[PATCH] riscv: vector: Check SR_SD before saving vstate

[Song Shuai]

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 at 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