[PATCH] x86: fix broken SMP boot sequence

Recent GDT changes broke the SMP boot sequence if the booting CPU is
numbered anything other than zero.  There's also a subtle source of error
in that the boot time CPU now uses cpu_gdt_table (which is actually the GDT
for booting CPUs in head.S).  This patch fixes both problems by making GDT
descriptors themselves allocated from a per_cpu area and switching to them
in cpu_init(), which now means that cpu_gdt_table is exclusively used for
booting CPUs again.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
Cc: Zachary Amsden <zach@vmware.com>
Cc: Matt Tolentino <metolent@snoqualmie.dp.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

6 files changed, 39 insertions, 21 deletions

diff --git a/arch/i386/kernel/cpu/common.c b/arch/i386/kernel/cpu/common.c
index 7eb9213734a3..4ecd4b326ded 100644
--- a/arch/i386/kernel/cpu/common.c
+++ b/arch/i386/kernel/cpu/common.c
@@ -4,6 +4,7 @@
 #include <linux/smp.h>
 #include <linux/module.h>
 #include <linux/percpu.h>
+#include <linux/bootmem.h>
 #include <asm/semaphore.h>
 #include <asm/processor.h>
 #include <asm/i387.h>
@@ -18,6 +19,9 @@
 
 #include "cpu.h"
 
+DEFINE_PER_CPU(struct Xgt_desc_struct, cpu_gdt_descr);
+EXPORT_PER_CPU_SYMBOL(cpu_gdt_descr);
+
 DEFINE_PER_CPU(unsigned char, cpu_16bit_stack[CPU_16BIT_STACK_SIZE]);
 EXPORT_PER_CPU_SYMBOL(cpu_16bit_stack);
 
@@ -571,8 +575,9 @@ void __devinit cpu_init(void)
         int cpu = smp_processor_id();
         struct tss_struct * t = &per_cpu(init_tss, cpu);
         struct thread_struct *thread = &current->thread;
-        struct desc_struct *gdt = get_cpu_gdt_table(cpu);
+        struct desc_struct *gdt;
         __u32 stk16_off = (__u32)&per_cpu(cpu_16bit_stack, cpu);
+        struct Xgt_desc_struct *cpu_gdt_descr = &per_cpu(cpu_gdt_descr, cpu);
 
         if (cpu_test_and_set(cpu, cpu_initialized)) {
                 printk(KERN_WARNING "CPU#%d already initialized!\n", cpu);
@@ -590,6 +595,25 @@ void __devinit cpu_init(void)
         }
 
         /*
+         * 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) {
+                gdt = (struct desc_struct *)alloc_bootmem_pages(PAGE_SIZE);
+                /* alloc_bootmem_pages panics on failure, so no check */
+                memset(gdt, 0, PAGE_SIZE);
+        } else {
+                gdt = (struct desc_struct *)get_zeroed_page(GFP_KERNEL);
+                if (unlikely(!gdt)) {
+                        printk(KERN_CRIT "CPU%d failed to allocate GDT\n", cpu);
+                        for (;;)
+                                local_irq_enable();
+                }
+        }
+
+        /*
          * Initialize the per-CPU GDT with the boot GDT,
          * and set up the GDT descriptor:
          */
@@ -601,10 +625,10 @@ void __devinit cpu_init(void)
                 ((((__u64)stk16_off) << 32) & 0xff00000000000000ULL) |
                 (CPU_16BIT_STACK_SIZE - 1);
 
-        cpu_gdt_descr[cpu].size = GDT_SIZE - 1;
-        cpu_gdt_descr[cpu].address = (unsigned long)gdt;
+        cpu_gdt_descr->size = GDT_SIZE - 1;
+        cpu_gdt_descr->address = (unsigned long)gdt;
 
-        load_gdt(&cpu_gdt_descr[cpu]);
+        load_gdt(cpu_gdt_descr);
         load_idt(&idt_descr);
 
         /*
diff --git a/arch/i386/kernel/efi.c b/arch/i386/kernel/efi.c
index ecad519fd395..e3e42fd62401 100644
--- a/arch/i386/kernel/efi.c
+++ b/arch/i386/kernel/efi.c
@@ -103,17 +103,19 @@ static void efi_call_phys_prelog(void)
          */
         local_flush_tlb();
 
