Re: [patch] i386, vdso=[0|1] boot option and/proc/sys/vm/vdso_enabled

From: Andrew Morton
Date: Sun May 21 2006 - 05:52:17 EST

Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote:
> Hypervisors want to use memory at the top of the address space
> (eg. 64MB for Xen, or 168MB for Xen w/ PAE). Creating this hole means
> moving the vsyscall page away from 0xffffe000.
> If we create this hole statically with a config option, we give up,
> say, 256MB of lowmem for the case where a hypervisor-capable kernel is
> actually running on native hardware.
> If we create this hole dynamically and leave the vsyscall page at the
> top of kernel memory, we would have to patch up the vsyscall elf
> header at boot time to reflect where we put it.
> Instead, this patch moves the vsyscall page into the user address
> region, just below PAGE_OFFSET: it's still at a fixed address, but
> it's not where the hypervisor wants to be, so resizing the hole is
> trivial.

Seems to work.
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