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Subject[PATCH] x86_64: disable identity mappings statically
Date
hi,

while browsing the page table setup code, I noticed the x86_64 head
code might not need the identity mappings at all.
It seems it's ok to switch it off completely from the begining,
unless I'm missing something.

wbr,
jirka


Signed-off-by: Jiri Olsa <jolsa@redhat.com>
---
arch/x86/kernel/head64.c | 10 ----------
arch/x86/kernel/head_64.S | 9 ++++-----
2 files changed, 4 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 2d2673c..620a9c3 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -27,13 +27,6 @@
#include <asm/trampoline.h>
#include <asm/bios_ebda.h>

-static void __init zap_identity_mappings(void)
-{
- pgd_t *pgd = pgd_offset_k(0UL);
- pgd_clear(pgd);
- __flush_tlb_all();
-}
-
/* Don't add a printk in there. printk relies on the PDA which is not initialized
yet. */
static void __init clear_bss(void)
@@ -74,9 +67,6 @@ 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();
-
/* Cleanup the over mapped high alias */
cleanup_highmap();

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 239046b..c55e6fa 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -341,13 +341,12 @@ ENTRY(name)

.data
/*
- * 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)
+ * This default setting generates 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)
- .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
.org init_level4_pgt + L4_PAGE_OFFSET*8, 0
.quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
.org init_level4_pgt + L4_START_KERNEL*8, 0
--
1.7.1

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