[PATCH 0/3] x86: slightly unify ret_from_fork

[PATCH 0/3] x86: slightly unify ret_from_fork

[Ian Campbell]

I came across some minor differences between the 32 and 64 bit
implementations of ret_from_fork. Although I don't expect this is code
which can realistically be completely unified there seemed to be some
value in making the two look a bit more similar.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: x86@kernel.org

[PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit.

[Ian Campbell]

For no reason that I can determine 64 bit x86 saves the current eflags
in cpu_init purely for use in ret_from_fork. The equivalent 32 bit
code simply hard codes 0x0202 as the new EFLAGS which seems safer than
relying on a potentially arbitrary EFLAGS saved during cpu_init.

Original i386 changeset
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=47a5c6fa0e204a2b63309c648bb2fde36836c826
Original x86_64 changset
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=658fdbef66e5e9be79b457edc2cbbb3add840aa9

The only comment in the later indicates that it is following the
former, but not why it differs in this way.

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. This will be fixed in a subsequent patch.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: x86@kernel.org
---
 arch/x86/kernel/cpu/common.c |    4 ----
 arch/x86/kernel/entry_64.S   |    2 +-
 2 files changed, 1 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 4868e4a..ab766b2 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1040,8 +1040,6 @@ 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.
@@ -1189,8 +1187,6 @@ void __cpuinit cpu_init(void)
 
 	fpu_init();
 
-	raw_local_save_flags(kernel_eflags);
-
 	if (is_uv_system())
 		uv_cpu_init();
 }
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 0697ff1..18e4c59 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -398,7 +398,7 @@ ENTRY(ret_from_fork)
 
 	LOCK ; btr $TIF_FORK,TI_flags(%r8)
 
-	push kernel_eflags(%rip)
+	push $0x0002
 	CFI_ADJUST_CFA_OFFSET 8
 	popf					# reset kernel eflags
 	CFI_ADJUST_CFA_OFFSET -8
-- 
1.5.6.5

[PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit

[Ian Campbell]

The 64 bit version resets EFLAGS before calling schedule_tail() and
therefore leaves EFLAGS.IF clear. 32 bit resets EFLAGS after calling
schedule_tail() and therefore leaves EFLAGS.IF set. I don't think
there is any practical difference between the two approaches since
interrupts are actually reenabled within schedule_tail
(schedule_tail->finish_task_switch->finish_lock_switch->raw_spin_unlock_irq->...->local_irq_enable)
so arbitrarily pick the 32 bit version and make 64 bit look like that.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: x86@kernel.org
---
 arch/x86/kernel/entry_64.S |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 18e4c59..b771c2f 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -398,13 +398,13 @@ ENTRY(ret_from_fork)
 
 	LOCK ; btr $TIF_FORK,TI_flags(%r8)
 
-	push $0x0002
+	call schedule_tail			# rdi: 'prev' task parameter
+
+	push $0x0202
 	CFI_ADJUST_CFA_OFFSET 8
 	popf					# reset kernel eflags
 	CFI_ADJUST_CFA_OFFSET -8
 
-	call schedule_tail			# rdi: 'prev' task parameter
-
 	GET_THREAD_INFO(%rcx)
 
 	RESTORE_REST
-- 
1.5.6.5

[PATCH 3/3] x86: ret_from_fork: use symbolic contants for bits in EFLAGS

[Ian Campbell]

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: x86@kernel.org
---
 arch/x86/kernel/entry_32.S |    2 +-
 arch/x86/kernel/entry_64.S |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 44a8e0d..02a5a18 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -325,7 +325,7 @@ ENTRY(ret_from_fork)
 	GET_THREAD_INFO(%ebp)
 	popl %eax
 	CFI_ADJUST_CFA_OFFSET -4
-	pushl $0x0202			# Reset kernel eflags
+	pushl $(X86_EFLAGS_IF|0x2)	# Reset kernel eflags
 	CFI_ADJUST_CFA_OFFSET 4
 	popfl
 	CFI_ADJUST_CFA_OFFSET -4
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index b771c2f..f5ceffa 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -400,7 +400,7 @@ ENTRY(ret_from_fork)
 
 	call schedule_tail			# rdi: 'prev' task parameter
 
-	push $0x0202
+	push $(X86_EFLAGS_IF|0x2)
 	CFI_ADJUST_CFA_OFFSET 8
 	popf					# reset kernel eflags
 	CFI_ADJUST_CFA_OFFSET -8
-- 
1.5.6.5

[PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit.

[Ian Campbell]

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 (fixed to
use symbolic constants in a subsequent patch).

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. This will be fixed in a subsequent patch.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: x86@kernel.org
---
 arch/x86/include/asm/processor.h |    1 -
 arch/x86/kernel/cpu/common.c     |    4 ----
 arch/x86/kernel/entry_64.S       |    2 +-
 3 files changed, 1 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 2193715..698af88 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -398,7 +398,6 @@ 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
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 22a073d..178c3b4 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1077,8 +1077,6 @@ 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.
@@ -1231,8 +1229,6 @@ void __cpuinit cpu_init(void)
 	fpu_init();
 	xsave_init();
 
-	raw_local_save_flags(kernel_eflags);
-
 	if (is_uv_system())
 		uv_cpu_init();
 }
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index e13329d..b50d142 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -396,7 +396,7 @@ 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
-- 
1.7.2.5

Re: [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit.

