[[PATCH] v4 1/4] riscv: vector: refactor vector context operations

Lift riscv_v_{enable,disable} out of __*vstate_{save,restore,discard} so
that we can reuse some functions without repeatedly turning on/off
vector.

Also, refactor and document about the user context save in preempt_v to
make code more readable.

Signed-off-by: Andy Chiu <[email protected]>
---
Changelog v4:
 - fix an unused variable warning (Olof)
Changelog v3:
 - new patch since v3
---
 arch/riscv/include/asm/kvm_vcpu_vector.h |  8 +++++--
 arch/riscv/include/asm/vector.h          | 15 ++++++------
 arch/riscv/kernel/kernel_mode_vector.c   | 29 +++++++++++++++++++-----
 arch/riscv/kvm/vcpu_vector.c             |  8 +++----
 4 files changed, 41 insertions(+), 19 deletions(-)

diff --git a/arch/riscv/include/asm/kvm_vcpu_vector.h b/arch/riscv/include/asm/kvm_vcpu_vector.h
index 57a798a4cb0d..e679869e2ba3 100644
--- a/arch/riscv/include/asm/kvm_vcpu_vector.h
+++ b/arch/riscv/include/asm/kvm_vcpu_vector.h
@@ -16,14 +16,18 @@
 #include <asm/vector.h>
 #include <asm/kvm_host.h>
 
-static __always_inline void __kvm_riscv_vector_save(struct kvm_cpu_context *context)
+static __always_inline void kvm_riscv_vector_save(struct kvm_cpu_context *context)
 {
+	riscv_v_enable();
 	__riscv_v_vstate_save(&context->vector, context->vector.datap);
+	riscv_v_disable();
 }
 
-static __always_inline void __kvm_riscv_vector_restore(struct kvm_cpu_context *context)
+static __always_inline void kvm_riscv_vector_restore(struct kvm_cpu_context *context)
 {
+	riscv_v_enable();
 	__riscv_v_vstate_restore(&context->vector, context->vector.datap);
+	riscv_v_disable();
 }
 
 void kvm_riscv_vcpu_vector_reset(struct kvm_vcpu *vcpu);
diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h
index 00cb9c0982b1..45820cd900d6 100644
--- a/arch/riscv/include/asm/vector.h
+++ b/arch/riscv/include/asm/vector.h
@@ -198,7 +198,6 @@ static inline void __riscv_v_vstate_save(struct __riscv_v_ext_state *save_to,
 {
 	unsigned long vl;
 
-	riscv_v_enable();
 	__vstate_csr_save(save_to);
 	if (has_xtheadvector()) {
 		asm volatile (
@@ -227,7 +226,6 @@ static inline void __riscv_v_vstate_save(struct __riscv_v_ext_state *save_to,
 			".option pop\n\t"
 			: "=&r" (vl) : "r" (datap) : "memory");
 	}
-	riscv_v_disable();
 }
 
 static inline void __riscv_v_vstate_restore(struct __riscv_v_ext_state *restore_from,
@@ -235,7 +233,6 @@ static inline void __riscv_v_vstate_restore(struct __riscv_v_ext_state *restore_
 {
 	unsigned long vl;
 
-	riscv_v_enable();
 	if (has_xtheadvector()) {
 		asm volatile (
 			"mv t0, %0\n\t"
@@ -264,14 +261,12 @@ static inline void __riscv_v_vstate_restore(struct __riscv_v_ext_state *restore_
 			: "=&r" (vl) : "r" (datap) : "memory");
 	}
 	__vstate_csr_restore(restore_from);
-	riscv_v_disable();
 }
 
 static inline void __riscv_v_vstate_discard(void)
 {
 	unsigned long vl, vtype_inval = 1UL << (BITS_PER_LONG - 1);
 
-	riscv_v_enable();
 	if (has_xtheadvector())
 		asm volatile (THEAD_VSETVLI_T4X0E8M8D1 : : : "t4");
 	else
@@ -291,14 +286,14 @@ static inline void __riscv_v_vstate_discard(void)
 		"vsetvl		%0, x0, %1\n\t"
 		".option pop\n\t"
 		: "=&r" (vl) : "r" (vtype_inval));
-
-	riscv_v_disable();
 }
 
 static inline void riscv_v_vstate_discard(struct pt_regs *regs)
 {
 	if (riscv_v_vstate_query(regs)) {
+		riscv_v_enable();
 		__riscv_v_vstate_discard();
+		riscv_v_disable();
 		__riscv_v_vstate_dirty(regs);
 	}
 }
@@ -307,7 +302,9 @@ static inline void riscv_v_vstate_save(struct __riscv_v_ext_state *vstate,
 				       struct pt_regs *regs)
 {
 	if (__riscv_v_vstate_check(regs->status, DIRTY)) {
+		riscv_v_enable();
 		__riscv_v_vstate_save(vstate, vstate->datap);
+		riscv_v_disable();
 		__riscv_v_vstate_clean(regs);
 	}
 }
@@ -316,7 +313,9 @@ static inline void riscv_v_vstate_restore(struct __riscv_v_ext_state *vstate,
 					  struct pt_regs *regs)
 {
 	if (riscv_v_vstate_query(regs)) {
+		riscv_v_enable();
 		__riscv_v_vstate_restore(vstate, vstate->datap);
+		riscv_v_disable();
 		__riscv_v_vstate_clean(regs);
 	}
 }
@@ -378,8 +377,10 @@ static inline void __switch_to_vector(struct task_struct *prev,
 			prev->thread.riscv_v_flags |= RISCV_PREEMPT_V_IN_SCHEDULE;
 		}
 		if (riscv_preempt_v_dirty(prev)) {
+			riscv_v_enable();
 			__riscv_v_vstate_save(&prev->thread.kernel_vstate,
 					      prev->thread.kernel_vstate.datap);
+			riscv_v_disable();
 			riscv_preempt_v_clear_dirty(prev);
 		}
 	} else {
diff --git a/arch/riscv/kernel/kernel_mode_vector.c b/arch/riscv/kernel/kernel_mode_vector.c
index 99972a48e86b..21127b33fea8 100644
--- a/arch/riscv/kernel/kernel_mode_vector.c
+++ b/arch/riscv/kernel/kernel_mode_vector.c
@@ -123,7 +123,7 @@ static int riscv_v_stop_kernel_context(void)
 
