[PATCH 0/3] Misc x86 cleanups

[PATCH 0/3] Misc x86 cleanups

[Brian Gerst]

Here are a few cleanups from the recent x86 entry code rewrite.

[PATCH 1/3] x86: Don't save/restore EFLAGS on task switch
[PATCH 2/3] x86-32: Remove GET_THREAD_INFO from entry code
[PATCH 3/3] x86-32: Remove asmlinkage_protect

 arch/x86/entry/entry_32.S        |  7 -------
 arch/x86/entry/entry_64.S        |  3 ---
 arch/x86/include/asm/linkage.h   | 34 ----------------------------------
 arch/x86/include/asm/switch_to.h |  4 +---
 4 files changed, 1 insertion(+), 47 deletions(-)

[PATCH 1/3] x86: Don't save/restore EFLAGS on task switch

[Brian Gerst]

Now that NT is filtered by the SYSENTER entry code, it is safe to skip saving and
restoring flags on task switch.  Also remove a leftover reset of flags on 64-bit
fork.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
---
 arch/x86/entry/entry_32.S        | 4 ----
 arch/x86/entry/entry_64.S        | 3 ---
 arch/x86/include/asm/switch_to.h | 4 +---
 3 files changed, 1 insertion(+), 10 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 10868aa..c84d99b 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -209,8 +209,6 @@ ENTRY(ret_from_fork)
 	call	schedule_tail
 	GET_THREAD_INFO(%ebp)
 	popl	%eax
-	pushl	$0x0202				# Reset kernel eflags
-	popfl
 
 	/* When we fork, we trace the syscall return in the child, too. */
 	movl    %esp, %eax
@@ -223,8 +221,6 @@ ENTRY(ret_from_kernel_thread)
 	call	schedule_tail
 	GET_THREAD_INFO(%ebp)
 	popl	%eax
-	pushl	$0x0202				# Reset kernel eflags
-	popfl
 	movl	PT_EBP(%esp), %eax
 	call	*PT_EBX(%esp)
 	movl	$0, PT_EAX(%esp)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 6344629..9ee0da1 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -372,9 +372,6 @@ END(ptregs_\func)
 ENTRY(ret_from_fork)
 	LOCK ; btr $TIF_FORK, TI_flags(%r8)
 
-	pushq	$0x0002
-	popfq					/* reset kernel eflags */
-
 	call	schedule_tail			/* rdi: 'prev' task parameter */
 
 	testb	$3, CS(%rsp)			/* from kernel_thread? */
diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index 751bf4b..8f321a1 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -39,8 +39,7 @@ do {									\
 	 */								\
 	unsigned long ebx, ecx, edx, esi, edi;				\
 									\
-	asm volatile("pushfl\n\t"		/* save    flags */	\
-		     "pushl %%ebp\n\t"		/* save    EBP   */	\
+	asm volatile("pushl %%ebp\n\t"		/* save    EBP   */	\
 		     "movl %%esp,%[prev_sp]\n\t"	/* save    ESP   */ \
 		     "movl %[next_sp],%%esp\n\t"	/* restore ESP   */ \
 		     "movl $1f,%[prev_ip]\n\t"	/* save    EIP   */	\
@@ -49,7 +48,6 @@ do {									\
 		     "jmp __switch_to\n"	/* regparm call  */	\
 		     "1:\t"						\
 		     "popl %%ebp\n\t"		/* restore EBP   */	\
-		     "popfl\n"			/* restore flags */	\
 									\
 		     /* output parameters */				\
 		     : [prev_sp] "=m" (prev->thread.sp),		\
-- 
2.5.5

Re: [PATCH 1/3] x86: Don't save/restore EFLAGS on task switch

[Andy Lutomirski]

On Wed, May 4, 2016 at 7:44 PM, Brian Gerst <brgerst@gmail.com> wrote:
> Now that NT is filtered by the SYSENTER entry code, it is safe to skip saving and
> restoring flags on task switch.  Also remove a leftover reset of flags on 64-bit
> fork.

