[RFC 02/15] x86_64: Fold pda into per cpu area

From: Mike Travis
Date: Wed Jul 09 2008 - 12:52:19 EST

WARNING: there is still a FIXME in this patch (see arch/x86/kernel/acpi/sleep.c)

* Declare the pda as a per cpu variable.

* Make the x86_64 per cpu area start at zero.

* Relocate the initial pda and per_cpu(gdt_page) in head_64.S for the
boot cpu (0). For secondary cpus, do_boot_cpu() sets up the correct
initial pda and gdt_page pointer.

* Initialize per_cpu_offset to point to static pda in the per_cpu area
(@ __per_cpu_load).

* After allocation of the per cpu area for the boot cpu (0), reload the
gdt page pointer.

Based on linux-2.6.tip/master

Signed-off-by: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Mike Travis <travis@xxxxxxx>
---
arch/x86/Kconfig | 3 +
arch/x86/kernel/acpi/sleep.c | 9 +++
arch/x86/kernel/cpu/common_64.c | 4 -
arch/x86/kernel/head64.c | 24 +--------
arch/x86/kernel/head_64.S | 45 ++++++++++++++++--
arch/x86/kernel/setup_percpu.c | 94 +++++++++++++++++----------------------
arch/x86/kernel/smpboot.c | 52 ---------------------
arch/x86/kernel/vmlinux_64.lds.S | 1
include/asm-x86/desc.h | 5 ++
include/asm-x86/pda.h | 3 -
include/asm-x86/percpu.h | 13 -----
include/asm-x86/trampoline.h | 1
12 files changed, 112 insertions(+), 142 deletions(-)

--- linux-2.6.tip.orig/arch/x86/Kconfig
+++ linux-2.6.tip/arch/x86/Kconfig
@@ -129,6 +129,9 @@ config HAVE_SETUP_PER_CPU_AREA
config HAVE_CPUMASK_OF_CPU_MAP
def_bool X86_64_SMP

+config HAVE_ZERO_BASED_PER_CPU
+ def_bool X86_64_SMP
+
config ARCH_HIBERNATION_POSSIBLE
def_bool y
depends on !SMP || !X86_VOYAGER
--- linux-2.6.tip.orig/arch/x86/kernel/acpi/sleep.c
+++ linux-2.6.tip/arch/x86/kernel/acpi/sleep.c
@@ -89,6 +89,15 @@ int acpi_save_state_mem(void)
#ifdef CONFIG_SMP
stack_start.sp = temp_stack + 4096;
#endif
+ /*
+ * FIXME: with zero-based percpu variables, the pda and gdt_page
+ * addresses must be offset by the base of this cpu's percpu area.
+ * Where/how should we do this?
+ *
+ * for secondary cpu startup in smpboot.c:do_boot_cpu() this is done:
+ * early_gdt_descr.address = (unsigned long)get_cpu_gdt_table(cpu);
+ * initial_pda = (unsigned long)get_cpu_pda(cpu);
+ */
initial_code = (unsigned long)wakeup_long64;
saved_magic = 0x123456789abcdef0;
#endif /* CONFIG_64BIT */
--- linux-2.6.tip.orig/arch/x86/kernel/cpu/common_64.c
+++ linux-2.6.tip/arch/x86/kernel/cpu/common_64.c
@@ -423,8 +423,8 @@ __setup("clearcpuid=", setup_disablecpui

cpumask_t cpu_initialized __cpuinitdata = CPU_MASK_NONE;

-struct x8664_pda **_cpu_pda __read_mostly;
-EXPORT_SYMBOL(_cpu_pda);
+DEFINE_PER_CPU_FIRST(struct x8664_pda, pda);
+EXPORT_PER_CPU_SYMBOL(pda);

struct desc_ptr idt_descr = { 256 * 16 - 1, (unsigned long) idt_table };

--- linux-2.6.tip.orig/arch/x86/kernel/head64.c
+++ linux-2.6.tip/arch/x86/kernel/head64.c
@@ -25,20 +25,6 @@
#include <asm/e820.h>
#include <asm/bios_ebda.h>

