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Subject[PATCH] [31/48] i386: Use per-cpu GDT immediately upon boot
Date

From: Rusty Russell <rusty@rustcorp.com.au>

Now we are no longer dynamically allocating the GDT, we don't need the
"cpu_gdt_table" at all: we can switch straight from "boot_gdt_table" to the
per-cpu GDT. This means initializing the cpu_gdt array in C.

The boot CPU uses the per-cpu var directly, then in smp_prepare_cpus() it
switches to the per-cpu copy just allocated. For secondary CPUs, the
early_gdt_descr is set to point directly to their per-cpu copy.

For UP the code is very simple: it keeps using the "per-cpu" GDT as per SMP,
but we never have to move.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
arch/i386/kernel/cpu/common.c | 72 +++++++++++++----------------------
arch/i386/kernel/head.S | 55 --------------------------
arch/i386/kernel/smpboot.c | 59 ++++++++++++++++++++++------
arch/i386/mach-voyager/voyager_smp.c | 6 --
include/asm-i386/desc.h | 2
include/asm-i386/processor.h | 1
6 files changed, 75 insertions(+), 120 deletions(-)
Index: linux/arch/i386/kernel/cpu/common.c
===================================================================
--- linux.orig/arch/i386/kernel/cpu/common.c
+++ linux/arch/i386/kernel/cpu/common.c
@@ -25,7 +25,33 @@
DEFINE_PER_CPU(struct Xgt_desc_struct, cpu_gdt_descr);
EXPORT_PER_CPU_SYMBOL(cpu_gdt_descr);

-DEFINE_PER_CPU(struct desc_struct, cpu_gdt[GDT_ENTRIES]);
+DEFINE_PER_CPU(struct desc_struct, cpu_gdt[GDT_ENTRIES]) = {
+ [GDT_ENTRY_KERNEL_CS] = { 0x0000ffff, 0x00cf9a00 },
+ [GDT_ENTRY_KERNEL_DS] = { 0x0000ffff, 0x00cf9200 },
+ [GDT_ENTRY_DEFAULT_USER_CS] = { 0x0000ffff, 0x00cffa00 },
+ [GDT_ENTRY_DEFAULT_USER_DS] = { 0x0000ffff, 0x00cff200 },
+ /*
+ * Segments used for calling PnP BIOS have byte granularity.
+ * They code segments and data segments have fixed 64k limits,
+ * the transfer segment sizes are set at run time.
+ */
+ [GDT_ENTRY_PNPBIOS_CS32] = { 0x0000ffff, 0x00409a00 },/* 32-bit code */
+ [GDT_ENTRY_PNPBIOS_CS16] = { 0x0000ffff, 0x00009a00 },/* 16-bit code */
+ [GDT_ENTRY_PNPBIOS_DS] = { 0x0000ffff, 0x00009200 }, /* 16-bit data */
+ [GDT_ENTRY_PNPBIOS_TS1] = { 0x00000000, 0x00009200 },/* 16-bit data */
+ [GDT_ENTRY_PNPBIOS_TS2] = { 0x00000000, 0x00009200 },/* 16-bit data */
+ /*
+ * The APM segments have byte granularity and their bases
+ * are set at run time. All have 64k limits.
+ */
+ [GDT_ENTRY_APMBIOS_BASE] = { 0x0000ffff, 0x00409a00 },/* 32-bit code */
+ /* 16-bit code */
+ [GDT_ENTRY_APMBIOS_BASE+1] = { 0x0000ffff, 0x00009a00 },
+ [GDT_ENTRY_APMBIOS_BASE+2] = { 0x0000ffff, 0x00409200 }, /* data */
+
+ [GDT_ENTRY_ESPFIX_SS] = { 0x00000000, 0x00c09200 },
+ [GDT_ENTRY_PDA] = { 0x00000000, 0x00c09200 }, /* set in setup_pda */
+};

