KVM: arm/arm64: vgic: Improve sync_hwstate performance

There is no need to call any functions to fold LRs when we don't use any
LRs and we don't need to mess with overflow flags, take spinlocks, or
prune the AP list if the AP list is empty.

Note: list_empty is a single atomic read (uses READ_ONCE) and can
therefore check if a list is empty or not without the need to take the
spinlock protecting the list.

Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@linaro.org>

diff --git a/virt/kvm/arm/vgic/vgic-v2.c b/virt/kvm/arm/vgic/vgic-v2.c
index b58b086d8d076801f12544dd8fb8b68e206d430f..025b57d5787edabb568ff1415eb1fdc6c6e262d5 100644 (file)
--- a/virt/kvm/arm/vgic/vgic-v2.c
+++ b/virt/kvm/arm/vgic/vgic-v2.c
@@ -44,12 +44,13 @@ static bool lr_signals_eoi_mi(u32 lr_val)
  */
 void vgic_v2_fold_lr_state(struct kvm_vcpu *vcpu)
 {
-       struct vgic_v2_cpu_if *cpuif = &vcpu->arch.vgic_cpu.vgic_v2;
+       struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
+       struct vgic_v2_cpu_if *cpuif = &vgic_cpu->vgic_v2;
        int lr;
 
        cpuif->vgic_hcr &= ~GICH_HCR_UIE;
 
-       for (lr = 0; lr < vcpu->arch.vgic_cpu.used_lrs; lr++) {
+       for (lr = 0; lr < vgic_cpu->used_lrs; lr++) {
                u32 val = cpuif->vgic_lr[lr];
                u32 intid = val & GICH_LR_VIRTUALID;
                struct vgic_irq *irq;
@@ -91,6 +92,8 @@ void vgic_v2_fold_lr_state(struct kvm_vcpu *vcpu)
                spin_unlock(&irq->irq_lock);
                vgic_put_irq(vcpu->kvm, irq);
        }
+
+       vgic_cpu->used_lrs = 0;
 }
 
 /*

diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
index 4f2dce68660011405d1ccb1b8aef1c55d7a77306..bc7010db9f4d36d752939e2c29535e231035a810 100644 (file)
--- a/virt/kvm/arm/vgic/vgic-v3.c
+++ b/virt/kvm/arm/vgic/vgic-v3.c
@@ -36,13 +36,14 @@ static bool lr_signals_eoi_mi(u64 lr_val)
 
 void vgic_v3_fold_lr_state(struct kvm_vcpu *vcpu)
 {
-       struct vgic_v3_cpu_if *cpuif = &vcpu->arch.vgic_cpu.vgic_v3;
+       struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
+       struct vgic_v3_cpu_if *cpuif = &vgic_cpu->vgic_v3;
        u32 model = vcpu->kvm->arch.vgic.vgic_model;
        int lr;
 
        cpuif->vgic_hcr &= ~ICH_HCR_UIE;
 
-       for (lr = 0; lr < vcpu->arch.vgic_cpu.used_lrs; lr++) {
+       for (lr = 0; lr < vgic_cpu->used_lrs; lr++) {
                u64 val = cpuif->vgic_lr[lr];
                u32 intid;
                struct vgic_irq *irq;
@@ -92,6 +93,8 @@ void vgic_v3_fold_lr_state(struct kvm_vcpu *vcpu)
                spin_unlock(&irq->irq_lock);
                vgic_put_irq(vcpu->kvm, irq);
        }
+
+       vgic_cpu->used_lrs = 0;
 }
 
 /* Requires the irq to be locked already */

diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
index 04a405ad562280b426c88073ada94237772f1ac8..3d0979c307212cd1f17f3aec9295bb150bf64c1b 100644 (file)
--- a/virt/kvm/arm/vgic/vgic.c
+++ b/virt/kvm/arm/vgic/vgic.c
@@ -633,11 +633,13 @@ void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
 {
        struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
 
-       vgic_fold_lr_state(vcpu);
-       vgic_prune_ap_list(vcpu);
+       /* An empty ap_list_head implies used_lrs == 0 */
+       if (list_empty(&vcpu->arch.vgic_cpu.ap_list_head))
+               return;
 
-       /* Make sure we can fast-path in flush_hwstate */
-       vgic_cpu->used_lrs = 0;
+       if (vgic_cpu->used_lrs)
+               vgic_fold_lr_state(vcpu);
+       vgic_prune_ap_list(vcpu);
 }
 
 /* Flush our emulation state into the GIC hardware before entering the guest. */