Acked-by: Andy Lutomirski <luto@kernel.org>

[tip:x86/asm] x86/entry, sched/x86: Don't save/restore EFLAGS on task switch

[tip-bot for Brian Gerst]

Commit-ID:  092c74e420952c7cb68141731f2b562245b51eeb
Gitweb:     http://git.kernel.org/tip/092c74e420952c7cb68141731f2b562245b51eeb
Author:     Brian Gerst <brgerst@gmail.com>
AuthorDate: Wed, 4 May 2016 22:44:36 -0400
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 5 May 2016 08:37:30 +0200

x86/entry, sched/x86: Don't save/restore EFLAGS on task switch

Now that NT is filtered by the SYSENTER entry code, it is safe to skip saving and
restoring flags on task switch.  Also remove a leftover reset of flags on 64-bit
fork.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1462416278-11974-2-git-send-email-brgerst@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/entry/entry_32.S        | 4 ----
 arch/x86/entry/entry_64.S        | 3 ---
 arch/x86/include/asm/switch_to.h | 4 +---
 3 files changed, 1 insertion(+), 10 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 10868aa..c84d99b 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -209,8 +209,6 @@ ENTRY(ret_from_fork)
 	call	schedule_tail
 	GET_THREAD_INFO(%ebp)
 	popl	%eax
-	pushl	$0x0202				# Reset kernel eflags
-	popfl
 
 	/* When we fork, we trace the syscall return in the child, too. */
 	movl    %esp, %eax
@@ -223,8 +221,6 @@ ENTRY(ret_from_kernel_thread)
 	call	schedule_tail
 	GET_THREAD_INFO(%ebp)
 	popl	%eax
-	pushl	$0x0202				# Reset kernel eflags
-	popfl
 	movl	PT_EBP(%esp), %eax
 	call	*PT_EBX(%esp)
 	movl	$0, PT_EAX(%esp)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 6344629..9ee0da1 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -372,9 +372,6 @@ END(ptregs_\func)
 ENTRY(ret_from_fork)
 	LOCK ; btr $TIF_FORK, TI_flags(%r8)
 
-	pushq	$0x0002
-	popfq					/* reset kernel eflags */
-
 	call	schedule_tail			/* rdi: 'prev' task parameter */
 
 	testb	$3, CS(%rsp)			/* from kernel_thread? */
diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index 751bf4b..8f321a1 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -39,8 +39,7 @@ do {									\
 	 */								\
 	unsigned long ebx, ecx, edx, esi, edi;				\
 									\
-	asm volatile("pushfl\n\t"		/* save    flags */	\
-		     "pushl %%ebp\n\t"		/* save    EBP   */	\
+	asm volatile("pushl %%ebp\n\t"		/* save    EBP   */	\
 		     "movl %%esp,%[prev_sp]\n\t"	/* save    ESP   */ \
 		     "movl %[next_sp],%%esp\n\t"	/* restore ESP   */ \
 		     "movl $1f,%[prev_ip]\n\t"	/* save    EIP   */	\
@@ -49,7 +48,6 @@ do {									\
 		     "jmp __switch_to\n"	/* regparm call  */	\
 		     "1:\t"						\
 		     "popl %%ebp\n\t"		/* restore EBP   */	\
-		     "popfl\n"			/* restore flags */	\
 									\
 		     /* output parameters */				\
 		     : [prev_sp] "=m" (prev->thread.sp),		\

[PATCH 2/3] x86-32: Remove GET_THREAD_INFO from entry code

[Brian Gerst]

The entry code used to cache the thread_info pointer in the EBP register, but
all the code that used it has been moved to C.  Remove the unused code to
get the pointer.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
---
 arch/x86/entry/entry_32.S | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index c84d99b..983e5d3 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -207,7 +207,6 @@
 ENTRY(ret_from_fork)
 	pushl	%eax
 	call	schedule_tail
-	GET_THREAD_INFO(%ebp)
 	popl	%eax
 
 	/* When we fork, we trace the syscall return in the child, too. */
@@ -219,7 +218,6 @@ END(ret_from_fork)
 ENTRY(ret_from_kernel_thread)
 	pushl	%eax
 	call	schedule_tail
-	GET_THREAD_INFO(%ebp)
 	popl	%eax
 	movl	PT_EBP(%esp), %eax
 	call	*PT_EBX(%esp)
@@ -247,7 +245,6 @@ ENDPROC(ret_from_kernel_thread)
 ret_from_exception:
 	preempt_stop(CLBR_ANY)
 ret_from_intr:
-	GET_THREAD_INFO(%ebp)
 #ifdef CONFIG_VM86
 	movl	PT_EFLAGS(%esp), %eax		# mix EFLAGS and CS
 	movb	PT_CS(%esp), %al
-- 
2.5.5

