[PATCH] x86: GDT alignment fix

Make GDT page aligned and page padded to support running inside of a
hypervisor.  This prevents false sharing of the GDT page with other hot
data, which is not allowed in Xen, and causes performance problems in
VMware.

Rather than go back to the old method of statically allocating the GDT
(which wastes unneded space for non-present CPUs), the GDT for APs is
allocated dynamically.

Signed-off-by: Zachary Amsden <zach@vmware.com>
Cc: "Seth, Rohit" <rohit.seth@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/i386/kernel/apm.c b/arch/i386/kernel/apm.c
index 1e60acbed3c1..6c8e483ce9e4 100644
--- a/arch/i386/kernel/apm.c
+++ b/arch/i386/kernel/apm.c
@@ -2317,6 +2317,8 @@ static int __init apm_init(void)
 
         for (i = 0; i < NR_CPUS; i++) {
                 struct desc_struct *gdt = get_cpu_gdt_table(i);
+                if (!gdt)
+                        continue;
                 set_base(gdt[APM_CS >> 3],
                          __va((unsigned long)apm_info.bios.cseg << 4));
                 set_base(gdt[APM_CS_16 >> 3],