DEFINE_PER_CPU(struct i386_pda, _cpu_pda);
EXPORT_PER_CPU_SYMBOL(_cpu_pda);
@@ -618,46 +644,6 @@ struct i386_pda boot_pda = {
.pcurrent = &init_task,
};

-static inline void set_kernel_fs(void)
-{
- /* Set %fs for this CPU's PDA. Memory clobber is to create a
- barrier with respect to any PDA operations, so the compiler
- doesn't move any before here. */
- asm volatile ("mov %0, %%fs" : : "r" (__KERNEL_PDA) : "memory");
-}
-
-/* Initialize the CPU's GDT and PDA. This is either the boot CPU doing itself
- (still using cpu_gdt_table), or a CPU doing it for a secondary which
- will soon come up. */
-__cpuinit void init_gdt(int cpu, struct task_struct *idle)
-{
- struct Xgt_desc_struct *cpu_gdt_descr = &per_cpu(cpu_gdt_descr, cpu);
- struct desc_struct *gdt = per_cpu(cpu_gdt, cpu);
- struct i386_pda *pda = &per_cpu(_cpu_pda, cpu);
-
- memcpy(gdt, cpu_gdt_table, GDT_SIZE);
- cpu_gdt_descr->address = (unsigned long)gdt;
- cpu_gdt_descr->size = GDT_SIZE - 1;
-
- pack_descriptor((u32 *)&gdt[GDT_ENTRY_PDA].a,
- (u32 *)&gdt[GDT_ENTRY_PDA].b,
- (unsigned long)pda, sizeof(*pda) - 1,
- 0x80 | DESCTYPE_S | 0x2, 0); /* present read-write data segment */
-
- memset(pda, 0, sizeof(*pda));
- pda->_pda = pda;
- pda->cpu_number = cpu;
- pda->pcurrent = idle;
-}
-
-void __cpuinit cpu_set_gdt(int cpu)
-{
- struct Xgt_desc_struct *cpu_gdt_descr = &per_cpu(cpu_gdt_descr, cpu);
-
- load_gdt(cpu_gdt_descr);
- set_kernel_fs();
-}
-
/* Common CPU init for both boot and secondary CPUs */
static void __cpuinit _cpu_init(int cpu, struct task_struct *curr)
{
@@ -740,10 +726,6 @@ void __cpuinit cpu_init(void)
int cpu = smp_processor_id();
struct task_struct *curr = current;

- /* Set up the real GDT and PDA, so we can transition from the
- boot_gdt_table & boot_pda. */
- init_gdt(cpu, curr);
- cpu_set_gdt(cpu);
_cpu_init(cpu, curr);
}

Index: linux/arch/i386/kernel/head.S
===================================================================
--- linux.orig/arch/i386/kernel/head.S
+++ linux/arch/i386/kernel/head.S
@@ -599,7 +599,7 @@ idt_descr:
.word 0 # 32 bit align gdt_desc.address
ENTRY(early_gdt_descr)
.word GDT_ENTRIES*8-1
- .long cpu_gdt_table
+ .long per_cpu__cpu_gdt /* Overwritten for secondary CPUs */

