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x86: Drop unnecessary kernel_eflags variable on 64-bit

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On 64 bit x86 we save the current eflags in cpu_init for use in
ret_from_fork. Strictly speaking reserved bits in EFLAGS should
be read as written but in practise it is unlikely that EFLAGS
could ever be extended in this way and the kernel alread clears
any undefined flags early on.

The equivalent 32 bit code simply hard codes 0x0202 as the new
EFLAGS.

This change makes 64 bit use the same mechanism to setup the
initial EFLAGS on fork. Note that 64 bit resets EFLAGS before
calling schedule_tail() as opposed to 32 bit which calls
schedule_tail() first. Therefore the correct value for EFLAGS
has opposite IF bit.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Andi Kleen <ak@linux.intel.com>
Acked-by: "H. Peter Anvin" <hpa@zytor.com>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Link: http://lkml.kernel.org/r/20120824195847.GA31628@moon
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Ian Campbell 2012-08-24 23:58:47 +04:00 committed by Ingo Molnar
parent 816afe4ff9
commit 6eebdda35e
3 changed files with 1 additions and 6 deletions
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1
arch/x86/include/asm/processor.h
View File

@ -423,7 +423,6 @@ DECLARE_INIT_PER_CPU(irq_stack_union);
DECLARE_PER_CPU(char *, irq_stack_ptr);
DECLARE_PER_CPU(unsigned int, irq_count);
extern unsigned long kernel_eflags;
extern asmlinkage void ignore_sysret(void);
#else /* X86_64 */
#ifdef CONFIG_CC_STACKPROTECTOR

4
arch/x86/kernel/cpu/common.c
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@ -1116,8 +1116,6 @@ void syscall_init(void)
X86_EFLAGS_TF|X86_EFLAGS_DF|X86_EFLAGS_IF|X86_EFLAGS_IOPL);
}
unsigned long kernel_eflags;
/*
* Copies of the original ist values from the tss are only accessed during
* debugging, no special alignment required.
@ -1299,8 +1297,6 @@ void __cpuinit cpu_init(void)
fpu_init();
xsave_init();
raw_local_save_flags(kernel_eflags);
if (is_uv_system())
uv_cpu_init();
}

2
arch/x86/kernel/entry_64.S
View File

@ -440,7 +440,7 @@ ENTRY(ret_from_fork)
LOCK ; btr $TIF_FORK,TI_flags(%r8)
pushq_cfi kernel_eflags(%rip)
pushq_cfi $0x0002
popfq_cfi # reset kernel eflags
call schedule_tail # rdi: 'prev' task parameter