo.com/l/in/yahoo/mail/yahoomail/tools/tools-08.html
> -

Can't you just memory-map the area you need? That reserves it
until it's unmapped. You don't need to directly touch the TLB.
If you need a physical location, use ioremap_nocache() in your
driver. If you can't get your physical location because the
kernel already uses it, boot the kernel with mem=xxx on the
command-line to prevent the kernel from using memory you
want to reserve for your DSP. You can use num_physpages
(an integer) to find out the last page the kernel uses.

BTW, if this is a new design, most DSP devices put their
RAM on their own board so you don't have these problems.
That RAM gets mmaped to user-space as needed for access,
that address being set asside in PCI space.


Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.24 on an i686 machine (5592.59 BogoMips).
My book : http://www.AbominableFirebug.com/
_


****************************************************************
The information transmitted in this message is confidential and may be privileged.  Any review, retransmission, dissemination, or other use of this information by persons or entities other than the intended recipient is prohibited.  If you are not the intended recipient, please notify Analogic Corporation immediately - by replying to this message or by sending an email to DeliveryErrors@analogic.com - and destroy all copies of this information, including any attachments, without reading or disclosing them.

Thank you.