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[Xen-devel] [PATCH 8 of 13] Add a bootparameter to reserve high linear a

To: Andrew Morton <akpm@xxxxxxxx>
Subject: [Xen-devel] [PATCH 8 of 13] Add a bootparameter to reserve high linear address space for hypervisors
From: Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>
Date: Tue, 01 Aug 2006 13:00:46 -0700
Cc: Virtualization <virtualization@xxxxxxxx>, Zachary Amsden <zach@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>, Hollis Blanchard <hollisb@xxxxxxxxxx>, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, Linux Kernel <linux-kernel@xxxxxxxxxxxxxxx>, Chris Wright <chrisw@xxxxxxxxxxxx>, Ian Pratt <ian.pratt@xxxxxxxxxxxxx>, "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>, Gerd Hoffmann <kraxel@xxxxxxx>, Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>, Christoph Lameter <clameter@xxxxxxx>
Delivery-date: Tue, 01 Aug 2006 13:24:04 -0700
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1 file changed, 13 insertions(+)
arch/i386/kernel/setup.c |   13 +++++++++++++

This is necessary to allow dynamically loaded hypervisor modules, which
might not happen until userspace is already running, and also provides a
useful tool to benchmark the performance impact of reduced lowmem address

Signed-off-by: Zachary Amsden <zach@xxxxxxxxxx>


diff -r b6c100bb5ca5 -r 0adfc39039c7 arch/i386/kernel/setup.c
--- a/arch/i386/kernel/setup.c  Tue Aug 01 01:32:00 2006 -0700
+++ b/arch/i386/kernel/setup.c  Tue Aug 01 01:32:00 2006 -0700
@@ -917,6 +917,19 @@ static void __init parse_cmdline_early (
                else if (!memcmp(from, "vmalloc=", 8))
                        __VMALLOC_RESERVE = memparse(from+8, &from);
+               /*
+                * reservedtop=size reserves a hole at the top of the kernel
+                * address space which a hypervisor can load into later.
+                * Needed for dynamically loaded hypervisors, so relocating
+                * the fixmap can be done before paging initialization.
+                * This hole must be a multiple of 4M.
+                */
+               else if (!memcmp(from, "reservedtop=", 12)) {
+                       unsigned long reserved = memparse(from+12, &from);
+                       reserved &= ~0x3fffff;
+                       set_fixaddr_top(-reserved);
+               }
                c = *(from++);
                if (!c)

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