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.
