[PATCH] i386: Use per-cpu variables for GDT, PDA

Allocating PDA and GDT at boot is a pain.  Using simple per-cpu variables adds
happiness (although we need the GDT page-aligned for Xen, which we do in a
followup patch).

[akpm@linux-foundation.org: build fix]
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>

3 files changed, 15 insertions, 110 deletions

diff --git a/arch/i386/kernel/cpu/common.c b/arch/i386/kernel/cpu/common.c
index dcbbd0a8bfc2..2335f4464ead 100644
--- a/arch/i386/kernel/cpu/common.c
+++ b/arch/i386/kernel/cpu/common.c
@@ -25,8 +25,10 @@
 DEFINE_PER_CPU(struct Xgt_desc_struct, cpu_gdt_descr);
 EXPORT_PER_CPU_SYMBOL(cpu_gdt_descr);
 
-struct i386_pda *_cpu_pda[NR_CPUS] __read_mostly;
-EXPORT_SYMBOL(_cpu_pda);
+DEFINE_PER_CPU(struct desc_struct, cpu_gdt[GDT_ENTRIES]);
+
+DEFINE_PER_CPU(struct i386_pda, _cpu_pda);
+EXPORT_PER_CPU_SYMBOL(_cpu_pda);
 
 static int cachesize_override __cpuinitdata = -1;
 static int disable_x86_fxsr __cpuinitdata;
@@ -609,52 +611,6 @@ struct pt_regs * __devinit idle_regs(struct pt_regs *regs)
         return regs;
 }
 
-static __cpuinit int alloc_gdt(int cpu)
-{
-        struct Xgt_desc_struct *cpu_gdt_descr = &per_cpu(cpu_gdt_descr, cpu);
-        struct desc_struct *gdt;
-        struct i386_pda *pda;
-
-        gdt = (struct desc_struct *)cpu_gdt_descr->address;
-        pda = cpu_pda(cpu);
-
-        /*
-         * This is a horrible hack to allocate the GDT.  The problem
-         * is that cpu_init() is called really early for the boot CPU
-         * (and hence needs bootmem) but much later for the secondary
-         * CPUs, when bootmem will have gone away
-         */
-        if (NODE_DATA(0)->bdata->node_bootmem_map) {
-                BUG_ON(gdt != NULL || pda != NULL);
-
-                gdt = alloc_bootmem_pages(PAGE_SIZE);
-                pda = alloc_bootmem(sizeof(*pda));
-                /* alloc_bootmem(_pages) panics on failure, so no check */
-
-                memset(gdt, 0, PAGE_SIZE);
-                memset(pda, 0, sizeof(*pda));
-        } else {
-                /* GDT and PDA might already have been allocated if
-                   this is a CPU hotplug re-insertion. */
-                if (gdt == NULL)
-                        gdt = (struct desc_struct *)get_zeroed_page(GFP_KERNEL);
-
-                if (pda == NULL)
-                        pda = kmalloc_node(sizeof(*pda), GFP_KERNEL, cpu_to_node(cpu));
-
-                if (unlikely(!gdt || !pda)) {
-                        free_pages((unsigned long)gdt, 0);
-                        kfree(pda);
-                        return 0;
-                }
-        }
-
-        cpu_gdt_descr->address = (unsigned long)gdt;
-        cpu_pda(cpu) = pda;
-
-        return 1;
-}
-
 /* Initial PDA used by boot CPU */
 struct i386_pda boot_pda = {
         ._pda = &boot_pda,
@@ -670,31 +626,17 @@ static inline void set_kernel_fs(void)
         asm volatile ("mov %0, %%fs" : : "r" (__KERNEL_PDA) : "memory");
 }
 
-/* Initialize the CPU's GDT and PDA.  The boot CPU does this for
-   itself, but secondaries find this done for them. */
-__cpuinit int init_gdt(int cpu, struct task_struct *idle)
+/* 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;
-        struct i386_pda *pda;
-
-        /* For non-boot CPUs, the GDT and PDA should already have been
-           allocated. */
-        if (!alloc_gdt(cpu)) {
-                printk(KERN_CRIT "CPU%d failed to allocate GDT or PDA\n", cpu);
-                return 0;
-        }
+        struct desc_struct *gdt = per_cpu(cpu_gdt, cpu);
+        struct i386_pda *pda = &per_cpu(_cpu_pda, cpu);
 
