Increasing KVM on amd64

[Kostik Belousov]

On Sun, Jun 08, 2008 at 12:39:43AM -0500, Alan Cox wrote:
> Kostik Belousov wrote:
> 
> >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.
> >
> > 
> >
> 
> The change to link_elf_obj.c is supposed to ensure allocation of an 
> address in the upper 2GB of the kernel map for the module.

Ah, I overlooked it, sorry.
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