linux-kernel - [RFC PATCH v1.9 02/14] x86/asm/head: use a common function for starting CPUs

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Date:	Fri, 25 Mar 2016 14:34:49 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Jiri Kosina <jikos@...nel.org>, Jessica Yu <jeyu@...hat.com>,
	Miroslav Benes <mbenes@...e.cz>
Cc:	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
	Vojtech Pavlik <vojtech@...e.com>
Subject: [RFC PATCH v1.9 02/14] x86/asm/head: use a common function for starting CPUs

There are two different pieces of code for starting a CPU: start_cpu0()
and the end of secondary_startup_64().  They're identical except for the
stack setup.  Combine the common parts into a shared start_cpu()
function.

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/kernel/head_64.S | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 278270e..f2deae7 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -255,13 +255,15 @@ ENTRY(secondary_startup_64)
 	movl	$MSR_GS_BASE,%ecx
 	movl	initial_gs(%rip),%eax
 	movl	initial_gs+4(%rip),%edx
-	wrmsr	
+	wrmsr
 
 	/* rsi is pointer to real mode structure with interesting info.
 	   pass it to C */
 	movq	%rsi, %rdi
-	
-	/* Finally jump to run C code and to be on real kernel address
+
+ENTRY(start_cpu)
+	/*
+	 * Jump to run C code and to be on a real kernel address.
 	 * Since we are running on identity-mapped space we have to jump
 	 * to the full 64bit address, this is only possible as indirect
 	 * jump.  In addition we need to ensure %cs is set so we make this
@@ -290,6 +292,7 @@ ENTRY(secondary_startup_64)
 	pushq	$__KERNEL_CS	# set correct cs
 	pushq	%rax		# target address in negative space
 	lretq
+ENDPROC(start_cpu)
 
 #include "verify_cpu.S"
 
@@ -297,15 +300,11 @@ ENTRY(secondary_startup_64)
 /*
  * Boot CPU0 entry point. It's called from play_dead(). Everything has been set
  * up already except stack. We just set up stack here. Then call
- * start_secondary().
+ * start_secondary() via start_cpu().
  */
 ENTRY(start_cpu0)
-	movq initial_stack(%rip),%rsp
-	movq	initial_code(%rip),%rax
-	pushq	$0		# fake return address to stop unwinder
-	pushq	$__KERNEL_CS	# set correct cs
-	pushq	%rax		# target address in negative space
-	lretq
+	movq	initial_stack(%rip), %rsp
+	jmp	start_cpu
 ENDPROC(start_cpu0)
 #endif
 
-- 
2.4.3