x86: make percpu symbols zerobased on SMP
[ Based on original patch from Christoph Lameter and Mike Travis. ]
This patch makes percpu symbols zerobased on x86_64 SMP by adding
PERCPU_VADDR() to vmlinux.lds.h which helps setting explicit vaddr on
the percpu output section and using it in vmlinux_64.lds.S. A new
PHDR is added as existing ones cannot contain sections near address
zero. PERCPU_VADDR() also adds a new symbol __per_cpu_load which
always points to the vaddr of the loaded percpu data.init region.
The following adjustments have been made to accomodate the address
change.
* code to locate percpu gdt_page in head_64.S is updated to add the
load address to the gdt_page offset.
* __per_cpu_load is used in places where access to the init data area
is necessary.
* pda->data_offset is initialized soon after C code is entered as zero
value doesn't work anymore.
This patch is mostly taken from Mike Travis' "x86_64: Base percpu
variables at zero" patch.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/vmlinux_64.lds.S b/arch/x86/kernel/vmlinux_64.lds.S
index 1a614c0..f50280d 100644
--- a/arch/x86/kernel/vmlinux_64.lds.S
+++ b/arch/x86/kernel/vmlinux_64.lds.S
@@ -19,6 +19,9 @@
data PT_LOAD FLAGS(7); /* RWE */
user PT_LOAD FLAGS(7); /* RWE */
data.init PT_LOAD FLAGS(7); /* RWE */
+#ifdef CONFIG_SMP
+ percpu PT_LOAD FLAGS(7); /* RWE */
+#endif
note PT_NOTE FLAGS(0); /* ___ */
}
SECTIONS
@@ -208,14 +211,26 @@
__initramfs_end = .;
#endif
+#ifdef CONFIG_SMP
+ /*
+ * percpu offsets are zero-based on SMP. PERCPU_VADDR() changes the
+ * output PHDR, so the next output section - __data_nosave - should
+ * switch it back to data.init.
+ */
+ . = ALIGN(PAGE_SIZE);
+ PERCPU_VADDR(0, :percpu)
+#else
PERCPU(PAGE_SIZE)
+#endif
. = ALIGN(PAGE_SIZE);
__init_end = .;
. = ALIGN(PAGE_SIZE);
__nosave_begin = .;
- .data_nosave : AT(ADDR(.data_nosave) - LOAD_OFFSET) { *(.data.nosave) }
+ .data_nosave : AT(ADDR(.data_nosave) - LOAD_OFFSET) {
+ *(.data.nosave)
+ } :data.init /* switch back to data.init, see PERCPU_VADDR() above */
. = ALIGN(PAGE_SIZE);
__nosave_end = .;