[PATCH] x86-64: Remove the identity mapping as early as possible

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@xmission.com>
Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andi Kleen <ak@suse.de>

diff --git a/arch/x86_64/kernel/head.S b/arch/x86_64/kernel/head.S
index 926aa2197aaaf46026ca1f470d85581eeff98199..c211e52f13332b71049a68aaf2b3ed730de7b04d 100644 (file)
--- a/arch/x86_64/kernel/head.S
+++ b/arch/x86_64/kernel/head.S
@@ -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 */
@@ -274,9 +274,19 @@ 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
@@ -307,27 +317,6 @@ 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 --git a/arch/x86_64/kernel/head64.c b/arch/x86_64/kernel/head64.c
index 5c529c1e3d6c9c3954691cccdb7ec7c72e5e8d32..6c34bdd22e2634df6bdb41cc1db8aba482ddf33f 100644 (file)
--- a/arch/x86_64/kernel/head64.c
+++ b/arch/x86_64/kernel/head64.c
@@ -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)
@@ -57,18 +65,15 @@ void __init x86_64_start_kernel(char * real_mode_data)
        /* clear bss before set_intr_gate with early_idt_handler */
        clear_bss();
 
+       /* Make NULL pointers segfault */
+       zap_identity_mappings();
+
        for (i = 0; i < IDT_ENTRIES; i++)
                set_intr_gate(i, early_idt_handler);
        asm volatile("lidt %0" :: "m" (idt_descr));
 
        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 --git a/arch/x86_64/kernel/setup.c b/arch/x86_64/kernel/setup.c
index 65e2bc551a2b3c8fdbe61f562cbc974849af9103..0e2b8df0ea64967e673a6cdc2cfb380e43b86abb 100644 (file)
--- a/arch/x86_64/kernel/setup.c
+++ b/arch/x86_64/kernel/setup.c
@@ -274,8 +274,6 @@ 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 --git a/arch/x86_64/kernel/setup64.c b/arch/x86_64/kernel/setup64.c
index 6a70b55f719d7cb47a463b3d8c638f7aae378c25..53064a9a365f1f92e707e6437d5edc0d0adbc516 100644 (file)
--- a/arch/x86_64/kernel/setup64.c
+++ b/arch/x86_64/kernel/setup64.c
@@ -201,7 +201,6 @@ 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 --git a/arch/x86_64/mm/init.c b/arch/x86_64/mm/init.c
index 4ab3d40aac9013f4587c3ac2766162425ca4569a..b0a607892183fceace0650639e2681b9537fe5d6 100644 (file)
--- a/arch/x86_64/mm/init.c
+++ b/arch/x86_64/mm/init.c
@@ -378,21 +378,6 @@ void __meminit init_memory_mapping(unsigned long start, unsigned long end)
        __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)
 {
@@ -569,15 +554,6 @@ 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 --git a/include/asm-x86_64/pgtable.h b/include/asm-x86_64/pgtable.h
index 5a5d43b3ef5d0d15d4c429f716aaaf6ff5b4616e..703f0243f27a884d97db491b355b817b4f237092 100644 (file)
--- a/include/asm-x86_64/pgtable.h
+++ b/include/asm-x86_64/pgtable.h
@@ -17,7 +17,6 @@ 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 --git a/include/asm-x86_64/proto.h b/include/asm-x86_64/proto.h
index 78427021d94a71cc6ac4c77651f9d99dce74b4d2..3f8f285138d272d8d100ce18f6f65bb4e6e60cb1 100644 (file)
--- a/include/asm-x86_64/proto.h
+++ b/include/asm-x86_64/proto.h
@@ -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);