KVM: arm/arm64: vgic: Defer touching GICH_VMCR to vcpu_load/put

We don't have to save/restore the VMCR on every entry to/from the guest,
since on GICv2 we can access the control interface from EL1 and on VHE
systems with GICv3 we can access the control interface from KVM running
in EL2.

GICv3 systems without VHE becomes the rare case, which has to
save/restore the register on each round trip.

Note that userspace accesses may see out-of-date values if the VCPU is
running while accessing the VGIC state via the KVM device API, but this
is already the case and it is up to userspace to quiesce the CPUs before
reading the CPU registers from the GIC for an up-to-date view.

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

1 files changed, 20 insertions, 2 deletions

diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
index be0f4c3e0142..99213d744e4f 100644
--- a/virt/kvm/arm/vgic/vgic-v3.c
+++ b/virt/kvm/arm/vgic/vgic-v3.c
@@ -173,6 +173,7 @@ void vgic_v3_clear_lr(struct kvm_vcpu *vcpu, int lr)
 
 void vgic_v3_set_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcrp)
 {
+	struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
 	u32 vmcr;
 
 	/*
@@ -188,12 +189,15 @@ void vgic_v3_set_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcrp)
 	vmcr |= (vmcrp->grpen0 << ICH_VMCR_ENG0_SHIFT) & ICH_VMCR_ENG0_MASK;
 	vmcr |= (vmcrp->grpen1 << ICH_VMCR_ENG1_SHIFT) & ICH_VMCR_ENG1_MASK;
 
-	vcpu->arch.vgic_cpu.vgic_v3.vgic_vmcr = vmcr;
+	cpu_if->vgic_vmcr = vmcr;
 }
 
 void vgic_v3_get_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcrp)
 {
-	u32 vmcr = vcpu->arch.vgic_cpu.vgic_v3.vgic_vmcr;
+	struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
+	u32 vmcr;
+
+	vmcr = cpu_if->vgic_vmcr;
 
 	/*
 	 * Ignore the FIQen bit, because GIC emulation always implies
@@ -386,3 +390,17 @@ int vgic_v3_probe(const struct gic_kvm_info *info)
 
 	return 0;
 }
+
+void vgic_v3_load(struct kvm_vcpu *vcpu)
+{
+	struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
+
+	kvm_call_hyp(__vgic_v3_write_vmcr, cpu_if->vgic_vmcr);
+}
+
+void vgic_v3_put(struct kvm_vcpu *vcpu)
+{
+	struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
+
+	cpu_if->vgic_vmcr = kvm_call_hyp(__vgic_v3_read_vmcr);
+}