linux-kernel - [RFC PATCH v3 24/32] x86/fred: let ret_from_fork() jmp to fred_exit

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Date:   Thu, 23 Feb 2023 23:01:37 -0800
From:   Xin Li <xin3.li@...el.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, peterz@...radead.org,
        andrew.cooper3@...rix.com, seanjc@...gle.com, pbonzini@...hat.com,
        ravi.v.shankar@...el.com
Subject: [RFC PATCH v3 24/32] x86/fred: let ret_from_fork() jmp to fred_exit_user when FRED is enabled

From: "H. Peter Anvin (Intel)" <hpa@...or.com>

Let ret_from_fork() jmp to fred_exit_user when FRED is enabled,
otherwise the existing IDT code is chosen.

Signed-off-by: H. Peter Anvin (Intel) <hpa@...or.com>
Signed-off-by: Xin Li <xin3.li@...el.com>
---
 arch/x86/entry/entry_64.S | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 7ecd2aeeeffc..7ffd20578b8c 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -299,7 +299,12 @@ SYM_CODE_START_NOALIGN(ret_from_fork)
 	UNWIND_HINT_REGS
 	movq	%rsp, %rdi
 	call	syscall_exit_to_user_mode	/* returns with IRQs disabled */
+#ifdef CONFIG_X86_FRED
+	ALTERNATIVE "jmp swapgs_restore_regs_and_return_to_usermode", \
+		    "jmp fred_exit_user", X86_FEATURE_FRED
+#else
 	jmp	swapgs_restore_regs_and_return_to_usermode
+#endif
 
 1:
 	/* kernel thread */
-- 
2.34.1