Changing virtual adress space layout

[Devesh Rai]

Hi Mark,

Actually I want to map large portion of RAM in kernel virtual address space.
To achieve this in Linux, I did following

1) boot kernel with 256M by setting CONFIG_CMDLINE="mem=256M". This freed up more than 1GB of RAM for my module usages
2) increase KVA to 3GB by setting CONFIG_VMSPLIT_1G=y ( 1G for user and 3GB for kernel)
3) ioremap unused RAM ( 2GB - 256MB ) into Kernel virtual address space.

Changing KERNBASE and KERNVIRTADDR "makeoption" from 0xc0000000 to 0x80000000 did not worked for me. Kernel hang while loading. 

Thanks & Regards
Devesh
 
-----Original Message-----
From: Mark Tinguely [mailto:marktinguely at gmail.com] 
Sent: Thursday, January 13, 2011 10:00 PM
To: freebsd-arm at freebsd.org
Cc: Devesh Rai
Subject: Re: Changing virtual adress space layout

On 1/13/2011 1:30 AM, Devesh Rai wrote:
> Hi,
>
> I am new to FreeBSD. Can some tell how to change virtual address space layout in FreeBSD for arm?
> For x86, KVA_PAGES=N option is there in FreeBSD.  In Linux, I used CONFIG_VMSPLIT option.
> I am looking corresponding option for arm.
>
> Regards
> Devesh

I assume you have run out of space for the device virtual addresses.

KERNBASE is hard coded in sys/arm/include/vm_param.h to be 0xc0000000.

There is a related variable for each device configuration: the  
KERNVIRTADDR  "option" and "makeoption" values. This is usually in one 
of the "std" file  file for the device. KERNVIRTADDR sets the starting 
location of the executable and is sometimes different than KERNBASE.

The arm code does not map the from KERNBASE to 0xffff_ffff into the KVA. 
Instead, there is a variable that determines the maximum size of the 
kernel executable and kernel virtual address area. Above this defined 
area lies the no-cache remap memory region, device map area, high 
vector, etc.

On a tangent note: There will be a great advantage in ARMv6/ARMv7 to go 
to a 2GB UVA / 2GB KVA.

--Mark.