Chris Wright wrote:
>* Zachary Amsden (zach@xxxxxxxxxx) wrote:
>
>
>>Allow compile time creation of a hole at the high end of linear address space.
>>This makes accomodating a hypervisor a much more tractable problem by giving
>>it ample playground to live in. Currently, the hole size is fixed at config
>>time; I have experimented with dynamically sized holes, and have a later
>>patch that developes this potential, but it becomes much more useful once
>>the exact negotiation of linear address space with the hypervisor is defined.
>>
>>The fixed compile time solution is sufficient for now.
>>
>>
>
>Xen moves __FIXADDR_TOP like this:
>
>#ifdef CONFIG_X86_PAE
># define HYPERVISOR_VIRT_START (0xF5800000UL)
>#else
># define HYPERVISOR_VIRT_START (0xFC000000UL)
>#endif
>
>and
>
>#define __FIXADDR_TOP (HYPERVISOR_VIRT_START - 2 * PAGE_SIZE)
>
>and also adds bits to fixmap.
>
>So this proposed mechanism isn't quite good enough.
>
>
Hmm. I was thinking it would be compile time variable with defaults -- like
config MEMORY_HOLE
int "Create hole at top of memory (0-512 MB)"
range 0 512
default "0"
default 168 if (CONFIG_X86_PAE && CONFIG_X86_HYPERVISOR)
default 64 if (!CONFIG_X86_PAE && CONFIG_X86_HYPERVISOR)
help
Useful for creating a hole in the top of memory when running
inside of a virtual machine monitor.
Adding things to the fixmap is a separate concept, thus a separate patch ;)
Zach
