[PATCH 1/3] riscv: vector: Check the xtheadvector status field in riscv_v_is_on()

[Gleb Pesin via B4 Relay <devnull+dormancygrace.gmail.com@kernel.org>]

From: Gleb Pesin <dormancygrace@gmail.com>

riscv_v_is_on() tests only the standard sstatus.VS field. Since commit
d863910eabaf ("riscv: vector: Support xtheadvector save/restore"),
riscv_v_enable() and riscv_v_disable() set and clear SR_VS_THEAD instead
on cores with xtheadvector, so riscv_v_is_on() returns false there even
while the vector unit is enabled.

__switch_to_vector() relies on riscv_v_is_on() to recognise a task that
is switched out inside a preemptible kernel-mode vector section. On
xtheadvector cores that check never succeeds: the outgoing task neither
disables the vector unit nor sets RISCV_PREEMPT_V_IN_SCHEDULE, and
riscv_v_enable() is skipped when the task is switched back in.

Test the status field that the running core actually uses.

Fixes: d863910eabaf ("riscv: vector: Support xtheadvector save/restore")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Gleb Pesin <dormancygrace@gmail.com>
---
 arch/riscv/include/asm/vector.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h
index fffe72a77..910313dd0 100644
--- a/arch/riscv/include/asm/vector.h
+++ b/arch/riscv/include/asm/vector.h
@@ -128,7 +128,9 @@ static __always_inline void riscv_v_disable(void)
 
 static __always_inline bool riscv_v_is_on(void)
 {
-	return !!(csr_read(CSR_SSTATUS) & SR_VS);
+	unsigned long mask = has_xtheadvector() ? SR_VS_THEAD : SR_VS;
+
+	return !!(csr_read(CSR_SSTATUS) & mask);
 }
 
 static __always_inline void __vstate_csr_save(struct __riscv_v_ext_state *dest)

-- 
2.53.0