[PATCH v2 2/3] riscv: vector: allow non-preemptible kernel-mode vector with IRQs off

[Andy Chiu]

Similar to commit 7137a203b251 ("arm64/fpsimd: Permit kernel mode NEON
with IRQs off"), we are upgrading get/put_cpu_vector_context such that
kvm_arch_vcpu_load/put can be safely called under both irq off and
regular process context.

Also, export both symbols so kvm module can call into it.

Signed-off-by: Andy Chiu <tchiu at tenstorrent.com>
---
Changelog v2:
 - new patch since v2
---
 arch/riscv/include/asm/simd.h          |  8 ++------
 arch/riscv/kernel/kernel_mode_vector.c | 18 ++++++++++++------
 2 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/arch/riscv/include/asm/simd.h b/arch/riscv/include/asm/simd.h
index adb50f3ec205..678c8b97cd49 100644
--- a/arch/riscv/include/asm/simd.h
+++ b/arch/riscv/include/asm/simd.h
@@ -44,12 +44,8 @@ static __must_check inline bool may_use_simd(void)
 		if (!riscv_preempt_v_started(current))
 			return true;
 	}
-	/*
-	 * Non-preemptible kernel-mode Vector temporarily disables bh. So we
-	 * must not return true on irq_disabled(). Otherwise we would fail the
-	 * lockdep check calling local_bh_enable()
-	 */
-	return !irqs_disabled() && !(riscv_v_flags() & RISCV_KERNEL_MODE_V);
+
+	return !(riscv_v_flags() & RISCV_KERNEL_MODE_V);
 }
 
 #else /* ! CONFIG_RISCV_ISA_V */
diff --git a/arch/riscv/kernel/kernel_mode_vector.c b/arch/riscv/kernel/kernel_mode_vector.c
index 307ac369c3d4..6627e1a82e19 100644
--- a/arch/riscv/kernel/kernel_mode_vector.c
+++ b/arch/riscv/kernel/kernel_mode_vector.c
@@ -55,13 +55,16 @@ void get_cpu_vector_context(void)
 	 * disable softirqs so it is impossible for softirqs to nest
 	 * get_cpu_vector_context() when kernel is actively using Vector.
 	 */
-	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
-		local_bh_disable();
-	else
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
+		if (!irqs_disabled())
+			local_bh_disable();
+	} else {
 		preempt_disable();
+	}
 
 	riscv_v_start(RISCV_KERNEL_MODE_V);
 }
+EXPORT_SYMBOL_GPL(get_cpu_vector_context);
 
 /*
  * Release the CPU vector context.
@@ -74,11 +77,14 @@ void put_cpu_vector_context(void)
 {
 	riscv_v_stop(RISCV_KERNEL_MODE_V);
 
-	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
-		local_bh_enable();
-	else
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
+		if (!irqs_disabled())
+			local_bh_enable();
+	} else {
 		preempt_enable();
+	}
 }
+EXPORT_SYMBOL_GPL(put_cpu_vector_context);
 
 #ifdef CONFIG_RISCV_ISA_V_PREEMPTIVE
 static __always_inline u32 *riscv_v_flags_ptr(void)
-- 
2.43.0