[RFC] [PATCH 12/16] x86_64: Remove the identity mapping as early as possible
From: Vivek Goyal
Date: Mon Nov 13 2006 - 11:54:08 EST
With the rewrite of the SMP trampoline and the early page
allocator there is nothing that needs identity mapped pages,
once we start executing C code.
So add zap_identity_mappings into head64.c and remove
zap_low_mappings() from much later in the code. The functions
are subtly different thus the name change.
This also kills boot_level4_pgt which was from an earlier
attempt to move the identity mappings as early as possible,
and is now no longer needed. Essentially I have replaced
boot_level4_pgt with trampoline_level4_pgt in trampoline.S
Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
---
arch/x86_64/kernel/head.S | 39 ++++++++++++++-------------------------
arch/x86_64/kernel/head64.c | 16 ++++++++++------
arch/x86_64/kernel/setup.c | 2 --
arch/x86_64/kernel/setup64.c | 1 -
arch/x86_64/mm/init.c | 24 ------------------------
include/asm-x86_64/pgtable.h | 1 -
include/asm-x86_64/proto.h | 2 --
7 files changed, 24 insertions(+), 61 deletions(-)
diff -puN arch/x86_64/kernel/head64.c~x86_64-Remove-the-identity-mapping-as-early-as-possible arch/x86_64/kernel/head64.c
--- linux-2.6.19-rc5-reloc/arch/x86_64/kernel/head64.c~x86_64-Remove-the-identity-mapping-as-early-as-possible 2006-11-09 23:04:38.000000000 -0500
+++ linux-2.6.19-rc5-reloc-root/arch/x86_64/kernel/head64.c 2006-11-09 23:04:38.000000000 -0500
@@ -18,8 +18,16 @@
#include <asm/setup.h>
#include <asm/desc.h>
#include <asm/pgtable.h>
+#include <asm/tlbflush.h>
#include <asm/sections.h>
+static void __init zap_identity_mappings(void)
+{
+ pgd_t *pgd = pgd_offset_k(0UL);
+ pgd_clear(pgd);
+ __flush_tlb();
+}
+
/* Don't add a printk in there. printk relies on the PDA which is not initialized
yet. */
static void __init clear_bss(void)
@@ -56,6 +64,8 @@ void __init x86_64_start_kernel(char * r
{
int i;
+ /* Make NULL pointers segfault */
+ zap_identity_mappings();
for (i = 0; i < 256; i++)
set_intr_gate(i, early_idt_handler);
asm volatile("lidt %0" :: "m" (idt_descr));
@@ -63,12 +73,6 @@ void __init x86_64_start_kernel(char * r
early_printk("Kernel alive\n");
- /*
- * switch to init_level4_pgt from boot_level4_pgt
- */
- memcpy(init_level4_pgt, boot_level4_pgt, PTRS_PER_PGD*sizeof(pgd_t));
- asm volatile("movq %0,%%cr3" :: "r" (__pa_symbol(&init_level4_pgt)));
-
for (i = 0; i < NR_CPUS; i++)
cpu_pda(i) = &boot_cpu_pda[i];
diff -puN arch/x86_64/kernel/head.S~x86_64-Remove-the-identity-mapping-as-early-as-possible arch/x86_64/kernel/head.S
--- linux-2.6.19-rc5-reloc/arch/x86_64/kernel/head.S~x86_64-Remove-the-identity-mapping-as-early-as-possible 2006-11-09 23:04:38.000000000 -0500
+++ linux-2.6.19-rc5-reloc-root/arch/x86_64/kernel/head.S 2006-11-09 23:04:38.000000000 -0500
@@ -71,7 +71,7 @@ startup_32:
movl %eax, %cr4
/* Setup early boot stage 4 level pagetables */
- movl $(boot_level4_pgt - __START_KERNEL_map), %eax
+ movl $(init_level4_pgt - __START_KERNEL_map), %eax
movl %eax, %cr3
/* Setup EFER (Extended Feature Enable Register) */
@@ -115,7 +115,7 @@ ENTRY(secondary_startup_64)
movq %rax, %cr4
/* Setup early boot stage 4 level pagetables. */
- movq $(boot_level4_pgt - __START_KERNEL_map), %rax
+ movq $(init_level4_pgt - __START_KERNEL_map), %rax
movq %rax, %cr3
/* Check if nx is implemented */
@@ -266,9 +266,19 @@ ENTRY(name)
i = i + 1 ; \
.endr
+ /*
+ * This default setting generates an ident mapping at address 0x100000
+ * and a mapping for the kernel that precisely maps virtual address
+ * 0xffffffff80000000 to physical address 0x000000. (always using
+ * 2Mbyte large pages provided by PAE mode)
+ */
NEXT_PAGE(init_level4_pgt)
- /* This gets initialized in x86_64_start_kernel */
- .fill 512,8,0
+ .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
+ .fill 257,8,0
+ .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
+ .fill 252,8,0
+ /* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
+ .quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE
NEXT_PAGE(level3_ident_pgt)
.quad level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
@@ -299,27 +309,6 @@ NEXT_PAGE(level2_kernel_pgt)
#undef NEXT_PAGE
.data
-
-#ifndef CONFIG_HOTPLUG_CPU
- __INITDATA
-#endif
- /*
- * This default setting generates an ident mapping at address 0x100000
