[PATCH v7 6/6] riscv: KVM: do not save host vector context for vcpu

[Andy Chiu]

Host's vector contexts are already managed in per-thread's struct by
regular context switch routines. Saving and restoring the context in
preempt-notifier is redundant.

Signed-off-by: Andy Chiu <tchiu at tenstorrent.com>
---
Note: I haven't been able to get a statistically significant result on
how this help/regress KVM performance running a nginx server in guest.
I am happy to carry out a test again and post the number if there is any
suggestions on what workload can benefit from this, thanks!

Changelog v7:
 - new patch since v7
---
 arch/riscv/include/asm/kvm_vcpu_vector.h |  9 ++-------
 arch/riscv/kvm/vcpu.c                    |  3 +--
 arch/riscv/kvm/vcpu_vector.c             | 20 ++------------------
 3 files changed, 5 insertions(+), 27 deletions(-)

diff --git a/arch/riscv/include/asm/kvm_vcpu_vector.h b/arch/riscv/include/asm/kvm_vcpu_vector.h
index 60fa28030944..06409c870a06 100644
--- a/arch/riscv/include/asm/kvm_vcpu_vector.h
+++ b/arch/riscv/include/asm/kvm_vcpu_vector.h
@@ -35,8 +35,7 @@ void kvm_riscv_vcpu_guest_vector_save(struct kvm_cpu_context *cntx,
 				      unsigned long *isa);
 void kvm_riscv_vcpu_guest_vector_restore(struct kvm_cpu_context *cntx,
 					 unsigned long *isa);
-void kvm_riscv_vcpu_host_vector_save(struct kvm_cpu_context *cntx);
-void kvm_riscv_vcpu_host_vector_restore(struct kvm_cpu_context *cntx);
+void kvm_riscv_vcpu_host_vector_restore(void);
 int kvm_riscv_vcpu_alloc_vector_context(struct kvm_vcpu *vcpu);
 void kvm_riscv_vcpu_free_vector_context(struct kvm_vcpu *vcpu);
 void kvm_riscv_register_vctx_callback(void (*func)(void));
@@ -77,11 +76,7 @@ static inline void kvm_riscv_vcpu_guest_vector_restore(struct kvm_cpu_context *c
 {
 }
 
-static inline void kvm_riscv_vcpu_host_vector_save(struct kvm_cpu_context *cntx)
-{
-}
-
-static inline void kvm_riscv_vcpu_host_vector_restore(struct kvm_cpu_context *cntx)
+static inline void kvm_riscv_vcpu_host_vector_restore(void)
 {
 }
 
diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index caf6e0ad72ef..d9d31851ee62 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -650,7 +650,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	kvm_riscv_vcpu_guest_fp_restore(&vcpu->arch.guest_context,
 					vcpu->arch.isa);
 	get_cpu_vector_context();
-	kvm_riscv_vcpu_host_vector_save(&vcpu->arch.host_context);
 	kvm_riscv_vcpu_guest_vector_restore(&vcpu->arch.guest_context,
 					    vcpu->arch.isa);
 	put_cpu_vector_context();
@@ -677,7 +676,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 	get_cpu_vector_context();
 	kvm_riscv_vcpu_guest_vector_save(&vcpu->arch.guest_context,
 					 vcpu->arch.isa);
-	kvm_riscv_vcpu_host_vector_restore(&vcpu->arch.host_context);
+	kvm_riscv_vcpu_host_vector_restore();
 	put_cpu_vector_context();
 
 	if (kvm_riscv_nacl_available()) {
diff --git a/arch/riscv/kvm/vcpu_vector.c b/arch/riscv/kvm/vcpu_vector.c
index 730c32f7de50..6129a6e18404 100644
--- a/arch/riscv/kvm/vcpu_vector.c
+++ b/arch/riscv/kvm/vcpu_vector.c
@@ -61,17 +61,9 @@ void kvm_riscv_vcpu_guest_vector_restore(struct kvm_cpu_context *cntx,
 	}
 }
 
-void kvm_riscv_vcpu_host_vector_save(struct kvm_cpu_context *cntx)
+void kvm_riscv_vcpu_host_vector_restore(void)
 {
-	/* No need to check host sstatus as it can be modified outside */
-	if (!kvm_riscv_isa_check_host(V))
-		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);
+	riscv_v_vstate_set_restore(current, task_pt_regs(current));
 	riscv_v_flags_set(riscv_v_flags() & ~(RISCV_V_VCPU_CTX | RISCV_V_VCPU_NEED_RESTORE));
 }
 
@@ -81,20 +73,12 @@ int kvm_riscv_vcpu_alloc_vector_context(struct kvm_vcpu *vcpu)
 	if (!vcpu->arch.guest_context.vector.datap)
 		return -ENOMEM;
 
-	vcpu->arch.host_context.vector.datap = kzalloc(riscv_v_vsize, GFP_KERNEL_ACCOUNT);
-	if (!vcpu->arch.host_context.vector.datap) {
-		kfree(vcpu->arch.guest_context.vector.datap);
-		vcpu->arch.guest_context.vector.datap = NULL;
-		return -ENOMEM;
-	}
-
 	return 0;
 }
 
 void kvm_riscv_vcpu_free_vector_context(struct kvm_vcpu *vcpu)
 {
 	kfree(vcpu->arch.guest_context.vector.datap);
-	kfree(vcpu->arch.host_context.vector.datap);
 }
 
 void kvm_riscv_vcpu_flush_vector(void)
-- 
2.43.0