KVM: arm64: Track value of cptr_el2 in struct kvm_vcpu_arch

Track the baseline guest value for cptr_el2 in struct
kvm_vcpu_arch, similar to the other registers that control traps.
Use this value when setting cptr_el2 for the guest.

Currently this value is unchanged (CPTR_EL2_DEFAULT), but future
patches will set trapping bits based on features supported for
the guest.

No functional change intended.
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210817081134.2918285-9-tabba@google.com

arch/arm64/include/asm/kvm_host.h

@@ -290,6 +290,7 @@ struct kvm_vcpu_arch {
 	/* Values of trap registers for the guest. */
 	u64 hcr_el2;
 	u64 mdcr_el2;
+	u64 cptr_el2;
 
 	/* Values of trap registers for the host before guest entry. */
 	u64 mdcr_el2_host;

arch/arm64/kvm/arm.c

@@ -1104,6 +1104,7 @@ static int kvm_arch_vcpu_ioctl_vcpu_init(struct kvm_vcpu *vcpu,
 	}
 
 	vcpu_reset_hcr(vcpu);
+	vcpu->arch.cptr_el2 = CPTR_EL2_DEFAULT;
 
 	/*
 	 * Handle the "start in power-off" case.

arch/arm64/kvm/hyp/nvhe/switch.c

@@ -41,7 +41,7 @@ static void __activate_traps(struct kvm_vcpu *vcpu)
 	___activate_traps(vcpu);
 	__activate_traps_common(vcpu);
 
-	val = CPTR_EL2_DEFAULT;
+	val = vcpu->arch.cptr_el2;
 	val |= CPTR_EL2_TTA | CPTR_EL2_TAM;
 	if (!update_fp_enabled(vcpu)) {
 		val |= CPTR_EL2_TFP | CPTR_EL2_TZ;