-/* boot cpu pda */
-static struct x8664_pda _boot_cpu_pda __read_mostly;
-
-#ifdef CONFIG_SMP
-/*
- * We install an empty cpu_pda pointer table to indicate to early users
- * (numa_set_node) that the cpu_pda pointer table for cpus other than
- * the boot cpu is not yet setup.
- */
-static struct x8664_pda *__cpu_pda[NR_CPUS] __initdata;
-#else
-static struct x8664_pda *__cpu_pda[NR_CPUS] __read_mostly;
-#endif
-
static void __init zap_identity_mappings(void)
{
pgd_t *pgd = pgd_offset_k(0UL);
@@ -91,6 +77,10 @@ void __init x86_64_start_kernel(char * r
/* Cleanup the over mapped high alias */
cleanup_highmap();

+ /* Initialize boot cpu_pda data */
+ /* (See head_64.S for earlier pda/gdt initialization) */
+ pda_init(0);
+
for (i = 0; i < NUM_EXCEPTION_VECTORS; i++) {
#ifdef CONFIG_EARLY_PRINTK
set_intr_gate(i, &early_idt_handlers[i]);
@@ -102,12 +92,6 @@ void __init x86_64_start_kernel(char * r

early_printk("Kernel alive\n");

- _cpu_pda = __cpu_pda;
- cpu_pda(0) = &_boot_cpu_pda;
- pda_init(0);
-
- early_printk("Kernel really alive\n");
-
copy_bootdata(__va(real_mode_data));

reserve_early(__pa_symbol(&_text), __pa_symbol(&_end), "TEXT DATA BSS");
--- linux-2.6.tip.orig/arch/x86/kernel/head_64.S
+++ linux-2.6.tip/arch/x86/kernel/head_64.S
@@ -12,6 +12,7 @@
#include <linux/linkage.h>
#include <linux/threads.h>
#include <linux/init.h>
+#include <asm/asm-offsets.h>
#include <asm/desc.h>
#include <asm/segment.h>
#include <asm/pgtable.h>
@@ -203,7 +204,27 @@ ENTRY(secondary_startup_64)
* addresses where we're currently running on. We have to do that here
* because in 32bit we couldn't load a 64bit linear address.
*/
- lgdt early_gdt_descr(%rip)
+
+#ifdef CONFIG_SMP
+ /*
+ * For zero-based percpu variables, the base (__per_cpu_load) must
+ * be added to the offset of per_cpu__gdt_page. This is only needed
+ * for the boot cpu but we can't do this prior to secondary_startup_64.
+ * So we use a NULL gdt adrs to indicate that we are starting up the
+ * boot cpu and not the secondary cpus. do_boot_cpu() will fixup
+ * the gdt adrs for those cpus.
+ */
+#define PER_CPU_GDT_PAGE 0
+ 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)
+#else
+#define PER_CPU_GDT_PAGE per_cpu__gdt_page
+#endif
+1: lgdt early_gdt_descr(%rip)

/* set up data segments. actually 0 would do too */
movl $__KERNEL_DS,%eax
@@ -220,14 +241,21 @@ ENTRY(secondary_startup_64)
movl %eax,%gs

/*
- * Setup up a dummy PDA. this is just for some early bootup code
- * that does in_interrupt()
+ * Setup up the real PDA.
+ *
+ * For SMP, the boot cpu (0) uses the static pda which is the first
+ * element in the percpu area (@__per_cpu_load). This pda is moved
+ * to the real percpu area once that is allocated. Secondary cpus
+ * will use the initial_pda value setup in do_boot_cpu().
*/
movl $MSR_GS_BASE,%ecx
- movq $empty_zero_page,%rax
+ movq initial_pda(%rip), %rax
movq %rax,%rdx
shrq $32,%rdx
wrmsr
+#ifdef CONFIG_SMP
+ movq %rax, %gs:pda_data_offset
+#endif