/*
* The boot_gdt_table must mirror the equivalent in setup.S and is
@@ -610,56 +610,3 @@ ENTRY(boot_gdt_table)
.fill GDT_ENTRY_BOOT_CS,8,0
.quad 0x00cf9a000000ffff /* kernel 4GB code at 0x00000000 */
.quad 0x00cf92000000ffff /* kernel 4GB data at 0x00000000 */
-
-/*
- * The Global Descriptor Table contains 32 quadwords, per-CPU.
- */
- .align L1_CACHE_BYTES
-ENTRY(cpu_gdt_table)
- .quad 0x0000000000000000 /* NULL descriptor */
- .quad 0x0000000000000000 /* 0x0b reserved */
- .quad 0x0000000000000000 /* 0x13 reserved */
- .quad 0x0000000000000000 /* 0x1b reserved */
- .quad 0x0000000000000000 /* 0x20 unused */
- .quad 0x0000000000000000 /* 0x28 unused */
- .quad 0x0000000000000000 /* 0x33 TLS entry 1 */
- .quad 0x0000000000000000 /* 0x3b TLS entry 2 */
- .quad 0x0000000000000000 /* 0x43 TLS entry 3 */
- .quad 0x0000000000000000 /* 0x4b reserved */
- .quad 0x0000000000000000 /* 0x53 reserved */
- .quad 0x0000000000000000 /* 0x5b reserved */
-
- .quad 0x00cf9a000000ffff /* 0x60 kernel 4GB code at 0x00000000 */
- .quad 0x00cf92000000ffff /* 0x68 kernel 4GB data at 0x00000000 */
- .quad 0x00cffa000000ffff /* 0x73 user 4GB code at 0x00000000 */
- .quad 0x00cff2000000ffff /* 0x7b user 4GB data at 0x00000000 */
-
- .quad 0x0000000000000000 /* 0x80 TSS descriptor */
- .quad 0x0000000000000000 /* 0x88 LDT descriptor */
-
- /*
- * Segments used for calling PnP BIOS have byte granularity.
- * The code segments and data segments have fixed 64k limits,
- * the transfer segment sizes are set at run time.
- */
- .quad 0x00409a000000ffff /* 0x90 32-bit code */
- .quad 0x00009a000000ffff /* 0x98 16-bit code */
- .quad 0x000092000000ffff /* 0xa0 16-bit data */
- .quad 0x0000920000000000 /* 0xa8 16-bit data */
- .quad 0x0000920000000000 /* 0xb0 16-bit data */
-
- /*
- * The APM segments have byte granularity and their bases
- * are set at run time. All have 64k limits.
- */
- .quad 0x00409a000000ffff /* 0xb8 APM CS code */
- .quad 0x00009a000000ffff /* 0xc0 APM CS 16 code (16 bit) */
- .quad 0x004092000000ffff /* 0xc8 APM DS data */
-
- .quad 0x00c0920000000000 /* 0xd0 - ESPFIX SS */
- .quad 0x00cf92000000ffff /* 0xd8 - PDA */
- .quad 0x0000000000000000 /* 0xe0 - unused */
- .quad 0x0000000000000000 /* 0xe8 - unused */
- .quad 0x0000000000000000 /* 0xf0 - unused */
- .quad 0x0000000000000000 /* 0xf8 - GDT entry 31: double-fault TSS */
-
Index: linux/arch/i386/kernel/smpboot.c
===================================================================
--- linux.orig/arch/i386/kernel/smpboot.c
+++ linux/arch/i386/kernel/smpboot.c
@@ -440,12 +440,6 @@ static void __cpuinit start_secondary(vo
void __devinit initialize_secondary(void)
{
/*
- * switch to the per CPU GDT we already set up
- * in do_boot_cpu()
- */
- cpu_set_gdt(current_thread_info()->cpu);
-
- /*
* We don't actually need to load the full TSS,
* basically just the stack pointer and the eip.
*/
@@ -787,6 +781,32 @@ static inline struct task_struct * alloc
#define alloc_idle_task(cpu) fork_idle(cpu)
#endif

