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Date: Tue, 13 Jan 2009 19:38:09 +0900
From: Tejun Heo <tj@...nel.org>
To: ebiederm@...ssion.com, cl@...ux-foundation.org,
rusty@...tcorp.com.au, mingo@...e.hu, travis@....com,
linux-kernel@...r.kernel.org, hpa@...or.com,
akpm@...ux-foundation.org, steiner@....com, hugh@...itas.com
Cc: Tejun Heo <tj@...nel.org>
Subject: [PATCH 05/13] x86_64: make percpu symbols zerobased on SMP
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@...nel.org>
Cc: Mike Travis <travis@....com>
---
arch/x86/kernel/head64.c | 2 +
arch/x86/kernel/head_64.S | 24 ++++++++++++++++-
arch/x86/kernel/setup_percpu.c | 2 +-
arch/x86/kernel/vmlinux_64.lds.S | 17 +++++++++++-
include/asm-generic/sections.h | 2 +-
include/asm-generic/vmlinux.lds.h | 51 ++++++++++++++++++++++++++++++++----
6 files changed, 88 insertions(+), 10 deletions(-)
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 388e05a..a63261b 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -44,6 +44,8 @@ void __init x86_64_init_pda(void)
{
_cpu_pda = __cpu_pda;
cpu_pda(0) = &_boot_cpu_pda;
+ cpu_pda(0)->data_offset =
+ (unsigned long)(__per_cpu_load - __per_cpu_start);
pda_init(0);
}
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 26cfdc1..5ab77b3 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -204,6 +204,23 @@ ENTRY(secondary_startup_64)
pushq $0
popfq
+#ifdef CONFIG_SMP
+ /*
+ * early_gdt_base should point to the gdt_page in static percpu init
+ * data area. Computing this requires two symbols - __per_cpu_load
+ * and per_cpu__gdt_page. As linker can't do no such relocation, do
+ * it by hand. As early_gdt_descr is manipulated by C code for
+ * secondary CPUs, this should be done only once for the boot CPU
+ * when early_gdt_descr_base contains zero.
+ */
+ movq early_gdt_descr_base(%rip), %rax
+ testq %rax, %rax
+ jnz 1f
+ movq $__per_cpu_load, %rax
+ addq $per_cpu__gdt_page, %rax
+ movq %rax, early_gdt_descr_base(%rip)
+1:
+#endif
/*
* We must switch to a new descriptor in kernel space for the GDT
* because soon the kernel won't have access anymore to the userspace
@@ -401,7 +418,12 @@ NEXT_PAGE(level2_spare_pgt)
.globl early_gdt_descr
early_gdt_descr:
.word GDT_ENTRIES*8-1
- .quad per_cpu__gdt_page
+#ifdef CONFIG_SMP
+early_gdt_descr_base:
+ .quad 0x0000000000000000
+#else
+ .quad per_cpu__gdt_page
+#endif
ENTRY(phys_base)
/* This must match the first entry in level2_kernel_pgt */
diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
index ee55e3b..8a22c94 100644
--- a/arch/x86/kernel/setup_percpu.c
+++ b/arch/x86/kernel/setup_percpu.c
@@ -194,7 +194,7 @@ void __init setup_per_cpu_areas(void)
}
#endif
per_cpu_offset(cpu) = ptr - __per_cpu_start;
- memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start);
+ memcpy(ptr, __per_cpu_load, __per_cpu_end - __per_cpu_start);
DBG("PERCPU: cpu %4d %p\n", cpu, ptr);
}
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 @@ PHDRS {
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 @@ SECTIONS
__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 = .;
diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
index 79a7ff9..4ce48e8 100644
--- a/include/asm-generic/sections.h
+++ b/include/asm-generic/sections.h
@@ -9,7 +9,7 @@ extern char __bss_start[], __bss_stop[];
extern char __init_begin[], __init_end[];
extern char _sinittext[], _einittext[];
extern char _end[];
-extern char __per_cpu_start[], __per_cpu_end[];
+extern char __per_cpu_load[], __per_cpu_start[], __per_cpu_end[];
extern char __kprobes_text_start[], __kprobes_text_end[];
extern char __initdata_begin[], __initdata_end[];
extern char __start_rodata[], __end_rodata[];
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index c61fab1..fc2f55f 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -430,12 +430,51 @@
*(.initcall7.init) \
*(.initcall7s.init)
-#define PERCPU(align) \
- . = ALIGN(align); \
- VMLINUX_SYMBOL(__per_cpu_start) = .; \
- .data.percpu : AT(ADDR(.data.percpu) - LOAD_OFFSET) { \
+#define PERCPU_PROLOG(vaddr) \
+ VMLINUX_SYMBOL(__per_cpu_load) = .; \
+ .data.percpu vaddr : AT(__per_cpu_load - LOAD_OFFSET) { \
+ VMLINUX_SYMBOL(__per_cpu_start) = .;
+
+#define PERCPU_EPILOG(phdr) \
+ VMLINUX_SYMBOL(__per_cpu_end) = .; \
+ } phdr \
+ . = __per_cpu_load + SIZEOF(.data.percpu);
+
+/**
+ * PERCPU_VADDR - define output section for percpu area
+ * @vaddr: explicit base address (optional)
+ * @phdr: destination PHDR (optional)
+ *
+ * Macro which expands to output section for percpu area. If @vaddr
+ * is not blank, it specifies explicit base address and all percpu
+ * symbols will be offset from the given address. If blank, @vaddr
+ * always equals @laddr + LOAD_OFFSET.
+ *
+ * @phdr defines the output PHDR to use if not blank. Be warned that
+ * output PHDR is sticky. If @phdr is specified, the next output
+ * section in the linker script will go there too. @phdr should have
+ * a leading colon.
+ *
+ * This macro defines three symbols, __per_cpu_load, __per_cpu_start
+ * and __per_cpu_end. The first one is the vaddr of loaded percpu
+ * init data. __per_cpu_start equals @vaddr and __per_cpu_end is the
+ * end offset.
+ */
+#define PERCPU_VADDR(vaddr, phdr) \
+ PERCPU_PROLOG(vaddr) \
*(.data.percpu.page_aligned) \
*(.data.percpu) \
*(.data.percpu.shared_aligned) \
- } \
- VMLINUX_SYMBOL(__per_cpu_end) = .;
+ PERCPU_EPILOG(phdr)
+
+/**
+ * PERCPU - define output section for percpu area, simple version
+ * @align: required alignment
+ *
+ * Align to @align and outputs output section for percpu area. This
+ * macro doesn't maniuplate @vaddr or @phdr and __per_cpu_load and
+ * __per_cpu_start will be identical.
+ */
+#define PERCPU(align) \
+ . = ALIGN(align); \
+ PERCPU_VADDR( , )
--
1.5.6
--
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