[tip: x86/core] x86/entry: Make sync_regs() invocation a tail call

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     ef79ed20e3ae9ee9ac2e0f3a4e12814893972e63
Gitweb:        https://git.kernel.org/tip/ef79ed20e3ae9ee9ac2e0f3a4e12814893972e63
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Thu, 15 Sep 2022 13:11:14 +02:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 17 Oct 2022 16:41:09 +02:00

x86/entry: Make sync_regs() invocation a tail call

No point in having a call there. Spare the call/ret overhead.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220915111146.539578813@xxxxxxxxxxxxx
---
 arch/x86/entry/entry_64.S | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 5c578a7..b24b84b 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1062,11 +1062,8 @@ SYM_CODE_START_LOCAL(error_entry)
 	UNTRAIN_RET
 
 	leaq	8(%rsp), %rdi			/* arg0 = pt_regs pointer */
-.Lerror_entry_from_usermode_after_swapgs:
-
 	/* Put us onto the real thread stack. */
-	call	sync_regs
-	RET
+	jmp	sync_regs
 
 	/*
 	 * There are two places in the kernel that can potentially fault with
@@ -1124,7 +1121,7 @@ SYM_CODE_START_LOCAL(error_entry)
 	leaq	8(%rsp), %rdi			/* arg0 = pt_regs pointer */
 	call	fixup_bad_iret
 	mov	%rax, %rdi
-	jmp	.Lerror_entry_from_usermode_after_swapgs
+	jmp	sync_regs
 SYM_CODE_END(error_entry)
 
 SYM_CODE_START_LOCAL(error_return)