x86, trampoline: Common infrastructure for low memory trampolines

Common infrastructure for low memory trampolines.  This code installs
the trampolines permanently in low memory very early.  It also permits
multiple pieces of code to be used for this purpose.

This code also introduces a standard infrastructure for computing
symbol addresses in the trampoline code.

The only change to the actual SMP trampolines themselves is that the
64-bit trampoline has been made reusable -- the previous version would
overwrite the code with a status variable; this moves the status
variable to a separate location.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
LKML-Reference: <4D5DFBE4.7090104@intel.com>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Matthieu Castet <castet.matthieu@free.fr>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>

1 files changed, 11 insertions, 4 deletions

diff --git a/arch/x86/kernel/trampoline_32.S b/arch/x86/kernel/trampoline_32.S
index 8508237e8e43..451c0a7ef7fd 100644
--- a/arch/x86/kernel/trampoline_32.S
+++ b/arch/x86/kernel/trampoline_32.S
@@ -32,9 +32,11 @@
 #include <asm/segment.h>
 #include <asm/page_types.h>
 
-/* We can free up trampoline after bootup if cpu hotplug is not supported. */
-__CPUINITRODATA
-.code16
+#ifdef CONFIG_SMP
+
+        .section ".x86_trampoline","a"
+        .balign PAGE_SIZE
+        .code16
 
 ENTRY(trampoline_data)
 r_base = .
@@ -44,7 +46,7 @@ r_base = .
 
         cli                     # We should be safe anyway
 
-        movl    $0xA5A5A5A5, trampoline_data - r_base
+        movl    $0xA5A5A5A5, trampoline_status - r_base
                                 # write marker for master knows we're running
 
         /* GDT tables in non default location kernel can be beyond 16MB and
@@ -72,5 +74,10 @@ boot_idt_descr:
         .word   0                               # idt limit = 0
         .long   0                               # idt base = 0L
 
+ENTRY(trampoline_status)
+        .long   0
+
 .globl trampoline_end
 trampoline_end:
+
+#endif /* CONFIG_SMP */