linux-kernel - [PATCH v2] riscv: avoid Imbalance in RAS

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Message-ID: <20240720170659.1522-1-jszhang@kernel.org>
Date: Sun, 21 Jul 2024 01:06:59 +0800
From: Jisheng Zhang <jszhang@...nel.org>
To: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>
Cc: linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Cyril Bur <cyrilbur@...storrent.com>
Subject: [PATCH v2] riscv: avoid Imbalance in RAS

Inspired by[1], modify the code to remove the code of modifying ra to
avoid imbalance RAS (return address stack) which may lead to incorret
predictions on return.

Link: https://lore.kernel.org/linux-riscv/20240607061335.2197383-1-cyrilbur@tenstorrent.com/ [1]
Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
Reviewed-by: Cyril Bur <cyrilbur@...storrent.com>
---

since v1:
 - make it a seperate patch
 - modify the commit msg, thank Deepak
 - collect Reviewed-by tag

 arch/riscv/kernel/entry.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index c933460ed3e9..81dec627a8d4 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -235,8 +235,8 @@ SYM_CODE_START(ret_from_fork)
 	jalr s0
 1:
 	move a0, sp /* pt_regs */
-	la ra, ret_from_exception
-	tail syscall_exit_to_user_mode
+	call syscall_exit_to_user_mode
+	j ret_from_exception
 SYM_CODE_END(ret_from_fork)
 
 #ifdef CONFIG_IRQ_STACKS
-- 
2.43.0