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| author | H. Peter Anvin <hpa@zytor.com> | 2012-06-21 10:25:03 -0700 |
|---|---|---|
| committer | H. Peter Anvin <hpa@zytor.com> | 2012-06-21 10:25:03 -0700 |
| commit | 9751d7627582fc1cc64625d63bde9528c14f1544 (patch) | |
| tree | 33b0b58eb47f4bda4478c2d658019a1d2986cad8 /arch/x86/realmode | |
| parent | 2b1b712f050eaf0ac576591281446dc960c0afc5 (diff) | |
| download | lwn-9751d7627582fc1cc64625d63bde9528c14f1544.tar.gz lwn-9751d7627582fc1cc64625d63bde9528c14f1544.zip | |
x86-64, reboot: Be more paranoid in 64-bit reboot=bios
Be a bit more paranoid in the transition back to 16-bit mode. In
particular, in case the kernel is residing above the 4 GiB mark,
switch to the trampoline GDT, and make the jump after turning off
paging a far jump. In theory, none of this should matter, but it is
exactly the kind of things that broken SMM or virtualization software
could trip up on.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Link: http://lkml.kernel.org/r/tip-jopx7y6g6dbcx4tpal8q0jlr@git.kernel.org
Diffstat (limited to 'arch/x86/realmode')
| -rw-r--r-- | arch/x86/realmode/rm/reboot.S | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/arch/x86/realmode/rm/reboot.S b/arch/x86/realmode/rm/reboot.S index 6bf8feac5557..f932ea61d1c8 100644 --- a/arch/x86/realmode/rm/reboot.S +++ b/arch/x86/realmode/rm/reboot.S @@ -22,14 +22,18 @@ ENTRY(machine_real_restart_asm) #ifdef CONFIG_X86_64 + /* Switch to trampoline GDT as it is guaranteed < 4 GiB */ + movl $__KERNEL_DS, %eax + movl %eax, %ds + lgdtl pa_tr_gdt /* Disable paging to drop us out of long mode */ movl %cr0, %eax andl $~X86_CR0_PG, %eax movl %eax, %cr0 - jmp 1f /* "A branch" may be needed here, assume near is OK */ + ljmpl $__KERNEL32_CS, $pa_machine_real_restart_paging_off -1: +GLOBAL(machine_real_restart_paging_off) xorl %eax, %eax xorl %edx, %edx movl $MSR_EFER, %ecx |