* [PATCH 0/3] x86: slightly unify ret_from_fork
@ 2010-02-09 15:56 Ian Campbell
2010-02-09 15:56 ` [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit Ian Campbell
` (2 more replies)
0 siblings, 3 replies; 7+ messages in thread
From: Ian Campbell @ 2010-02-09 15:56 UTC (permalink / raw)
To: linux-kernel; +Cc: Ian Campbell, x86
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
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit.
2010-02-09 15:56 [PATCH 0/3] x86: slightly unify ret_from_fork Ian Campbell
@ 2010-02-09 15:56 ` Ian Campbell
2010-02-09 15:56 ` [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit Ian Campbell
2010-02-09 15:56 ` [PATCH 3/3] x86: ret_from_fork: use symbolic contants for bits in EFLAGS Ian Campbell
2 siblings, 0 replies; 7+ messages in thread
From: Ian Campbell @ 2010-02-09 15:56 UTC (permalink / raw)
To: linux-kernel; +Cc: Ian Campbell, x86
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
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit
2010-02-09 15:56 [PATCH 0/3] x86: slightly unify ret_from_fork Ian Campbell
2010-02-09 15:56 ` [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit Ian Campbell
@ 2010-02-09 15:56 ` Ian Campbell
2010-02-09 15:56 ` [PATCH 3/3] x86: ret_from_fork: use symbolic contants for bits in EFLAGS Ian Campbell
2 siblings, 0 replies; 7+ messages in thread
From: Ian Campbell @ 2010-02-09 15:56 UTC (permalink / raw)
To: linux-kernel; +Cc: Ian Campbell, x86
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
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH 3/3] x86: ret_from_fork: use symbolic contants for bits in EFLAGS
2010-02-09 15:56 [PATCH 0/3] x86: slightly unify ret_from_fork Ian Campbell
2010-02-09 15:56 ` [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit Ian Campbell
2010-02-09 15:56 ` [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit Ian Campbell
@ 2010-02-09 15:56 ` Ian Campbell
2 siblings, 0 replies; 7+ messages in thread
From: Ian Campbell @ 2010-02-09 15:56 UTC (permalink / raw)
To: linux-kernel; +Cc: Ian Campbell, x86
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
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [Q x86-64] on kernel_eflags
@ 2011-07-05 11:15 Cyrill Gorcunov
2011-07-05 13:00 ` [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit Ian Campbell
0 siblings, 1 reply; 7+ messages in thread
From: Cyrill Gorcunov @ 2011-07-05 11:15 UTC (permalink / raw)
To: Ian Campbell
Cc: LKML, Ingo Molnar, Thomas Gleixner, H. Peter Anvin, Brian Gerst,
Jan Beulich, Peter Zijlstra, Frederic Weisbecker
On Tue, Jul 05, 2011 at 12:00:56PM +0100, Ian Campbell wrote:
...
>
> I posted http://lkml.org/lkml/2010/2/9/155 to switch to the hardcoded
> version for 64 bit too. Is it worth my rebasing and reposting that?
I think so.