- * and a mapping for the kernel that precisely maps virtual address
- * 0xffffffff80000000 to physical address 0x000000. (always using
- * 2Mbyte large pages provided by PAE mode)
- */
- .align PAGE_SIZE
-ENTRY(boot_level4_pgt)
- .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
- .fill 257,8,0
- .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
- .fill 252,8,0
- /* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
- .quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE
-
- .data
-
.align 16
.globl cpu_gdt_descr
cpu_gdt_descr:
diff -puN arch/x86_64/kernel/setup64.c~x86_64-Remove-the-identity-mapping-as-early-as-possible arch/x86_64/kernel/setup64.c
--- linux-2.6.19-rc5-reloc/arch/x86_64/kernel/setup64.c~x86_64-Remove-the-identity-mapping-as-early-as-possible 2006-11-09 23:04:38.000000000 -0500
+++ linux-2.6.19-rc5-reloc-root/arch/x86_64/kernel/setup64.c 2006-11-09 23:04:38.000000000 -0500
@@ -202,7 +202,6 @@ void __cpuinit cpu_init (void)
/* CPU 0 is initialised in head64.c */
if (cpu != 0) {
pda_init(cpu);
- zap_low_mappings(cpu);
} else
estacks = boot_exception_stacks;
diff -puN arch/x86_64/kernel/setup.c~x86_64-Remove-the-identity-mapping-as-early-as-possible arch/x86_64/kernel/setup.c
--- linux-2.6.19-rc5-reloc/arch/x86_64/kernel/setup.c~x86_64-Remove-the-identity-mapping-as-early-as-possible 2006-11-09 23:04:38.000000000 -0500
+++ linux-2.6.19-rc5-reloc-root/arch/x86_64/kernel/setup.c 2006-11-09 23:04:38.000000000 -0500
@@ -396,8 +396,6 @@ void __init setup_arch(char **cmdline_p)
dmi_scan_machine();
- zap_low_mappings(0);
-
#ifdef CONFIG_ACPI
/*
* Initialize the ACPI boot-time table parser (gets the RSDP and SDT).
diff -puN arch/x86_64/mm/init.c~x86_64-Remove-the-identity-mapping-as-early-as-possible arch/x86_64/mm/init.c
--- linux-2.6.19-rc5-reloc/arch/x86_64/mm/init.c~x86_64-Remove-the-identity-mapping-as-early-as-possible 2006-11-09 23:04:38.000000000 -0500
+++ linux-2.6.19-rc5-reloc-root/arch/x86_64/mm/init.c 2006-11-09 23:04:38.000000000 -0500
@@ -378,21 +378,6 @@ void __meminit init_memory_mapping(unsig
__flush_tlb_all();
}
-void __cpuinit zap_low_mappings(int cpu)
-{
- if (cpu == 0) {
- pgd_t *pgd = pgd_offset_k(0UL);
- pgd_clear(pgd);
- } else {
- /*
- * For AP's, zap the low identity mappings by changing the cr3
- * to init_level4_pgt and doing local flush tlb all
- */
- asm volatile("movq %0,%%cr3" :: "r" (__pa_symbol(&init_level4_pgt)));
- }
- __flush_tlb_all();
-}
-
#ifndef CONFIG_NUMA
void __init paging_init(void)
{
@@ -576,15 +561,6 @@ void __init mem_init(void)
reservedpages << (PAGE_SHIFT-10),
datasize >> 10,
initsize >> 10);
-
-#ifdef CONFIG_SMP
- /*
- * Sync boot_level4_pgt mappings with the init_level4_pgt
- * except for the low identity mappings which are already zapped
- * in init_level4_pgt. This sync-up is essential for AP's bringup
- */
- memcpy(boot_level4_pgt+1, init_level4_pgt+1, (PTRS_PER_PGD-1)*sizeof(pgd_t));
-#endif
}
void free_init_pages(char *what, unsigned long begin, unsigned long end)
diff -puN include/asm-x86_64/pgtable.h~x86_64-Remove-the-identity-mapping-as-early-as-possible include/asm-x86_64/pgtable.h
--- linux-2.6.19-rc5-reloc/include/asm-x86_64/pgtable.h~x86_64-Remove-the-identity-mapping-as-early-as-possible 2006-11-09 23:04:38.000000000 -0500
+++ linux-2.6.19-rc5-reloc-root/include/asm-x86_64/pgtable.h 2006-11-09 23:04:38.000000000 -0500
@@ -18,7 +18,6 @@ extern pud_t level3_kernel_pgt[512];
extern pud_t level3_ident_pgt[512];
extern pmd_t level2_kernel_pgt[512];
extern pgd_t init_level4_pgt[];
-extern pgd_t boot_level4_pgt[];
extern unsigned long __supported_pte_mask;
#define swapper_pg_dir init_level4_pgt
diff -puN include/asm-x86_64/proto.h~x86_64-Remove-the-identity-mapping-as-early-as-possible include/asm-x86_64/proto.h
--- linux-2.6.19-rc5-reloc/include/asm-x86_64/proto.h~x86_64-Remove-the-identity-mapping-as-early-as-possible 2006-11-09 23:04:38.000000000 -0500
+++ linux-2.6.19-rc5-reloc-root/include/asm-x86_64/proto.h 2006-11-09 23:04:38.000000000 -0500
@@ -11,8 +11,6 @@ struct pt_regs;
extern void start_kernel(void);
extern void pda_init(int);
-extern void zap_low_mappings(int cpu);
-
extern void early_idt_handler(void);
extern void mcheck_init(struct cpuinfo_x86 *c);
_
-
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