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@kernel.org> Reviewed-by: Cyril Bur <cyrilbur@tenstorrent.com> Link: https://lore.kernel.org/r/20240720170659.1522-1-jszhang@kernel.orgSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

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@kernel.org> Reviewed-by: Cyril Bur <cyrilbur@tenstorrent.com> Link: https://lore.kernel.org/r/20240720170659.1522-1-jszhang@kernel.orgSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>
8f1534e7 · Jisheng Zhang · Palmer Dabbelt · 7e340f4f · 8f1534e7
Commit 8f1534e7 authored Jul 21, 2024 by Jisheng Zhang Committed by Palmer Dabbelt Sep 15, 2024
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arch/riscv/kernel/entry.S arch/riscv/kernel/entry.S +2 -2

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--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -326,8 +326,8 @@ SYM_CODE_START(ret_from_fork)
 	jalr s0
 1:
 	move a0, sp /* pt_regs */
-	la ra, ret_from_exception
+	call syscall_exit_to_user_mode
-	tail syscall_exit_to_user_mode
+	j ret_from_exception
 SYM_CODE_END(ret_from_fork)
 #ifdef CONFIG_IRQ_STACKS