Cyrill
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit
2011-07-05 11:15 [Q x86-64] on kernel_eflags Cyrill Gorcunov
@ 2011-07-05 13:00 ` Ian Campbell
2011-07-06 9:41 ` Pekka Enberg
0 siblings, 1 reply; 7+ messages in thread
From: Ian Campbell @ 2011-07-05 13:00 UTC (permalink / raw)
To: Cyrill Gorcunov
Cc: linux-kernel, Ingo Molnar, Thomas Gleixner, H. Peter Anvin,
Brian Gerst, Jan Beulich, Peter Zijlstra, Frederic Weisbecker,
Ian Campbell, x86
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 | 7 ++++---
1 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index b50d142..9c28bd5 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -394,13 +394,14 @@ END(save_paranoid)
ENTRY(ret_from_fork)
DEFAULT_FRAME
- LOCK ; btr $TIF_FORK,TI_flags(%r8)
- pushq_cfi $0x0002
- popfq_cfi # reset kernel eflags
+ LOCK ; btr $TIF_FORK,TI_flags(%r8)
call schedule_tail # rdi: 'prev' task parameter
+ pushq_cfi $0x0202
+ popfq_cfi # reset kernel eflags
+
GET_THREAD_INFO(%rcx)
RESTORE_REST
--
1.7.2.5
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit
2011-07-05 13:00 ` [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit Ian Campbell
@ 2011-07-06 9:41 ` Pekka Enberg
0 siblings, 0 replies; 7+ messages in thread
From: Pekka Enberg @ 2011-07-06 9:41 UTC (permalink / raw)
To: Ian Campbell
Cc: Cyrill Gorcunov, linux-kernel, Ingo Molnar, Thomas Gleixner,
H. Peter Anvin, Brian Gerst, Jan Beulich, Peter Zijlstra,
Frederic Weisbecker, x86
On Tue, Jul 5, 2011 at 4:00 PM, Ian Campbell <ian.campbell@citrix.com> wrote:
> 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
Reviewed-by: Pekka Enberg <penberg@kernel.org>
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH 0/3] minor cleanups to EFLAGS initialisation in ret_from_fork
@ 2011-07-25 9:58 Ian Campbell
2011-07-25 10:03 ` [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit Ian Campbell
0 siblings, 1 reply; 7+ messages in thread
From: Ian Campbell @ 2011-07-25 9:58 UTC (permalink / raw)
To: linux-kernel; +Cc: Pekka Enberg, Cyrill Gorcunov, H. Peter Anvin, Andi Kleen
The following series removes the use of a global kernel_eflags variable
from the x86_64 ret_from_fork path and (very slightly) merges the 32 and
64 bit version of that code path.
kernel_eflags could be made a __read_mostly but actually there is no
reason to prefer the value at cpu_init() time to a compile time constant
value for the initial eflags after a fork.
Ian.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit
2011-07-25 9:58 [PATCH 0/3] minor cleanups to EFLAGS initialisation in ret_from_fork Ian Campbell
@ 2011-07-25 10:03 ` Ian Campbell
0 siblings, 0 replies; 7+ messages in thread
From: Ian Campbell @ 2011-07-25 10:03 UTC (permalink / raw)
To: linux-kernel
Cc: Pekka Enberg, Cyrill Gorcunov, H. Peter Anvin, Andi Kleen,
Ian Campbell, x86
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>
Reviewed-by: Pekka Enberg <penberg@kernel.org>
Acked-by: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: x86@kernel.org
---
arch/x86/kernel/entry_64.S | 7 ++++---
1 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index b50d142..9c28bd5 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -394,13 +394,14 @@ END(save_paranoid)
ENTRY(ret_from_fork)
DEFAULT_FRAME
- LOCK ; btr $TIF_FORK,TI_flags(%r8)
- pushq_cfi $0x0002
- popfq_cfi # reset kernel eflags
+ LOCK ; btr $TIF_FORK,TI_flags(%r8)
call schedule_tail # rdi: 'prev' task parameter
+ pushq_cfi $0x0202
+ popfq_cfi # reset kernel eflags
+
GET_THREAD_INFO(%rcx)
RESTORE_REST
--
1.7.2.5
^ permalink raw reply related [flat|nested] 7+ messages in thread
end of thread, other threads:[~2011-07-25 10:03 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
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2010-02-09 15:56 [PATCH 0/3] x86: slightly unify ret_from_fork Ian Campbell
2010-02-09 15:56 ` [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit Ian Campbell
2010-02-09 15:56 ` [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit Ian Campbell
2010-02-09 15:56 ` [PATCH 3/3] x86: ret_from_fork: use symbolic contants for bits in EFLAGS Ian Campbell
2011-07-05 11:15 [Q x86-64] on kernel_eflags Cyrill Gorcunov
2011-07-05 13:00 ` [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit Ian Campbell
2011-07-06 9:41 ` Pekka Enberg
2011-07-25 9:58 [PATCH 0/3] minor cleanups to EFLAGS initialisation in ret_from_fork Ian Campbell
2011-07-25 10:03 ` [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit Ian Campbell
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