/* esi is pointer to real mode structure with interesting info.
pass it to C */
@@ -250,6 +278,12 @@ ENTRY(secondary_startup_64)
.align 8
ENTRY(initial_code)
.quad x86_64_start_kernel
+ ENTRY(initial_pda)
+#ifdef CONFIG_SMP
+ .quad __per_cpu_load # Overwritten for secondary CPUs
+#else
+ .quad per_cpu__pda
+#endif
__FINITDATA

ENTRY(stack_start)
@@ -394,7 +428,8 @@ NEXT_PAGE(level2_spare_pgt)
.globl early_gdt_descr
early_gdt_descr:
.word GDT_ENTRIES*8-1
- .quad per_cpu__gdt_page
+early_gdt_descr_base:
+ .quad PER_CPU_GDT_PAGE # Overwritten for secondary CPUs

ENTRY(phys_base)
/* This must match the first entry in level2_kernel_pgt */
--- linux-2.6.tip.orig/arch/x86/kernel/setup_percpu.c
+++ linux-2.6.tip/arch/x86/kernel/setup_percpu.c
@@ -14,6 +14,7 @@
#include <asm/mpspec.h>
#include <asm/apicdef.h>
#include <asm/highmem.h>
+#include <asm/desc.h>

#ifdef CONFIG_DEBUG_PER_CPU_MAPS
# define DBG(x...) printk(KERN_DEBUG x)
@@ -119,63 +120,26 @@ static void __init setup_cpumask_of_cpu(
static inline void setup_cpumask_of_cpu(void) { }
#endif

-#ifdef CONFIG_X86_32
/*
- * Great future not-so-futuristic plan: make i386 and x86_64 do it
- * the same way
+ * Pointers to per cpu areas for each cpu
*/
+#ifndef CONFIG_HAVE_ZERO_BASED_PER_CPU
unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
EXPORT_SYMBOL(__per_cpu_offset);
-static inline void setup_cpu_pda_map(void) { }
-
-#elif !defined(CONFIG_SMP)
-static inline void setup_cpu_pda_map(void) { }
-
-#else /* CONFIG_SMP && CONFIG_X86_64 */
+#else

/*
- * Allocate cpu_pda pointer table and array via alloc_bootmem.
+ * Initialize percpu offset for boot cpu (0) to static percpu area
+ * for referencing very early in kernel startup.
*/
-static void __init setup_cpu_pda_map(void)
-{
- char *pda;
- struct x8664_pda **new_cpu_pda;
- unsigned long size;
- int cpu;
-
- size = roundup(sizeof(struct x8664_pda), cache_line_size());
-
- /* allocate cpu_pda array and pointer table */
- {
- unsigned long tsize = nr_cpu_ids * sizeof(void *);
- unsigned long asize = size * (nr_cpu_ids - 1);
-
- tsize = roundup(tsize, cache_line_size());
- new_cpu_pda = alloc_bootmem(tsize + asize);
- pda = (char *)new_cpu_pda + tsize;
- }
-
- /* initialize pointer table to static pda's */
- for_each_possible_cpu(cpu) {
- if (cpu == 0) {
- /* leave boot cpu pda in place */
- new_cpu_pda[0] = cpu_pda(0);
- continue;
- }
- new_cpu_pda[cpu] = (struct x8664_pda *)pda;
- new_cpu_pda[cpu]->in_bootmem = 1;
- pda += size;
- }
-
- /* point to new pointer table */
- _cpu_pda = new_cpu_pda;
-}
+unsigned long __per_cpu_offset[NR_CPUS] __read_mostly = {
+ [0] = (unsigned long)__per_cpu_load
+};
+EXPORT_SYMBOL(__per_cpu_offset);
#endif

/*
- * Great future plan:
- * Declare PDA itself and support (irqstack,tss,pgd) as per cpu data.
- * Always point %gs to its beginning
+ * Allocate and initialize the per cpu areas which include the PDAs.
*/
void __init setup_per_cpu_areas(void)
{
@@ -193,9 +157,6 @@ void __init setup_per_cpu_areas(void)
nr_cpu_ids = num_processors;
#endif

