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SubjectRe: [PATCH 5/5] Create a hole in high linear address space
Chris Wright wrote:

>* Zachary Amsden ( 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)
># define HYPERVISOR_VIRT_START (0xFC000000UL)
>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

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)
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 ;)

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