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[PATCH] i386: Use %gs as the PDA base-segment in the kernel

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This patch is the meat of the PDA change.  This patch makes several related
changes:

1: Most significantly, %gs is now used in the kernel.  This means that on
   entry, the old value of %gs is saved away, and it is reloaded with
   __KERNEL_PDA.

2: entry.S constructs the stack in the shape of struct pt_regs, and this
   is passed around the kernel so that the process's saved register
   state can be accessed.

   Unfortunately struct pt_regs doesn't currently have space for %gs
   (or %fs). This patch extends pt_regs to add space for gs (no space
   is allocated for %fs, since it won't be used, and it would just
   complicate the code in entry.S to work around the space).

3: Because %gs is now saved on the stack like %ds, %es and the integer
   registers, there are a number of places where it no longer needs to
   be handled specially; namely context switch, and saving/restoring the
   register state in a signal context.

4: And since kernel threads run in kernel space and call normal kernel
   code, they need to be created with their %gs == __KERNEL_PDA.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Chuck Ebbert <76306.1226@compuserve.com>
Cc: Zachary Amsden <zach@vmware.com>
Cc: Jan Beulich <jbeulich@novell.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
This commit is contained in:
Jeremy Fitzhardinge
2006-12-07 02:14:02 +01:00
committed by Andi Kleen
parent 6211119580
commit f95d47caae
10 changed files with 117 additions and 50 deletions
Download Patch File Download Diff File Expand all files Collapse all files

21
arch/i386/kernel/cpu/common.c
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@@ -593,6 +593,14 @@ void __init early_cpu_init(void)
#endif
}
/* Make sure %gs is initialized properly in idle threads */
struct pt_regs * __devinit idle_regs(struct pt_regs *regs)
{
memset(regs, 0, sizeof(struct pt_regs));
regs->xgs = __KERNEL_PDA;
return regs;
}
__cpuinit int alloc_gdt(int cpu)
{
struct Xgt_desc_struct *cpu_gdt_descr = &per_cpu(cpu_gdt_descr, cpu);
@@ -644,6 +652,14 @@ struct i386_pda boot_pda = {
._pda = &boot_pda,
};
static inline void set_kernel_gs(void)
{
/* Set %gs 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, %%gs" : : "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)
@@ -693,6 +709,7 @@ static void __cpuinit _cpu_init(int cpu, struct task_struct *curr)
the boot CPU, this will transition from the boot gdt+pda to
the real ones). */
load_gdt(cpu_gdt_descr);
set_kernel_gs();
if (cpu_test_and_set(cpu, cpu_initialized)) {
printk(KERN_WARNING "CPU#%d already initialized!\n", cpu);
@@ -731,8 +748,8 @@ static void __cpuinit _cpu_init(int cpu, struct task_struct *curr)
__set_tss_desc(cpu, GDT_ENTRY_DOUBLEFAULT_TSS, &doublefault_tss);
#endif
/* Clear %fs and %gs. */
asm volatile ("movl %0, %%fs; movl %0, %%gs" : : "r" (0));
/* Clear %fs. */
asm volatile ("mov %0, %%fs" : : "r" (0));
/* Clear all 6 debug registers: */
set_debugreg(0, 0);