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 <[email protected]>
Signed-off-by: Chris Wright <[email protected]>
---
Documentation/kernel-parameters.txt | 5 +++++
arch/i386/kernel/setup.c | 19 +++++++++++++++++++
2 files changed, 24 insertions(+)
===================================================================
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -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
===================================================================
--- a/arch/i386/kernel/setup.c
+++ b/arch/i386/kernel/setup.c
@@ -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 +923,19 @@ 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.
+ * This hole must be a multiple of 4M.
+ */
+ else if (!memcmp(from, "reservetop=", 11)) {
+ unsigned long reserve = memparse(from+11, &from);
+ reserve &= ~0x3fffff;
+ reserve_top_address(reserve);
+ }
+
next_char:
c = *(from++);
if (!c)
--
-
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