linux-kernel - [PATCH 7/9] x86/asm/entry/32: tidy up some instructions

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Date:	Tue, 31 Mar 2015 19:00:09 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 7/9] x86/asm/entry/32: tidy up some instructions

After TESTs, use logically correct JZ mnemonic instead of JE
(this doesn't change code).

Tidy up CMPW insns:

Modern CPUs are not good with 16-bit operations.
The instructions with 16-bit immediates are especially bad,
on many CPUs they cause length changing prefix stall
in the decoders, costing ~6 cycles to recover.

Replace CMPWs with CMPLs.
Of these, for form with 8-bit sign-extended immediates
it is a win because they are smaller now
(no 0x66 prefix anymore);
ones with 16-bit immediates are faster.

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
CC: Linus Torvalds <torvalds@...ux-foundation.org>
CC: Steven Rostedt <rostedt@...dmis.org>
CC: Ingo Molnar <mingo@...nel.org>
CC: Borislav Petkov <bp@...en8.de>
CC: "H. Peter Anvin" <hpa@...or.com>
CC: Andy Lutomirski <luto@...capital.net>
CC: Oleg Nesterov <oleg@...hat.com>
CC: Frederic Weisbecker <fweisbec@...il.com>
CC: Alexei Starovoitov <ast@...mgrid.com>
CC: Will Drewry <wad@...omium.org>
CC: Kees Cook <keescook@...omium.org>
CC: x86@...nel.org
CC: linux-kernel@...r.kernel.org
---
 arch/x86/kernel/entry_32.S | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 4c8cc34..9a31d5e 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -432,7 +432,7 @@ sysenter_after_call:
 	TRACE_IRQS_OFF
 	movl TI_flags(%ebp), %ecx
 	testl $_TIF_ALLWORK_MASK, %ecx
-	jne sysexit_audit
+	jnz sysexit_audit
 sysenter_exit:
 /* if something modifies registers it must also disable sysexit */
 	movl PT_EIP(%esp), %edx
@@ -460,7 +460,7 @@ sysenter_audit:
 
 sysexit_audit:
 	testl $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT), %ecx
-	jne syscall_exit_work
+	jnz syscall_exit_work
 	TRACE_IRQS_ON
 	ENABLE_INTERRUPTS(CLBR_ANY)
 	movl %eax,%edx		/* second arg, syscall return value */
@@ -472,7 +472,7 @@ sysexit_audit:
 	TRACE_IRQS_OFF
 	movl TI_flags(%ebp), %ecx
 	testl $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT), %ecx
-	jne syscall_exit_work
+	jnz syscall_exit_work
 	movl PT_EAX(%esp),%eax	/* reload syscall return value */
 	jmp sysenter_exit
 #endif
@@ -510,7 +510,7 @@ syscall_exit:
 	TRACE_IRQS_OFF
 	movl TI_flags(%ebp), %ecx
 	testl $_TIF_ALLWORK_MASK, %ecx	# current->work
-	jne syscall_exit_work
+	jnz syscall_exit_work
 
 restore_all:
 	TRACE_IRQS_IRET
@@ -612,7 +612,7 @@ work_notifysig:				# deal with pending signals and
 #ifdef CONFIG_VM86
 	testl $X86_EFLAGS_VM, PT_EFLAGS(%esp)
 	movl %esp, %eax
-	jne work_notifysig_v86		# returning to kernel-space or
+	jnz work_notifysig_v86		# returning to kernel-space or
 					# vm86-space
 1:
 #else
@@ -708,7 +708,7 @@ END(sysenter_badsys)
 #ifdef CONFIG_X86_ESPFIX32
 	movl %ss, %eax
 	/* see if on espfix stack */
-	cmpw $__ESPFIX_SS, %ax
+	cmpl $__ESPFIX_SS, %eax
 	jne 27f
 	movl $__KERNEL_DS, %eax
 	movl %eax, %ds
@@ -1275,7 +1275,7 @@ END(page_fault)
  * the instruction that would have done it for sysenter.
  */
 .macro FIX_STACK offset ok label
-	cmpw $__KERNEL_CS, 4(%esp)
+	cmpl $__KERNEL_CS, 4(%esp)
 	jne \ok
 \label:
 	movl TSS_sysenter_sp0 + \offset(%esp), %esp
@@ -1318,7 +1318,7 @@ ENTRY(nmi)
 #ifdef CONFIG_X86_ESPFIX32
 	pushl_cfi %eax
 	movl %ss, %eax
-	cmpw $__ESPFIX_SS, %ax
+	cmpl $__ESPFIX_SS, %eax
 	popl_cfi %eax
 	je nmi_espfix_stack
 #endif
@@ -1352,7 +1352,7 @@ nmi_stack_fixup:
 
 nmi_debug_stack_check:
 	/* We have a RING0_INT_FRAME here */
-	cmpw $__KERNEL_CS,16(%esp)
+	cmpl $__KERNEL_CS,16(%esp)
 	jne nmi_stack_correct
 	cmpl $debug,(%esp)
 	jb nmi_stack_correct
-- 
1.8.1.4

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