- /* Setup cpu_pda map */
- setup_cpu_pda_map();
-
/* Copy section for each CPU (we discard the original) */
size = PERCPU_ENOUGH_ROOM;
printk(KERN_INFO "PERCPU: Allocating %zd bytes of per cpu data\n",
@@ -215,10 +176,41 @@ void __init setup_per_cpu_areas(void)
else
ptr = alloc_bootmem_pages_node(NODE_DATA(node), size);
#endif
+ /* Initialize each cpu's per_cpu area and save pointer */
+ memcpy(ptr, __per_cpu_load, __per_cpu_size);
per_cpu_offset(cpu) = ptr - __per_cpu_start;
- memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start);

DBG("PERCPU: cpu %4d %p\n", cpu, ptr);
+
+#ifdef CONFIG_X86_64
+ /*
+ * Note the boot cpu (0) has been using the static per_cpu load
+ * area for it's pda. We need to zero out the pdas for the
+ * other cpus that are coming online.
+ *
+ * Additionally, for the boot cpu the gdt page must be reloaded
+ * as we moved it from the static per cpu area to the newly
+ * allocated area.
+ */
+ {
+ /* We rely on the fact that pda is the first element */
+ struct x8664_pda *pda = (struct x8664_pda *)ptr;
+
+ if (cpu) {
+ memset(pda, 0, sizeof(*pda));
+ pda->data_offset = (unsigned long)ptr;
+ } else {
+ struct desc_ptr gdt_descr = early_gdt_descr;
+
+ pda->data_offset = (unsigned long)ptr;
+ gdt_descr.address =
+ (unsigned long)get_cpu_gdt_table(0);
+ native_load_gdt(&gdt_descr);
+ pda_init(0);
+ }
+
+ }
+#endif
}

printk(KERN_INFO "NR_CPUS: %d, nr_cpu_ids: %d, nr_node_ids %d\n",
--- linux-2.6.tip.orig/arch/x86/kernel/smpboot.c
+++ linux-2.6.tip/arch/x86/kernel/smpboot.c
@@ -762,45 +762,6 @@ static void __cpuinit do_fork_idle(struc
complete(&c_idle->done);
}

-#ifdef CONFIG_X86_64
-/*
- * Allocate node local memory for the AP pda.
- *
- * Must be called after the _cpu_pda pointer table is initialized.
- */
-static int __cpuinit get_local_pda(int cpu)
-{
- struct x8664_pda *oldpda, *newpda;
- unsigned long size = sizeof(struct x8664_pda);
- int node = cpu_to_node(cpu);
-
- if (cpu_pda(cpu) && !cpu_pda(cpu)->in_bootmem)
- return 0;
-
- oldpda = cpu_pda(cpu);
- newpda = kmalloc_node(size, GFP_ATOMIC, node);
- if (!newpda) {
- printk(KERN_ERR "Could not allocate node local PDA "
- "for CPU %d on node %d\n", cpu, node);
-
- if (oldpda)
- return 0; /* have a usable pda */
- else
- return -1;
- }
-
- if (oldpda) {
- memcpy(newpda, oldpda, size);
- if (!after_bootmem)
- free_bootmem((unsigned long)oldpda, size);
- }
-
- newpda->in_bootmem = 0;
- cpu_pda(cpu) = newpda;
- return 0;
-}
-#endif /* CONFIG_X86_64 */
-
static int __cpuinit do_boot_cpu(int apicid, int cpu)
/*
* NOTE - on most systems this is a PHYSICAL apic ID, but on multiquad
@@ -818,16 +779,6 @@ static int __cpuinit do_boot_cpu(int api
};
INIT_WORK(&c_idle.work, do_fork_idle);