-        cpu_gdt_descr[0].address = __pa(cpu_gdt_descr[0].address);
-        load_gdt((struct Xgt_desc_struct *) __pa(&cpu_gdt_descr[0]));
+        per_cpu(cpu_gdt_descr, 0).address =
+                                 __pa(per_cpu(cpu_gdt_descr, 0).address);
+        load_gdt((struct Xgt_desc_struct *)__pa(&per_cpu(cpu_gdt_descr, 0)));
 }
 
 static void efi_call_phys_epilog(void)
 {
         unsigned long cr4;
 
-        cpu_gdt_descr[0].address =
-                (unsigned long) __va(cpu_gdt_descr[0].address);
-        load_gdt(&cpu_gdt_descr[0]);
+        per_cpu(cpu_gdt_descr, 0).address =
+                        (unsigned long)__va(per_cpu(cpu_gdt_descr, 0).address);
+        load_gdt((struct Xgt_desc_struct *)__va(&per_cpu(cpu_gdt_descr, 0)));
+
         cr4 = read_cr4();
 
         if (cr4 & X86_CR4_PSE) {
diff --git a/arch/i386/kernel/head.S b/arch/i386/kernel/head.S
index 2bee6499edd9..e0b7c632efbc 100644
--- a/arch/i386/kernel/head.S
+++ b/arch/i386/kernel/head.S
@@ -534,5 +534,3 @@ ENTRY(cpu_gdt_table)
         .quad 0x0000000000000000        /* 0xf0 - unused */
         .quad 0x0000000000000000        /* 0xf8 - GDT entry 31: double-fault TSS */
 
-        /* Be sure this is zeroed to avoid false validations in Xen */
-        .fill PAGE_SIZE_asm / 8 - GDT_ENTRIES,8,0
diff --git a/arch/i386/kernel/i386_ksyms.c b/arch/i386/kernel/i386_ksyms.c
index 3999bec50c33..055325056a74 100644
--- a/arch/i386/kernel/i386_ksyms.c
+++ b/arch/i386/kernel/i386_ksyms.c
@@ -3,8 +3,6 @@
 #include <asm/checksum.h>
 #include <asm/desc.h>
 
-EXPORT_SYMBOL_GPL(cpu_gdt_descr);
-
 EXPORT_SYMBOL(__down_failed);
 EXPORT_SYMBOL(__down_failed_interruptible);
 EXPORT_SYMBOL(__down_failed_trylock);
diff --git a/arch/i386/kernel/smpboot.c b/arch/i386/kernel/smpboot.c
index fb00ab7b7612..eba7f53f8b4a 100644
--- a/arch/i386/kernel/smpboot.c
+++ b/arch/i386/kernel/smpboot.c
@@ -898,12 +898,6 @@ static int __devinit do_boot_cpu(int apicid, int cpu)
         unsigned long start_eip;
         unsigned short nmi_high = 0, nmi_low = 0;
 
-        if (!cpu_gdt_descr[cpu].address &&
-            !(cpu_gdt_descr[cpu].address = get_zeroed_page(GFP_KERNEL))) {
-                printk("Failed to allocate GDT for CPU %d\n", cpu);
-                return 1;
-        }
-
         ++cpucount;
 
         /*
diff --git a/include/asm-i386/desc.h b/include/asm-i386/desc.h
index 494e73bca095..89b8b82c82b3 100644
--- a/include/asm-i386/desc.h
+++ b/include/asm-i386/desc.h
@@ -24,11 +24,13 @@ struct Xgt_desc_struct {
         unsigned short pad;
 } __attribute__ ((packed));
 
-extern struct Xgt_desc_struct idt_descr, cpu_gdt_descr[NR_CPUS];
+extern struct Xgt_desc_struct idt_descr;
+DECLARE_PER_CPU(struct Xgt_desc_struct, cpu_gdt_descr);
+
 
 static inline struct desc_struct *get_cpu_gdt_table(unsigned int cpu)
 {
-        return ((struct desc_struct *)cpu_gdt_descr[cpu].address);
+        return (struct desc_struct *)per_cpu(cpu_gdt_descr, cpu).address;
 }
 
 #define load_TR_desc() __asm__ __volatile__("ltr %w0"::"q" (GDT_ENTRY_TSS*8))