[H. Peter Anvin]

On 07/06/2011 04:17 PM, Andi Kleen wrote:
>> Well lets ask Linus and Andi?
> 
> The original idea was that if someone extends EFLAGS with new bits
> the BIOS could set them.  Strictly said the Intel Manual 
> specifies that ("reserved bits -- always set to values previously read")
>  
> But that never really worked out and I don't think anyone
> would dare extending it now.  So hardcoding is fine I guess.
> 

We already clear any undefined flags almost as soon as we enter the
kernel... and quite rightly so, because there are BIOSes which leave
random crap in the flags.

It is very different from what an *application* should do in this case,
however.

	-hpa

Re: [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit.

[Andi Kleen]

> Well lets ask Linus and Andi?

The original idea was that if someone extends EFLAGS with new bits
the BIOS could set them.  Strictly said the Intel Manual 
specifies that ("reserved bits -- always set to values previously read")
 
But that never really worked out and I don't think anyone
would dare extending it now.  So hardcoding is fine I guess.

-Andi

Re: [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit.

[Cyrill Gorcunov]

On Wed, Jul 06, 2011 at 10:57:05AM +0100, Ian Campbell wrote:
> On Wed, 2011-07-06 at 10:46 +0100, Cyrill Gorcunov wrote:
> > On Wed, Jul 06, 2011 at 10:25:29AM +0100, Ian Campbell wrote:
> > ...
> > > > 
> > > > The whole series looks good to me, thanks Ian! I hope I don't
> > > > miss anything, so lets wait for more feedback ;)
> > > 
> > > Thanks. Actually I missed the extern declaration in asm/processor.h so
> > > this updated patch should be used instead:
> > > 
> > 
> > Great, thanks Ian. Have you a chance to run this series? ;)
> 
> Yeah I booted it before I posted it. I figured that the initscripts etc
> would be a sufficient test of fork() and that if it were wrong it would
> fall over pretty quickly and obviously.
> 
> Ian.
> 

OK, thanks!

	Cyrill

Re: [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit.

[Ian Campbell]

On Wed, 2011-07-06 at 10:46 +0100, Cyrill Gorcunov wrote:
> On Wed, Jul 06, 2011 at 10:25:29AM +0100, Ian Campbell wrote:
> ...
> > > 
> > > The whole series looks good to me, thanks Ian! I hope I don't
> > > miss anything, so lets wait for more feedback ;)
> > 
> > Thanks. Actually I missed the extern declaration in asm/processor.h so
> > this updated patch should be used instead:
> > 
> 
> Great, thanks Ian. Have you a chance to run this series? ;)

Yeah I booted it before I posted it. I figured that the initscripts etc
would be a sufficient test of fork() and that if it were wrong it would
fall over pretty quickly and obviously.

Ian.

Re: [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit.

[Cyrill Gorcunov]

On Wed, Jul 06, 2011 at 10:25:29AM +0100, Ian Campbell wrote:
...
> > 
> > The whole series looks good to me, thanks Ian! I hope I don't
> > miss anything, so lets wait for more feedback ;)
> 
> Thanks. Actually I missed the extern declaration in asm/processor.h so
> this updated patch should be used instead:
> 

Great, thanks Ian. Have you a chance to run this series? ;)

	Cyrill

Re: [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit.

[Pekka Enberg]

On Tue, Jul 5, 2011 at 4:00 PM, Ian Campbell <ian.campbell@citrix.com> wrote:
> For no reason that I can determine 64 bit x86 saves the current eflags
> in cpu_init purely for use in ret_from_fork. The equivalent 32 bit
> code simply hard codes 0x0202 as the new EFLAGS which seems safer than
> relying on a potentially arbitrary EFLAGS saved during cpu_init.
>
> Original i386 changeset
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=47a5c6fa0e204a2b63309c648bb2fde36836c826
> Original x86_64 changset
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=658fdbef66e5e9be79b457edc2cbbb3add840aa9
>
> The only comment in the later indicates that it is following the
> former, but not why it differs in this way.

Well lets ask Linus and Andi?

> 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. This will be fixed in a subsequent patch.
>
> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> Cc: x86@kernel.org
> ---
>  arch/x86/kernel/cpu/common.c |    4 ----
>  arch/x86/kernel/entry_64.S   |    2 +-
>  2 files changed, 1 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 22a073d..178c3b4 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1077,8 +1077,6 @@ 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.
> @@ -1231,8 +1229,6 @@ void __cpuinit cpu_init(void)
>        fpu_init();
>        xsave_init();
>
> -       raw_local_save_flags(kernel_eflags);
> -
>        if (is_uv_system())
>                uv_cpu_init();
>  }
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index e13329d..b50d142 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -396,7 +396,7 @@ 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

Re: [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit.