Re: [PATCH 2/3] x86-32: Remove GET_THREAD_INFO from entry code

[Andy Lutomirski]

On Wed, May 4, 2016 at 7:44 PM, Brian Gerst <brgerst@gmail.com> wrote:
> The entry code used to cache the thread_info pointer in the EBP register, but
> all the code that used it has been moved to C.  Remove the unused code to
> get the pointer.

Acked-by: Andy Lutomirski <luto@kernel.org>

[tip:x86/asm] x86/entry/32: Remove GET_THREAD_INFO() from entry code

[tip-bot for Brian Gerst]

Commit-ID:  1e17880371f85d3d866962e04ba3567c0654a125
Gitweb:     http://git.kernel.org/tip/1e17880371f85d3d866962e04ba3567c0654a125
Author:     Brian Gerst <brgerst@gmail.com>
AuthorDate: Wed, 4 May 2016 22:44:37 -0400
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 5 May 2016 08:37:30 +0200

x86/entry/32: Remove GET_THREAD_INFO() from entry code

The entry code used to cache the thread_info pointer in the EBP register,
but all the code that used it has been moved to C.  Remove the unused
code to get the pointer.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1462416278-11974-3-git-send-email-brgerst@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/entry/entry_32.S | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index c84d99b..983e5d3 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -207,7 +207,6 @@
 ENTRY(ret_from_fork)
 	pushl	%eax
 	call	schedule_tail
-	GET_THREAD_INFO(%ebp)
 	popl	%eax
 
 	/* When we fork, we trace the syscall return in the child, too. */
@@ -219,7 +218,6 @@ END(ret_from_fork)
 ENTRY(ret_from_kernel_thread)
 	pushl	%eax
 	call	schedule_tail
-	GET_THREAD_INFO(%ebp)
 	popl	%eax
 	movl	PT_EBP(%esp), %eax
 	call	*PT_EBX(%esp)
@@ -247,7 +245,6 @@ ENDPROC(ret_from_kernel_thread)
 ret_from_exception:
 	preempt_stop(CLBR_ANY)
 ret_from_intr:
-	GET_THREAD_INFO(%ebp)
 #ifdef CONFIG_VM86
 	movl	PT_EFLAGS(%esp), %eax		# mix EFLAGS and CS
 	movb	PT_CS(%esp), %al

[PATCH 3/3] x86-32: Remove asmlinkage_protect

[Brian Gerst]

Now that syscalls are called from C code, which copies the args to new stack
slots instead of overlaying pt_regs, asmlinkage_protect is no longer needed.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
---
 arch/x86/include/asm/linkage.h | 34 ----------------------------------
 1 file changed, 34 deletions(-)

diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h
index 79327e9..0ccb26d 100644
--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@@ -8,40 +8,6 @@
 
 #ifdef CONFIG_X86_32
 #define asmlinkage CPP_ASMLINKAGE __attribute__((regparm(0)))
-
-/*
- * Make sure the compiler doesn't do anything stupid with the
- * arguments on the stack - they are owned by the *caller*, not
- * the callee. This just fools gcc into not spilling into them,
- * and keeps it from doing tailcall recursion and/or using the
- * stack slots for temporaries, since they are live and "used"
- * all the way to the end of the function.
- *
- * NOTE! On x86-64, all the arguments are in registers, so this
- * only matters on a 32-bit kernel.
- */
-#define asmlinkage_protect(n, ret, args...) \
-	__asmlinkage_protect##n(ret, ##args)
-#define __asmlinkage_protect_n(ret, args...) \
-	__asm__ __volatile__ ("" : "=r" (ret) : "0" (ret), ##args)
-#define __asmlinkage_protect0(ret) \
-	__asmlinkage_protect_n(ret)
-#define __asmlinkage_protect1(ret, arg1) \
-	__asmlinkage_protect_n(ret, "m" (arg1))
-#define __asmlinkage_protect2(ret, arg1, arg2) \
-	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2))
-#define __asmlinkage_protect3(ret, arg1, arg2, arg3) \
-	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3))
-#define __asmlinkage_protect4(ret, arg1, arg2, arg3, arg4) \
-	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
-			      "m" (arg4))
-#define __asmlinkage_protect5(ret, arg1, arg2, arg3, arg4, arg5) \
-	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
-			      "m" (arg4), "m" (arg5))
-#define __asmlinkage_protect6(ret, arg1, arg2, arg3, arg4, arg5, arg6) \
-	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
-			      "m" (arg4), "m" (arg5), "m" (arg6))
-
 #endif /* CONFIG_X86_32 */
 
