Calling function from address

[Peter Teoh]

http://infocenter.arm.com/help/topic/com.arm.doc.dui0056d/ch07s05s01.html

this provide the additional info that cache store virtual addresses,
and since different processes may have same virtual address, but
different physical address, u have to beware!

On Sat, Jun 11, 2011 at 2:45 PM, Peter Teoh <htmldeveloper at gmail.com> wrote:
> For ARM, MMU info can be found here:
>
> http://infocenter.arm.com/help/topic/com.arm.doc.ddi0333h/Babbhigi.html
>
> That is the theory behind MMU in ARM....but if u want the high level API, look
>  under the arch/arm/mm directory lots of examples there.   Otherwise u
> might try the following steps as proposed by "Marco Wang" - google for
> it.   To quote:
>
> phys_to_virt() only works with directly mapped physical address. I
> don't think using phys_to_virt() is the best idea, anyway. Usually you
> do this in several steps in a device driver:
>
> 1. Call request_mem_region() to request virtual memory region;
> 2. Call ioremap() to map physical address to virtual address;
> 3. Read/write mapped virtual address by using iowriteXX() /
> ioreadXX(), etc. Here XX can be 8, 16, or 32 for example, represents
> bit width.
> 4. Call iounmap() and release_mem_region() to release memory mapping;
>
> Thanks,
> Marco Wang
>
> On Fri, Jun 10, 2011 at 3:46 PM, Micha M. <kernelnewbies at mail.i88.de> wrote:
>> On Fri, Jun 10, 2011 at 07:30:46AM +0800, Gavin Guo wrote:
>>> > So maybe I have to explain some more. There is some code located in the
>>> > pysical address space and I need to call it from a kernel module. The
>>> > problem is, that the code must be run from that location it is stored (it
>>> > contains absolute jumps). So I'd like to be able to run that code in that
>>> > address space, or to "tell" the keeernel to ignore page faults/memory
>>> > protection on a certain address range, so that I can jump there run the
>>> > code and return to the caller (kernel module)
>>>
>>> What is the architecture do you use? ex: x86, arm, mips,...
>>
>> ARM.
>>
>>> I know in some platform like andes, it is possible to turn off the
>>> virtual memory.
>>> Then you can jump to the physical address. After doing what you want, turning on
>>> virtual memory again. Finally, system return to the normal operation.
>>> However, the
>>> code is a little tricky. Before turning off the virtual memory, you
>>> must lock the
>>> code jumping to physical address in cache. Otherwise, behaviors, after
>>> turning off
>>> the cache, is unpredictable.
>>>
>>> Gavin Guo
>>
>
>
> --
> Regards,
> Peter Teoh
>



-- 
Regards,
Peter Teoh