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From: Song Shuai <songshuaishuai@tinylab.org>
To: paul.walmsley@sifive.com,
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Cc: linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH] riscv: vector: Check SR_SD before saving vstate
Date: Thu, 21 Dec 2023 15:04:49 +0800
Message-Id: <20231221070449.1809020-1-songshuaishuai@tinylab.org>
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The SD bit summarizes the dirty states of FS, VS, or XS fields,
providing a "fast check" before saving fstate or vstate.

Let __switch_to_vector() check SD bit as __switch_to_fpu() does.

Fixes: 3a2df6323def ("riscv: Add task switch support for vector")
Signed-off-by: Song Shuai <songshuaishuai@tinylab.org>
---
 arch/riscv/include/asm/vector.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h
index 87aaef656257..d30fa56f67c6 100644
--- a/arch/riscv/include/asm/vector.h
+++ b/arch/riscv/include/asm/vector.h
@@ -190,7 +190,8 @@ static inline void __switch_to_vector(struct task_struct *prev,
 	struct pt_regs *regs;
 
 	regs = task_pt_regs(prev);
-	riscv_v_vstate_save(prev, regs);
+	if (unlikely(regs->status & SR_SD))
+		riscv_v_vstate_save(prev, regs);
 	riscv_v_vstate_restore(next, task_pt_regs(next));
 }
 
-- 
2.20.1