linux-kernel - [tip:x86/asm] x86/asm/entry/64: Simplify optimistic SYSRET

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Message-ID: <tip-d441c1f2b73ec742c2e55be804ebc6fee130c77f@git.kernel.org>
Date:	Wed, 4 Mar 2015 14:56:46 -0800
From:	tip-bot for Denys Vlasenko <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	hpa@...or.com, fweisbec@...il.com, bp@...en8.de,
	luto@...capital.net, mingo@...nel.org, rostedt@...dmis.org,
	oleg@...hat.com, torvalds@...ux-foundation.org, ast@...mgrid.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	keescook@...omium.org, wad@...omium.org, dvlasenk@...hat.com
Subject: [tip:x86/asm] x86/asm/entry/64: Simplify optimistic SYSRET

Commit-ID:  d441c1f2b73ec742c2e55be804ebc6fee130c77f
Gitweb:     http://git.kernel.org/tip/d441c1f2b73ec742c2e55be804ebc6fee130c77f
Author:     Denys Vlasenko <dvlasenk@...hat.com>
AuthorDate: Thu, 26 Feb 2015 14:40:38 -0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 4 Mar 2015 22:50:52 +0100

x86/asm/entry/64: Simplify optimistic SYSRET

Avoid redundant load of %r11 (it is already loaded a few
instructions before).

Also simplify %rsp restoration, instead of two steps:

         add $0x80, %rsp
         mov 0x18(%rsp), %rsp

we can do a simplified single step to restore user-space RSP:

         mov 0x98(%rsp), %rsp

and get the same result.

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
Signed-off-by: Andy Lutomirski <luto@...capital.net>
[ Clarified the changelog. ]
Cc: Alexei Starovoitov <ast@...mgrid.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Will Drewry <wad@...omium.org>
Link: http://lkml.kernel.org/r/1aef69b346a6db0d99cdfb0f5ba83e8c985e27d7.1424989793.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/include/asm/calling.h | 3 +++
 arch/x86/kernel/entry_64.S     | 6 +++---
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/calling.h b/arch/x86/include/asm/calling.h
index 3374235..f1a962f 100644
--- a/arch/x86/include/asm/calling.h
+++ b/arch/x86/include/asm/calling.h
@@ -176,6 +176,9 @@ For 32-bit we have the following conventions - kernel is built with
 	.macro RESTORE_C_REGS_EXCEPT_RCX
 	RESTORE_C_REGS_HELPER 1,0,1,1,1
 	.endm
+	.macro RESTORE_C_REGS_EXCEPT_R11
+	RESTORE_C_REGS_HELPER 1,1,0,1,1
+	.endm
 	.macro RESTORE_RSI_RDI
 	RESTORE_C_REGS_HELPER 0,0,0,0,0
 	.endm
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 858e94e..bc15278 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -757,9 +757,9 @@ retint_swapgs:		/* return to user-space */
 	 */
 irq_return_via_sysret:
 	CFI_REMEMBER_STATE
-	RESTORE_C_REGS
-	REMOVE_PT_GPREGS_FROM_STACK 8
-	movq (RSP-RIP)(%rsp),%rsp
+	/* r11 is already restored (see code above) */
+	RESTORE_C_REGS_EXCEPT_R11
+	movq RSP(%rsp),%rsp
 	USERGS_SYSRET64
 	CFI_RESTORE_STATE
 
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