 #ifdef __ASSEMBLY__
-- 
2.5.5

Re: [PATCH 3/3] x86-32: Remove asmlinkage_protect

[Andy Lutomirski]

On Wed, May 4, 2016 at 7:44 PM, Brian Gerst <brgerst@gmail.com> wrote:
> Now that syscalls are called from C code, which copies the args to new stack
> slots instead of overlaying pt_regs, asmlinkage_protect is no longer needed.

Acked-by: Andy Lutomirski <luto@kernel.org>

asmlinkage_protect was pretty gross...

--Andy

[tip:x86/asm] x86/entry/32: Remove asmlinkage_protect()

[tip-bot for Brian Gerst]

Commit-ID:  0676b4e0a1940a6b7ae3156bd212ca9032a29c30
Gitweb:     http://git.kernel.org/tip/0676b4e0a1940a6b7ae3156bd212ca9032a29c30
Author:     Brian Gerst <brgerst@gmail.com>
AuthorDate: Wed, 4 May 2016 22:44:38 -0400
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 5 May 2016 08:37:31 +0200

x86/entry/32: Remove asmlinkage_protect()

Now that syscalls are called from C code, which copies the args to
new stack slots instead of overlaying pt_regs, asmlinkage_protect()
is no longer needed.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1462416278-11974-4-git-send-email-brgerst@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/linkage.h | 34 ----------------------------------
 1 file changed, 34 deletions(-)

diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h
index 79327e9..0ccb26d 100644
--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@@ -8,40 +8,6 @@
 
 #ifdef CONFIG_X86_32
 #define asmlinkage CPP_ASMLINKAGE __attribute__((regparm(0)))
-
-/*
- * Make sure the compiler doesn't do anything stupid with the
- * arguments on the stack - they are owned by the *caller*, not
- * the callee. This just fools gcc into not spilling into them,
- * and keeps it from doing tailcall recursion and/or using the
- * stack slots for temporaries, since they are live and "used"
- * all the way to the end of the function.
- *
- * NOTE! On x86-64, all the arguments are in registers, so this
- * only matters on a 32-bit kernel.
- */
-#define asmlinkage_protect(n, ret, args...) \
-	__asmlinkage_protect##n(ret, ##args)
-#define __asmlinkage_protect_n(ret, args...) \
-	__asm__ __volatile__ ("" : "=r" (ret) : "0" (ret), ##args)
-#define __asmlinkage_protect0(ret) \
-	__asmlinkage_protect_n(ret)
-#define __asmlinkage_protect1(ret, arg1) \
-	__asmlinkage_protect_n(ret, "m" (arg1))
-#define __asmlinkage_protect2(ret, arg1, arg2) \
-	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2))
-#define __asmlinkage_protect3(ret, arg1, arg2, arg3) \
-	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3))
-#define __asmlinkage_protect4(ret, arg1, arg2, arg3, arg4) \
-	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
-			      "m" (arg4))
-#define __asmlinkage_protect5(ret, arg1, arg2, arg3, arg4, arg5) \
-	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
-			      "m" (arg4), "m" (arg5))
-#define __asmlinkage_protect6(ret, arg1, arg2, arg3, arg4, arg5, arg6) \
-	__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
-			      "m" (arg4), "m" (arg5), "m" (arg6))
-
 #endif /* CONFIG_X86_32 */
 
 #ifdef __ASSEMBLY__