[patch 3/6] Page-align the GDT

Jeremy Fitzhardinge
2007-03-31T04:53:46Z

[-- Attachment #1: i386-gdt-cleanups-page-align-the-gdt.patch --]
[-- Type: text/plain, Size: 3467 bytes --]

Xen wants a dedicated page for the GDT. I believe VMI likes it too.
lguest, KVM and native don't care.

Simple transformation to page-aligned "struct gdt_page".

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Jeremy Fitzhardinge <jeremy@xensource.com>

---
arch/i386/kernel/cpu/common.c | 6 +++---
arch/i386/kernel/entry.S | 2 +-
arch/i386/kernel/head.S | 2 +-
arch/i386/kernel/traps.c | 2 +-
include/asm-i386/desc.h | 9 +++++++--
5 files changed, 13 insertions(+), 8 deletions(-)

===================================================================
--- a/arch/i386/kernel/cpu/common.c
+++ b/arch/i386/kernel/cpu/common.c
@@ -22,7 +22,7 @@

#include "cpu.h"

-DEFINE_PER_CPU(struct desc_struct, cpu_gdt[GDT_ENTRIES]) = {
+DEFINE_PER_CPU(struct gdt_page, gdt_page) = { .gdt = {
[GDT_ENTRY_KERNEL_CS] = { 0x0000ffff, 0x00cf9a00 },
[GDT_ENTRY_KERNEL_DS] = { 0x0000ffff, 0x00cf9200 },
[GDT_ENTRY_DEFAULT_USER_CS] = { 0x0000ffff, 0x00cffa00 },
@@ -48,8 +48,8 @@ DEFINE_PER_CPU(struct desc_struct, cpu_g

[GDT_ENTRY_ESPFIX_SS] = { 0x00000000, 0x00c09200 },
[GDT_ENTRY_PDA] = { 0x00000000, 0x00c09200 }, /* set in setup_pda */
-};
-EXPORT_PER_CPU_SYMBOL_GPL(cpu_gdt);
+} };
+EXPORT_PER_CPU_SYMBOL_GPL(gdt_page);

DEFINE_PER_CPU(struct i386_pda, _cpu_pda) = {
._pda = &per_cpu___cpu_pda,
===================================================================
--- a/arch/i386/kernel/entry.S
+++ b/arch/i386/kernel/entry.S
@@ -558,7 +558,7 @@ END(syscall_badsys)
#define FIXUP_ESPFIX_STACK \
/* since we are on a wrong stack, we cant make it a C code :( */ \
movl %fs:PDA_cpu, %ebx; \
- PER_CPU(cpu_gdt, %ebx); \
+ PER_CPU(gdt_page, %ebx); \
GET_DESC_BASE(GDT_ENTRY_ESPFIX_SS, %ebx, %eax, %ax, %al, %ah); \
addl %esp, %eax; \
pushl $__KERNEL_DS; \
===================================================================
--- a/arch/i386/kernel/head.S
+++ b/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 per_cpu__cpu_gdt /* Overwritten for secondary CPUs */
+ .long per_cpu__gdt_page /* Overwritten for secondary CPUs */

/*
* The boot_gdt_table must mirror the equivalent in setup.S and is
===================================================================
--- a/arch/i386/kernel/traps.c
+++ b/arch/i386/kernel/traps.c
@@ -1037,7 +1037,7 @@ fastcall unsigned long patch_espfix_desc
fastcall unsigned long patch_espfix_desc(unsigned long uesp,
unsigned long kesp)
{
- struct desc_struct *gdt = __get_cpu_var(cpu_gdt);
+ struct desc_struct *gdt = __get_cpu_var(gdt_page).gdt;
unsigned long base = (kesp - uesp) & -THREAD_SIZE;
unsigned long new_kesp = kesp - base;
unsigned long lim_pages = (new_kesp | (THREAD_SIZE - 1)) >> PAGE_SHIFT;
===================================================================
--- a/include/asm-i386/desc.h
+++ b/include/asm-i386/desc.h
@@ -18,10 +18,15 @@ struct Xgt_desc_struct {
unsigned short pad;
} __attribute__ ((packed));

-DECLARE_PER_CPU(struct desc_struct, cpu_gdt[GDT_ENTRIES]);
+struct gdt_page
+{
+ struct desc_struct gdt[GDT_ENTRIES];
+} __attribute__((aligned(PAGE_SIZE)));
+DECLARE_PER_CPU(struct gdt_page, gdt_page);
+
static inline struct desc_struct *get_cpu_gdt_table(unsigned int cpu)
{
- return per_cpu(cpu_gdt, cpu);
+ return per_cpu(gdt_page, cpu).gdt;
}

extern struct Xgt_desc_struct idt_descr;

--