-#ifdef CONFIG_X86_64
- /* Allocate node local memory for AP pdas */
- if (cpu > 0) {
- boot_error = get_local_pda(cpu);
- if (boot_error)
- goto restore_state;
- /* if can't get pda memory, can't start cpu */
- }
-#endif
-
alternatives_smp_switch(1);

c_idle.idle = get_idle_for_cpu(cpu);
@@ -865,6 +816,7 @@ do_rest:
#else
cpu_pda(cpu)->pcurrent = c_idle.idle;
clear_tsk_thread_flag(c_idle.idle, TIF_FORK);
+ initial_pda = (unsigned long)get_cpu_pda(cpu);
#endif
early_gdt_descr.address = (unsigned long)get_cpu_gdt_table(cpu);
initial_code = (unsigned long)start_secondary;
@@ -940,8 +892,6 @@ do_rest:
}
}

-restore_state:
-
if (boot_error) {
/* Try to put things back the way they were before ... */
numa_remove_cpu(cpu); /* was set by numa_add_cpu */
--- linux-2.6.tip.orig/arch/x86/kernel/vmlinux_64.lds.S
+++ linux-2.6.tip/arch/x86/kernel/vmlinux_64.lds.S
@@ -16,6 +16,7 @@ jiffies_64 = jiffies;
_proxy_pda = 1;
PHDRS {
text PT_LOAD FLAGS(5); /* R_E */
+ percpu PT_LOAD FLAGS(7); /* RWE */
data PT_LOAD FLAGS(7); /* RWE */
user PT_LOAD FLAGS(7); /* RWE */
data.init PT_LOAD FLAGS(7); /* RWE */
--- linux-2.6.tip.orig/include/asm-x86/desc.h
+++ linux-2.6.tip/include/asm-x86/desc.h
@@ -41,6 +41,11 @@ static inline struct desc_struct *get_cp

#ifdef CONFIG_X86_64

+static inline struct x8664_pda *get_cpu_pda(unsigned int cpu)
+{
+ return &per_cpu(pda, cpu);
+}
+
static inline void pack_gate(gate_desc *gate, unsigned type, unsigned long func,
unsigned dpl, unsigned ist, unsigned seg)
{
--- linux-2.6.tip.orig/include/asm-x86/pda.h
+++ linux-2.6.tip/include/asm-x86/pda.h
@@ -37,10 +37,9 @@ struct x8664_pda {
unsigned irq_spurious_count;
} ____cacheline_aligned_in_smp;

-extern struct x8664_pda **_cpu_pda;
extern void pda_init(int);

-#define cpu_pda(i) (_cpu_pda[i])
+#define cpu_pda(cpu) (&per_cpu(pda, cpu))

/*
* There is no fast way to get the base address of the PDA, all the accesses
--- linux-2.6.tip.orig/include/asm-x86/percpu.h
+++ linux-2.6.tip/include/asm-x86/percpu.h
@@ -3,20 +3,11 @@

#ifdef CONFIG_X86_64
#include <linux/compiler.h>
-
-/* Same as asm-generic/percpu.h, except that we store the per cpu offset
- in the PDA. Longer term the PDA and every per cpu variable
- should be just put into a single section and referenced directly
- from %gs */
-
-#ifdef CONFIG_SMP
#include <asm/pda.h>

-#define __per_cpu_offset(cpu) (cpu_pda(cpu)->data_offset)
+/* Same as asm-generic/percpu.h */
+#ifdef CONFIG_SMP
#define __my_cpu_offset read_pda(data_offset)
-
-#define per_cpu_offset(x) (__per_cpu_offset(x))
-
#endif
#include <asm-generic/percpu.h>

--- linux-2.6.tip.orig/include/asm-x86/trampoline.h
+++ linux-2.6.tip/include/asm-x86/trampoline.h
@@ -12,6 +12,7 @@ extern unsigned char *trampoline_base;

extern unsigned long init_rsp;
extern unsigned long initial_code;
+extern unsigned long initial_pda;

#define TRAMPOLINE_BASE 0x6000
extern unsigned long setup_trampoline(void);

--
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