 static int riscv_v_start_kernel_context(bool *is_nested)
 {
-	struct __riscv_v_ext_state *kvstate, *uvstate;
+	struct __riscv_v_ext_state *kvstate;
 
 	kvstate = &current->thread.kernel_vstate;
 	if (!kvstate->datap)
@@ -134,20 +134,35 @@ static int riscv_v_start_kernel_context(bool *is_nested)
 		*is_nested = true;
 		get_cpu_vector_context();
 		if (riscv_preempt_v_dirty(current)) {
+			riscv_v_enable();
 			__riscv_v_vstate_save(kvstate, kvstate->datap);
+			riscv_v_disable();
 			riscv_preempt_v_clear_dirty(current);
 		}
 		riscv_preempt_v_set_restore(current);
 		return 0;
 	}
 
-	/* Transfer the ownership of V from user to kernel, then save */
-	riscv_v_start(RISCV_PREEMPT_V | RISCV_PREEMPT_V_DIRTY);
+	/*
+	 * Skip saving user's context if it is not DIRTY. We would have to start KMV in "dirty" if
+	 * this check is performed after KMV starts, to protect user's ctx. Then, we could waste
+	 * time saving already "clean" context once KMV is started in "dirty".
+	 */
 	if (__riscv_v_vstate_check(task_pt_regs(current)->status, DIRTY)) {
-		uvstate = &current->thread.vstate;
-		__riscv_v_vstate_save(uvstate, uvstate->datap);
+		/* Transfer the ownership of V from user to kernel, then save */
+		riscv_v_start(RISCV_PREEMPT_V | RISCV_PREEMPT_V_DIRTY);
+		/*
+		 * Calling the guarded version of vstate_save to make the code cleaner. Also, the
+		 * vstate check within the call is necessary as context switch may happen between
+		 * __riscv_v_vstate_check and riscv_v_start. In such case we are not supposed to
+		 * save the context again.
+		 */
+		riscv_v_vstate_save(&current->thread.vstate, task_pt_regs(current));
+		riscv_preempt_v_clear_dirty(current);
+		return 0;
 	}
-	riscv_preempt_v_clear_dirty(current);
+
+	riscv_v_start(RISCV_PREEMPT_V);
 	return 0;
 }
 
@@ -180,7 +195,9 @@ asmlinkage void riscv_v_context_nesting_end(struct pt_regs *regs)
 	depth = riscv_v_ctx_get_depth();
 	if (depth == 0) {
 		if (riscv_preempt_v_restore(current)) {
+			riscv_v_enable();
 			__riscv_v_vstate_restore(vstate, vstate->datap);
+			riscv_v_disable();
 			__riscv_v_vstate_clean(regs);
 			riscv_preempt_v_reset_flags();
 		}
diff --git a/arch/riscv/kvm/vcpu_vector.c b/arch/riscv/kvm/vcpu_vector.c
index 62d2fb77bb9b..da6c6db846c1 100644
--- a/arch/riscv/kvm/vcpu_vector.c
+++ b/arch/riscv/kvm/vcpu_vector.c
@@ -46,7 +46,7 @@ void kvm_riscv_vcpu_guest_vector_save(struct kvm_cpu_context *cntx,
 {
 	if ((cntx->sstatus & SR_VS) == SR_VS_DIRTY) {
 		if (riscv_isa_extension_available(isa, v))
-			__kvm_riscv_vector_save(cntx);
+			kvm_riscv_vector_save(cntx);
 		kvm_riscv_vcpu_vector_clean(cntx);
 	}
 }
@@ -56,7 +56,7 @@ void kvm_riscv_vcpu_guest_vector_restore(struct kvm_cpu_context *cntx,
 {
 	if ((cntx->sstatus & SR_VS) != SR_VS_OFF) {
 		if (riscv_isa_extension_available(isa, v))
-			__kvm_riscv_vector_restore(cntx);
+			kvm_riscv_vector_restore(cntx);
 		kvm_riscv_vcpu_vector_clean(cntx);
 	}
 }
@@ -65,13 +65,13 @@ void kvm_riscv_vcpu_host_vector_save(struct kvm_cpu_context *cntx)
 {
 	/* No need to check host sstatus as it can be modified outside */
 	if (!kvm_riscv_isa_check_host(V))
-		__kvm_riscv_vector_save(cntx);
+		kvm_riscv_vector_save(cntx);
 }
 
 void kvm_riscv_vcpu_host_vector_restore(struct kvm_cpu_context *cntx)
 {
 	if (!kvm_riscv_isa_check_host(V))
-		__kvm_riscv_vector_restore(cntx);
+		kvm_riscv_vector_restore(cntx);
 }
 
 int kvm_riscv_vcpu_alloc_vector_context(struct kvm_vcpu *vcpu)
-- 
2.43.0


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