Re: Cache-inhibited region for certain exception handler(e500 chips, 2.4 kernel)?

[Kumar Gala <galak@kernel.crashing.org>]

On Wed, 15 Feb 2006, Xianghua Xiao wrote:

> Is there a way to put certain exception handler(e.g. machine check) on e500
> to a cache-inhibited region? 
>  
> 1. The e500 kernel puts exception handlers at the starting of the physical
> memory.
> 2. All the physical memory are covered by a few TLB1s to do
> 0xc0000000-0x00000000 translation.
> 3. We can not add a new TLB1 to map a small piece of memory, because it has
> boundary limitation(4K...256M). We can not use two TLB1 to overlap since it
> will cause program error.
> 4. When we tried to move a handler(e.g. machine check) to a different
> location, the kernel won't boot.
> 5. We don't want to map all the exceptional handlers to be cache inhibited,
> say, the first 1MB, the performance will be horrible if we do so.
>  
> Is there a way at all to tweak things like this, i.e., put an exception
> handler into a piece of memory that is cache-inhibited?
>  
> I also thought about use mlock/mmap on /dev/mem, move the specific exception
> handler to a high address then use a separate TLB1 to cover it(need change
> link script?),etc. 
>  

Why exactly do you the mcheck handler to be cache inhibited?  One simple 
way would be to setup a temp mapping in kernel virtual address space 
somewhere and have the first thing the current handler does is jump to 
that location.

- kumar