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

tip-bot2 for Peter Zijlstra
2022-10-17T14:55:53Z

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@infradead.org>
AuthorDate: Thu, 15 Sep 2022 13:11:14 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
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@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111146.539578813@infradead.org
---
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)