-        gdt = (struct desc_struct *)cpu_gdt_descr->address;
-        pda = cpu_pda(cpu);
-
-        BUG_ON(gdt == NULL || pda == NULL);
-
-        /*
-         * Initialize the per-CPU GDT with the boot GDT,
-         * and set up the GDT descriptor:
-         */
         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,
@@ -706,17 +648,12 @@ __cpuinit int init_gdt(int cpu, struct task_struct *idle)
         pda->_pda = pda;
         pda->cpu_number = cpu;
         pda->pcurrent = idle;
-
-        return 1;
 }
 
 void __cpuinit cpu_set_gdt(int cpu)
 {
         struct Xgt_desc_struct *cpu_gdt_descr = &per_cpu(cpu_gdt_descr, cpu);
 
-        /* Reinit these anyway, even if they've already been done (on
-           the boot CPU, this will transition from the boot gdt+pda to
-           the real ones). */
         load_gdt(cpu_gdt_descr);
         set_kernel_fs();
 }
@@ -804,13 +741,8 @@ void __cpuinit cpu_init(void)
         struct task_struct *curr = current;
 
         /* Set up the real GDT and PDA, so we can transition from the
-           boot versions. */
-        if (!init_gdt(cpu, curr)) {
-                /* failed to allocate something; not much we can do... */
-                for (;;)
-                        local_irq_enable();
-        }
-
+           boot_gdt_table & boot_pda. */
+        init_gdt(cpu, curr);
         cpu_set_gdt(cpu);
         _cpu_init(cpu, curr);
 }
diff --git a/arch/i386/kernel/smpboot.c b/arch/i386/kernel/smpboot.c
index 7b14e88b555f..b36a5f174cc9 100644
--- a/arch/i386/kernel/smpboot.c
+++ b/arch/i386/kernel/smpboot.c
@@ -808,13 +808,7 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu)
         if (IS_ERR(idle))
                 panic("failed fork for CPU %d", cpu);
 
-        /* Pre-allocate and initialize the CPU's GDT and PDA so it
-           doesn't have to do any memory allocation during the
-           delicate CPU-bringup phase. */
-        if (!init_gdt(cpu, idle)) {
-                printk(KERN_INFO "Couldn't allocate GDT/PDA for CPU %d\n", cpu);
-                return -1;      /* ? */
-        }
+        init_gdt(cpu, idle);
 
         idle->thread.eip = (unsigned long) start_secondary;
         /* start_eip had better be page-aligned! */
@@ -940,7 +934,6 @@ static int __cpuinit __smp_prepare_cpu(int cpu)
         DECLARE_COMPLETION_ONSTACK(done);
         struct warm_boot_cpu_info info;
         int     apicid, ret;
-        struct Xgt_desc_struct *cpu_gdt_descr = &per_cpu(cpu_gdt_descr, cpu);
 
         apicid = x86_cpu_to_apicid[cpu];
         if (apicid == BAD_APICID) {
@@ -948,18 +941,6 @@ static int __cpuinit __smp_prepare_cpu(int cpu)
                 goto exit;
         }
 
-        /*
-         * the CPU isn't initialized at boot time, allocate gdt table here.
-         * cpu_init will initialize it
-         */
-        if (!cpu_gdt_descr->address) {
-                cpu_gdt_descr->address = get_zeroed_page(GFP_KERNEL);
-                if (!cpu_gdt_descr->address)
-                        printk(KERN_CRIT "CPU%d failed to allocate GDT\n", cpu);
-                        ret = -ENOMEM;
-                        goto exit;
-        }
-
         info.complete = &done;
         info.apicid = apicid;
         info.cpu = cpu;
diff --git a/arch/i386/mach-voyager/voyager_smp.c b/arch/i386/mach-voyager/voyager_smp.c
index 74aeedf277f4..15d8132d4f5e 100644
--- a/arch/i386/mach-voyager/voyager_smp.c
+++ b/arch/i386/mach-voyager/voyager_smp.c
@@ -580,15 +580,7 @@ do_boot_cpu(__u8 cpu)
         /* init_tasks (in sched.c) is indexed logically */
         stack_start.esp = (void *) idle->thread.esp;
 
-        /* Pre-allocate and initialize the CPU's GDT and PDA so it
-           doesn't have to do any memory allocation during the
-           delicate CPU-bringup phase. */
-        if (!init_gdt(cpu, idle)) {
-                printk(KERN_INFO "Couldn't allocate GDT/PDA for CPU %d\n", cpu);
-                cpucount--;
-                return;
-        }
-
+        init_gdt(cpu, idle);
         irq_ctx_init(cpu);
 
         /* Note: Don't modify initial ss override */