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Re: Support for physical memory above 0x20000000

To: Kevin Paul Herbert <kph@ayrnetworks.com>
Subject: Re: Support for physical memory above 0x20000000
From: Ralf Baechle <ralf@oss.sgi.com>
Date: Tue, 8 Jan 2002 20:21:19 -0200
Cc: linux-mips@oss.sgi.com
In-reply-to: <a05100303b860f1fff2dd@[192.168.1.5]>; from kph@ayrnetworks.com on Tue, Jan 08, 2002 at 11:07:53AM -0800
References: <a05100303b860f1fff2dd@[192.168.1.5]>
Sender: owner-linux-mips@oss.sgi.com
User-agent: Mutt/1.2.5i
On Tue, Jan 08, 2002 at 11:07:53AM -0800, Kevin Paul Herbert wrote:

> I'm working with a somewhat dated kernel (2.4.2+patches) and have 
> discovered that there are problems with physical memory that does not 
> map into KSEG0/KSEG1. I looked over the list archives (manually, I 
> couldn't find a search interface) and it appears that this is still 
> the case for current kernels (at least as of a note from last summer, 
> the last time the issue seems to have come up.)
> 
> Obviously, phys_to_virt() is going to be a problem but besides this 
> I'm wondering what anybody may have done to support physical memory 
> that is not always mapped into the virtual address space, so that I 
> don't have to reinvent the wheel.
> 
> When I tell the kernel about the memory above 0x20000000, userland 
> fails to start; the kernel gets as far as execve()'ing init, but 
> nothing happens (interrupts are enabled; I get echo on the console, 
> but nothing from userland).

Correct.  There are two ways to solve this problem.  For the 32-bit kernel
I've got a highmem patch and the 64-bit kernel memory limits are the
hardware's memory limits.  I'll post the highmem patch soon.  I was
planning to have it ready by now but a flu sent me to bed instead ...

  Ralf

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