[Ian Campbell]

On Tue, 2011-07-05 at 17:28 +0400, Cyrill Gorcunov wrote:
> On Tue, Jul 05, 2011 at 02:00:12PM +0100, Ian Campbell wrote:
> > For no reason that I can determine 64 bit x86 saves the current eflags
> > in cpu_init purely for use in ret_from_fork. The equivalent 32 bit
> > code simply hard codes 0x0202 as the new EFLAGS which seems safer than
> > relying on a potentially arbitrary EFLAGS saved during cpu_init.
> > 
> > Original i386 changeset
> > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=47a5c6fa0e204a2b63309c648bb2fde36836c826
> > Original x86_64 changset
> > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=658fdbef66e5e9be79b457edc2cbbb3add840aa9
> > 
> > The only comment in the later indicates that it is following the
> > former, but not why it differs in this way.
> > 
> > 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. This will be fixed in a subsequent patch.
> > 
> > Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> > Cc: x86@kernel.org
> 
> The whole series looks good to me, thanks Ian! I hope I don't
> miss anything, so lets wait for more feedback ;)

Thanks. Actually I missed the extern declaration in asm/processor.h so
this updated patch should be used instead:

8<-----------------------------------------------

>From a450bf9e1c6e3f436c652b3e4d63b50c1f9848d4 Mon Sep 17 00:00:00 2001
From: Ian Campbell <ian.campbell@citrix.com>
Date: Wed, 6 Jul 2011 10:24:46 +0100
Subject: [PATCH] x86: drop unnecessary kernel_eflags variable from 64 bit.

For no reason that I can determine 64 bit x86 saves the current eflags
in cpu_init purely for use in ret_from_fork. The equivalent 32 bit
code simply hard codes 0x0202 as the new EFLAGS which seems safer than
relying on a potentially arbitrary EFLAGS saved during cpu_init.

Original i386 changeset
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=47a5c6fa0e204a2b63309c648bb2fde36836c826
Original x86_64 changset
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=658fdbef66e5e9be79b457edc2cbbb3add840aa9

The only comment in the later indicates that it is following the
former, but not why it differs in this way.

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. This will be fixed in a subsequent patch.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: x86@kernel.org
---
 arch/x86/include/asm/processor.h |    1 -
 arch/x86/kernel/cpu/common.c     |    4 ----
 arch/x86/kernel/entry_64.S       |    2 +-
 3 files changed, 1 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 2193715..698af88 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -398,7 +398,6 @@ 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
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 22a073d..178c3b4 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1077,8 +1077,6 @@ 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.
@@ -1231,8 +1229,6 @@ void __cpuinit cpu_init(void)
 	fpu_init();
 	xsave_init();
 
-	raw_local_save_flags(kernel_eflags);
-
 	if (is_uv_system())
 		uv_cpu_init();
 }
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index e13329d..b50d142 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -396,7 +396,7 @@ 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
-- 
1.7.2.5

Re: [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit.

[Cyrill Gorcunov]

On Tue, Jul 05, 2011 at 02:00:12PM +0100, Ian Campbell wrote:
> For no reason that I can determine 64 bit x86 saves the current eflags
> in cpu_init purely for use in ret_from_fork. The equivalent 32 bit
> code simply hard codes 0x0202 as the new EFLAGS which seems safer than
> relying on a potentially arbitrary EFLAGS saved during cpu_init.
> 
> Original i386 changeset
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=47a5c6fa0e204a2b63309c648bb2fde36836c826
> Original x86_64 changset
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=658fdbef66e5e9be79b457edc2cbbb3add840aa9
> 
> The only comment in the later indicates that it is following the
> former, but not why it differs in this way.
> 
> 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. This will be fixed in a subsequent patch.
> 
> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> Cc: x86@kernel.org

The whole series looks good to me, thanks Ian! I hope I don't
miss anything, so lets wait for more feedback ;)

	Cyrill

[PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit.

[Ian Campbell]

For no reason that I can determine 64 bit x86 saves the current eflags
in cpu_init purely for use in ret_from_fork. The equivalent 32 bit
code simply hard codes 0x0202 as the new EFLAGS which seems safer than
relying on a potentially arbitrary EFLAGS saved during cpu_init.

Original i386 changeset
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=47a5c6fa0e204a2b63309c648bb2fde36836c826
Original x86_64 changset
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=658fdbef66e5e9be79b457edc2cbbb3add840aa9

The only comment in the later indicates that it is following the
former, but not why it differs in this way.

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. This will be fixed in a subsequent patch.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: x86@kernel.org
---
 arch/x86/kernel/cpu/common.c |    4 ----
 arch/x86/kernel/entry_64.S   |    2 +-
 2 files changed, 1 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 22a073d..178c3b4 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1077,8 +1077,6 @@ 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.
@@ -1231,8 +1229,6 @@ void __cpuinit cpu_init(void)
 	fpu_init();
 	xsave_init();
 
-	raw_local_save_flags(kernel_eflags);
-
 	if (is_uv_system())
 		uv_cpu_init();
 }
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index e13329d..b50d142 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -396,7 +396,7 @@ 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
-- 
1.7.2.5