MIPS64 modules

[Jayachandran C.]

On Thu, Jan 12, 2012 at 2:00 PM, Alan Cox <alc at rice.edu> wrote:
> On 01/12/2012 01:50, Jayachandran C. wrote:
>>
>> On Thu, Jan 12, 2012 at 4:51 AM, Oleksandr Tymoshenko<gonzo at freebsd.org>
>>  wrote:
>>>
>>>    Modules on MIPS use the same interface as AMD64 modules:
>>> sys/kern/link_elf_obj.c. It works for MIPS32 but there is a problem
>>> with MIPS64. sys/kern/link_elf_obj.c calls vm_map_find that uses
>>> KERNBASE as a map base. As I told - it works for mips32 because
>>> KERNBASE for mips32 is located before actual virtual memory area
>>> (KERNBASE points to directly-mapped KSEG0 segment). But for MIPS64
>>> it's not the case - KERNBASE points to the very end of address space
>>> and vm_map_find fails.
>>>
>>> Using VM_MIN_KERNEL_ADDRESS fixes this problem. So the question is -
>>> what should I do? Add #ifdef to link_elf_obj.c as in kmem_init in
>>> vm/vm_kern.c or change KERNBASE to VM_MIN_KERNEL_ADDRESS?
>>
>> This is probably the right fix for both 32 and 64-bit mips. Using a
>> KSEG0 address as argument for vm_map_find is not correct as the kernel
>> map does not include that region for mips.
>>
>> This reminds me of another issue I had seen in kern/link_elf.c, the
>> value of linker_kernel_file->address is also set to KERNBASE, but this
>> really should be KERNLOADADDR (used in our conf files) for mips.
>
> I was somewhat surprised to find that KERNBASE points to the direct map.
>  What is the virtual address range for a running kernel's code and data
> segments?  In other words, are the kernel code and data segments accessed
> through the direct map even after initialization?

Yes,  this direct map (KSEG0 in 32bit and CKSEG0 in 64bit) maps the
first 512MB physical memory and is outside the VM_MIN_KERNEL_ADDRESS -
VM_MAX_KERNEL_ADDRESS range.  KERNBASE points to the start of this
direct map.

In 64 bit, there are a few more direct maps (XKPHYS) which maps the
whole physical memory (location depends on the caching needed). We use
this when  we need a direct mapped pointer (by MIPS_PHYS_TO_DIRECT) in
64 bit. This is also outside the kernel min and max vm.

JC.