Re: [RFC PATCH 09/35] Change __FIXADDR_TOP to leave room for the hypervisor.

Anthony Liguori
2006-03-22T17:28:16Z

Chris Wright wrote:
> Move the definition of __FIXADDR_TOP into a subarch include file so
> that it can be overridden for subarch xen -- the hypervisor needs
> about 64MB at the top of the address space.
>

I think this is more generally useful if it's actually a CONFIG option
(as it was in the VMI patches) instead of subarch specific. Qemu has
had a "fast" patch for a while that pretty much just increases the size
of the memory hole and changes ___PAGE_OFFSET to be lower in memory.
There are a number of interesting things one can do once there's an
adequately sized hole too (assuming you're doing full-virtualization).

Regards,

Anthony Liguori

> Signed-off-by: Ian Pratt <ian.pratt@xensource.com>
> Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
> Signed-off-by: Chris Wright <chrisw@sous-sol.org>
> ---
> include/asm-i386/fixmap.h | 8 +-------
> include/asm-i386/mach-default/mach_fixmap.h | 11 +++++++++++
> include/asm-i386/mach-xen/mach_fixmap.h | 11 +++++++++++
> 3 files changed, 23 insertions(+), 7 deletions(-)
>
> --- xen-subarch-2.6.orig/include/asm-i386/fixmap.h
> +++ xen-subarch-2.6/include/asm-i386/fixmap.h
> @@ -14,13 +14,7 @@
> #define _ASM_FIXMAP_H
>
> #include <linux/config.h>
> -
> -/* used by vmalloc.c, vsyscall.lds.S.
> - *
> - * Leave one empty page between vmalloc'ed areas and
> - * the start of the fixmap.
> - */
> -#define __FIXADDR_TOP 0xfffff000
> +#include <mach_fixmap.h>
>
> #ifndef __ASSEMBLY__
> #include <linux/kernel.h>
> --- /dev/null
> +++ xen-subarch-2.6/include/asm-i386/mach-default/mach_fixmap.h
> @@ -0,0 +1,11 @@
> +#ifndef __ASM_MACH_FIXMAP_H
> +#define __ASM_MACH_FIXMAP_H
> +
> +/* used by vmalloc.c, vsyscall.lds.S.
> + *
> + * Leave one empty page between vmalloc'ed areas and
> + * the start of the fixmap.
> + */
> +#define __FIXADDR_TOP 0xfffff000
> +
> +#endif /* __ASM_MACH_FIXMAP_H */
> --- /dev/null
> +++ xen-subarch-2.6/include/asm-i386/mach-xen/mach_fixmap.h
> @@ -0,0 +1,11 @@
> +#ifndef __ASM_MACH_FIXMAP_H
> +#define __ASM_MACH_FIXMAP_H
> +
> +/* used by vmalloc.c, vsyscall.lds.S.
> + *
> + * Leave one empty page between vmalloc'ed areas and
> + * the start of the fixmap.
> + */
> +#define __FIXADDR_TOP (HYPERVISOR_VIRT_START - 2 * PAGE_SIZE)
> +
> +#endif /* __ASM_MACH_FIXMAP_H */
>
> --
>
> ------------------------------------------------------------------------
>
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