Increasing KVM on amd64

[Kostik Belousov]

On Sat, Jun 07, 2008 at 06:59:35PM -0500, Alan Cox wrote:
> You can download a patch from 
> http://www.cs.rice.edu/~alc/amd64_kvm_6GB.patch that increases amd64's 
> kernel virtual address space to 6GB.  This patch also increases the 
> default for the kmem map to almost 2GB.  I believe that kernel loadable 
> modules still work.  However, I suspect that mini-dumps are broken.
The amd64 modules text/data/bss virtual addresses are allocated from the 
kernel_map (link_elf_obj.c, link_elf_load_file). Now, the lower end
of the kernel_map is top-6Gb.

Kernel code (both kernel proper and modules) is compiled for "kernel memory
model", according to the gcc info:
`-mcmodel=kernel'
Generate code for the kernel code model.  The kernel runs in the
negative 2 GB of the address space.  This model has to be used for
Linux kernel code.

I suspect we have a problem there.

> 
> I don't plan on committing this patch in its current form.  Some of the 
> changes are done in a hackish way.  I am, however, curious to hear 
> whether or not it works for you.
> 
> Alan
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