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Subject[PATCH 01/02] kexec: Move segment code to assembly file (i386)
kexec: Move segment code to assembly file (i386)

This patch moves the idt, gdt, and segment handling code from machine_kexec.c
to relocate_kernel.S. The main reason behind this move is to avoid code
duplication in the Xen hypervisor. With this patch all code required to kexec
is put on the control page.

Signed-off-by: Magnus Damm <magnus@valinux.co.jp>
---

Applies to 2.6.19.

arch/i386/kernel/machine_kexec.c | 59 ------------------------------------
arch/i386/kernel/relocate_kernel.S | 58 ++++++++++++++++++++++++++++++++---
2 files changed, 53 insertions(+), 64 deletions(-)

--- 0001/arch/i386/kernel/machine_kexec.c
+++ work/arch/i386/kernel/machine_kexec.c 2006-12-05 17:24:10.000000000 +0900
@@ -29,48 +29,6 @@ static u32 kexec_pmd1[1024] PAGE_ALIGNED
static u32 kexec_pte0[1024] PAGE_ALIGNED;
static u32 kexec_pte1[1024] PAGE_ALIGNED;

-static void set_idt(void *newidt, __u16 limit)
-{
- struct Xgt_desc_struct curidt;
-
- /* ia32 supports unaliged loads & stores */
- curidt.size = limit;
- curidt.address = (unsigned long)newidt;
-
- load_idt(&curidt);
-};
-
-
-static void set_gdt(void *newgdt, __u16 limit)
-{
- struct Xgt_desc_struct curgdt;
-
- /* ia32 supports unaligned loads & stores */
- curgdt.size = limit;
- curgdt.address = (unsigned long)newgdt;
-
- load_gdt(&curgdt);
-};
-
-static void load_segments(void)
-{
-#define __STR(X) #X
-#define STR(X) __STR(X)
-
- __asm__ __volatile__ (
- "\tljmp $"STR(__KERNEL_CS)",$1f\n"
- "\t1:\n"
- "\tmovl $"STR(__KERNEL_DS)",%%eax\n"
- "\tmovl %%eax,%%ds\n"
- "\tmovl %%eax,%%es\n"
- "\tmovl %%eax,%%fs\n"
- "\tmovl %%eax,%%gs\n"
- "\tmovl %%eax,%%ss\n"
- ::: "eax", "memory");
-#undef STR
-#undef __STR
-}
-
/*
* A architecture hook called to validate the
* proposed image and prepare the control pages
@@ -127,23 +85,6 @@ NORET_TYPE void machine_kexec(struct kim
page_list[PA_PTE_1] = __pa(kexec_pte1);
page_list[VA_PTE_1] = (unsigned long)kexec_pte1;

- /* The segment registers are funny things, they have both a
- * visible and an invisible part. Whenever the visible part is
- * set to a specific selector, the invisible part is loaded
- * with from a table in memory. At no other time is the
- * descriptor table in memory accessed.
- *
- * I take advantage of this here by force loading the
- * segments, before I zap the gdt with an invalid value.
- */
- load_segments();
- /* The gdt & idt are now invalid.
- * If you want to load them you must set up your own idt & gdt.
- */
- set_gdt(phys_to_virt(0),0);
- set_idt(phys_to_virt(0),0);
-
- /* now call it */
relocate_kernel((unsigned long)image->head, (unsigned long)page_list,
image->start, cpu_has_pae);
}
--- 0001/arch/i386/kernel/relocate_kernel.S
+++ work/arch/i386/kernel/relocate_kernel.S 2006-12-05 17:24:10.000000000 +0900
@@ -154,14 +154,45 @@ relocate_new_kernel:
movl PTR(PA_PGD)(%ebp), %eax
movl %eax, %cr3

+ /* setup idt */
+ movl %edi, %eax
+ addl $(idt_48 - relocate_kernel), %eax
+ lidtl (%eax)
+
+ /* setup gdt */
+ movl %edi, %eax
+ addl $(gdt - relocate_kernel), %eax
+ movl %edi, %esi
+ addl $((gdt_48 - relocate_kernel) + 2), %esi
+ movl %eax, (%esi)
+
+ movl %edi, %eax
+ addl $(gdt_48 - relocate_kernel), %eax
+ lgdtl (%eax)
+
+ /* setup data segment registers */
+ mov $(gdt_ds - gdt), %eax
+ mov %eax, %ds
+ mov %eax, %es
+ mov %eax, %fs
+ mov %eax, %gs
+ mov %eax, %ss
+
/* setup a new stack at the end of the physical control page */
lea 4096(%edi), %esp

- /* jump to identity mapped page */
- movl %edi, %eax
- addl $(identity_mapped - relocate_kernel), %eax
- pushl %eax
- ret
+ /* load new code segment and jump to identity mapped page */
+ movl %edi, %esi
+ xorl %eax, %eax
+ pushl %eax
+ pushl %esi
+ pushl %eax
+ movl $(gdt_cs - gdt), %eax
+ pushl %eax
+ movl %edi, %eax
+ addl $(identity_mapped - relocate_kernel),%eax
+ pushl %eax
+ iretl

identity_mapped:
/* store the start address on the stack */
@@ -250,3 +281,20 @@ identity_mapped:
xorl %edi, %edi
xorl %ebp, %ebp
ret
+
+ .align 16
+gdt:
+ .quad 0x0000000000000000 /* NULL descriptor */
+gdt_cs:
+ .quad 0x00cf9a000000ffff /* kernel 4GB code at 0x00000000 */
+gdt_ds:
+ .quad 0x00cf92000000ffff /* kernel 4GB data at 0x00000000 */
+gdt_end:
+
+gdt_48:
+ .word gdt_end - gdt - 1 /* limit */
+ .long 0 /* base - filled in by code above */
+
+idt_48:
+ .word 0 /* limit */
+ .long 0 /* base */
-
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