linux-kernel - [PATCH 4.9 52/87] x86/process: Optimize TIF

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Message-Id: <20180521210425.024101773@linuxfoundation.org>
Date:   Mon, 21 May 2018 23:11:28 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        David Woodhouse <dwmw@...zon.co.uk>
Subject: [PATCH 4.9 52/87] x86/process: Optimize TIF_NOTSC switch

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Thomas Gleixner <tglx@...utronix.de>

commit 5a920155e388ec22a22e0532fb695b9215c9b34d upstream

Provide and use a toggle helper instead of doing it with a branch.

x86_64: arch/x86/kernel/process.o
text	   data	    bss	    dec	    hex
3008	   8577	     16	  11601	   2d51 Before
2976       8577      16	  11569	   2d31 After

i386: arch/x86/kernel/process.o
text	   data	    bss	    dec	    hex
2925	   8673	      8	  11606	   2d56 Before
2893	   8673       8	  11574	   2d36 After

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andy Lutomirski <luto@...nel.org>
Link: http://lkml.kernel.org/r/20170214081104.9244-4-khuey@kylehuey.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/include/asm/tlbflush.h |   10 ++++++++++
 arch/x86/kernel/process.c       |   22 ++++------------------
 2 files changed, 14 insertions(+), 18 deletions(-)

--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -111,6 +111,16 @@ static inline void cr4_clear_bits(unsign
 	}
 }
 
+static inline void cr4_toggle_bits(unsigned long mask)
+{
+	unsigned long cr4;
+
+	cr4 = this_cpu_read(cpu_tlbstate.cr4);
+	cr4 ^= mask;
+	this_cpu_write(cpu_tlbstate.cr4, cr4);
+	__write_cr4(cr4);
+}
+
 /* Read the CR4 shadow. */
 static inline unsigned long cr4_read_shadow(void)
 {
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -134,11 +134,6 @@ void flush_thread(void)
 	fpu__clear(&tsk->thread.fpu);
 }
 
-static void hard_disable_TSC(void)
-{
-	cr4_set_bits(X86_CR4_TSD);
-}
-
 void disable_TSC(void)
 {
 	preempt_disable();
@@ -147,15 +142,10 @@ void disable_TSC(void)
 		 * Must flip the CPU state synchronously with
 		 * TIF_NOTSC in the current running context.
 		 */
-		hard_disable_TSC();
+		cr4_set_bits(X86_CR4_TSD);
 	preempt_enable();
 }
 
-static void hard_enable_TSC(void)
-{
-	cr4_clear_bits(X86_CR4_TSD);
-}
-
 static void enable_TSC(void)
 {
 	preempt_disable();
@@ -164,7 +154,7 @@ static void enable_TSC(void)
 		 * Must flip the CPU state synchronously with
 		 * TIF_NOTSC in the current running context.
 		 */
-		hard_enable_TSC();
+		cr4_clear_bits(X86_CR4_TSD);
 	preempt_enable();
 }
 
@@ -238,12 +228,8 @@ void __switch_to_xtra(struct task_struct
 		wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
 	}
 
-	if ((tifp ^ tifn) & _TIF_NOTSC) {
-		if (tifn & _TIF_NOTSC)
-			hard_disable_TSC();
-		else
-			hard_enable_TSC();
-	}
+	if ((tifp ^ tifn) & _TIF_NOTSC)
+		cr4_toggle_bits(X86_CR4_TSD);
 }
 
 /*