+/* Initialize the CPU's GDT. This is either the boot CPU doing itself
+ (still using the master per-cpu area), or a CPU doing it for a
+ secondary which will soon come up. */
+static __cpuinit void init_gdt(int cpu, struct task_struct *idle)
+{
+ struct Xgt_desc_struct *cpu_gdt_descr = &per_cpu(cpu_gdt_descr, cpu);
+ struct desc_struct *gdt = per_cpu(cpu_gdt, cpu);
+ struct i386_pda *pda = &per_cpu(_cpu_pda, cpu);
+
+ cpu_gdt_descr->address = (unsigned long)gdt;
+ cpu_gdt_descr->size = GDT_SIZE - 1;
+
+ pack_descriptor((u32 *)&gdt[GDT_ENTRY_PDA].a,
+ (u32 *)&gdt[GDT_ENTRY_PDA].b,
+ (unsigned long)pda, sizeof(*pda) - 1,
+ 0x80 | DESCTYPE_S | 0x2, 0); /* present read-write data segment */
+
+ memset(pda, 0, sizeof(*pda));
+ pda->_pda = pda;
+ pda->cpu_number = cpu;
+ pda->pcurrent = idle;
+}
+
+/* Defined in head.S */
+extern struct Xgt_desc_struct early_gdt_descr;
+
static int __cpuinit do_boot_cpu(int apicid, int cpu)
/*
* NOTE - on most systems this is a PHYSICAL apic ID, but on multiquad
@@ -809,6 +829,8 @@ static int __cpuinit do_boot_cpu(int api
panic("failed fork for CPU %d", cpu);

init_gdt(cpu, idle);
+ early_gdt_descr.address = (unsigned long)get_cpu_gdt_table(cpu);
+ start_pda = cpu_pda(cpu);

idle->thread.eip = (unsigned long) start_secondary;
/* start_eip had better be page-aligned! */
@@ -1161,13 +1183,26 @@ void __init smp_prepare_cpus(unsigned in
smp_boot_cpus(max_cpus);
}

-void __devinit smp_prepare_boot_cpu(void)
+/* Current gdt points %fs at the "master" per-cpu area: after this,
+ * it's on the real one. */
+static inline void switch_to_new_gdt(void)
{
- cpu_set(smp_processor_id(), cpu_online_map);
- cpu_set(smp_processor_id(), cpu_callout_map);
- cpu_set(smp_processor_id(), cpu_present_map);
- cpu_set(smp_processor_id(), cpu_possible_map);
- per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE;
+ load_gdt(&per_cpu(cpu_gdt_descr, smp_processor_id()));
+ asm volatile ("mov %0, %%fs" : : "r" (__KERNEL_PDA) : "memory");
+}
+
+void __init smp_prepare_boot_cpu(void)
+{
+ unsigned int cpu = smp_processor_id();
+
+ init_gdt(cpu, current);
+ switch_to_new_gdt();
+
+ cpu_set(cpu, cpu_online_map);
+ cpu_set(cpu, cpu_callout_map);
+ cpu_set(cpu, cpu_present_map);
+ cpu_set(cpu, cpu_possible_map);
+ __get_cpu_var(cpu_state) = CPU_ONLINE;
}

#ifdef CONFIG_HOTPLUG_CPU
Index: linux/arch/i386/mach-voyager/voyager_smp.c
===================================================================
--- linux.orig/arch/i386/mach-voyager/voyager_smp.c
+++ linux/arch/i386/mach-voyager/voyager_smp.c
@@ -765,12 +765,6 @@ initialize_secondary(void)
#endif

/*
- * switch to the per CPU GDT we already set up
- * in do_boot_cpu()
- */
- cpu_set_gdt(current_thread_info()->cpu);
-
- /*
* We don't actually need to load the full TSS,
* basically just the stack pointer and the eip.
*/
Index: linux/include/asm-i386/desc.h
===================================================================
--- linux.orig/include/asm-i386/desc.h
+++ linux/include/asm-i386/desc.h
@@ -12,8 +12,6 @@

#include <asm/mmu.h>

-extern struct desc_struct cpu_gdt_table[GDT_ENTRIES];
-
struct Xgt_desc_struct {
unsigned short size;
unsigned long address __attribute__((packed));
Index: linux/include/asm-i386/processor.h
===================================================================
--- linux.orig/include/asm-i386/processor.h
+++ linux/include/asm-i386/processor.h
@@ -743,7 +743,6 @@ extern unsigned long boot_option_idle_ov
extern void enable_sep_cpu(void);
extern int sysenter_setup(void);

-extern void init_gdt(int cpu, struct task_struct *idle);
extern void cpu_set_gdt(int);
extern void secondary_cpu_init(void);

-
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