linux-kernel - [RFC 07/17] x86/asm/64: Merge the fast and slow SYSRET paths

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Date:   Wed,  6 Sep 2017 14:36:52 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: [RFC 07/17] x86/asm/64: Merge the fast and slow SYSRET paths

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/entry/entry_64.S | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 45d4cb8fd81b..a9e318f7cc9b 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -216,9 +216,8 @@ entry_SYSCALL_64_fastpath:
 	TRACE_IRQS_ON		/* user mode is traced as IRQs on */
 	movq	RIP(%rsp), %rcx
 	movq	EFLAGS(%rsp), %r11
-	RESTORE_C_REGS_EXCEPT_RCX_R11
-	movq	RSP(%rsp), %rsp
-	USERGS_SYSRET64
+	addq	$6*8, %rsp
+	jmp	.Lpop_c_regs_and_sysret
 
 1:
 	/*
@@ -309,6 +308,7 @@ return_from_SYSCALL_64:
 syscall_return_via_sysret:
 	/* rcx and r11 are already restored (see code above) */
 	POP_EXTRA_REGS
+.Lpop_c_regs_and_sysret:
 	popq	%rsi	/* skip r11 */
 	popq	%r10
 	popq	%r9
-- 
2.13.5