Re: [patch 7/8] Add a bootparameter to reserve high linear address space.

Zachary Amsden
2006-08-03T08:58:34Z

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Andrew Morton wrote:
> The comment says "must". If that's true then printing a what-you-did-wrong
> message and halting is appropriate.
>
> But whatever. The issue is flagged and I'm happy to leave it in Jeremy's
> lap.

Considering I wrote that patch, I think I should fix it -- here you go

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Subject: Add a bootparameter to reserve high linear address space.

Add a bootparameter to reserve high linear address space for hypervisors.
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
space.

Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>

---
Documentation/kernel-parameters.txt | 5 +++++
arch/i386/kernel/setup.c | 19 +++++++++++++++++++
2 files changed, 24 insertions(+)

diff -r 5bb2fc59943d Documentation/kernel-parameters.txt
--- a/Documentation/kernel-parameters.txt Thu Aug 03 01:36:13 2006 -0700
+++ b/Documentation/kernel-parameters.txt Thu Aug 03 01:36:13 2006 -0700
@@ -1357,6 +1357,11 @@ running once the system is up.

reserve= [KNL,BUGS] Force the kernel to ignore some iomem area

+ reservetop= [IA-32]
+ Format: nn[KMG]
+ Reserves a hole at the top of the kernel virtual
+ address space.
+
resume= [SWSUSP]
Specify the partition device for software suspend

diff -r 5bb2fc59943d arch/i386/kernel/setup.c
--- a/arch/i386/kernel/setup.c Thu Aug 03 01:36:13 2006 -0700
+++ b/arch/i386/kernel/setup.c Thu Aug 03 01:36:52 2006 -0700
@@ -160,6 +160,12 @@ static char command_line[COMMAND_LINE_SI
static char command_line[COMMAND_LINE_SIZE];

unsigned char __initdata boot_params[PARAM_SIZE];
+
+static int __init setup_reservetop(char *s)
+{
+ return 1;
+}
+__setup("reservetop", setup_reservetop);

static struct resource data_resource = {
.name = "Kernel data",
@@ -917,6 +923,17 @@ static void __init parse_cmdline_early (
else if (!memcmp(from, "vmalloc=", 8))
__VMALLOC_RESERVE = memparse(from+8, &from);

+ /*
+ * reservetop=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.
+ */
+ else if (!memcmp(from, "reservetop=", 11)) {
+ unsigned long reserve = memparse(from+11, &from);
+ reserve_top_address(reserve);
+ }
+
next_char:
c = *(from++);
if (!c)