KVM: arm64: Prevent re-finalisation of pKVM for a given CPU

__pkvm_prot_finalize() completes the deprivilege of the host when pKVM
is in use by installing a stage-2 translation table for the calling CPU.

Issuing the hypercall multiple times for a given CPU makes little sense,
but in such a case just return early with -EPERM rather than go through
the whole page-table dance again.

Cc: Marc Zyngier <[email protected]>
Cc: Quentin Perret <[email protected]>
Signed-off-by: Will Deacon <[email protected]>
Signed-off-by: Marc Zyngier <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: willdeacon

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

@@ -123,6 +123,9 @@ int __pkvm_prot_finalize(void)
 	struct kvm_s2_mmu *mmu = &host_kvm.arch.mmu;
 	struct kvm_nvhe_init_params *params = this_cpu_ptr(&kvm_init_params);
 
+	if (params->hcr_el2 & HCR_VM)
+		return -EPERM;
+
 	params->vttbr = kvm_get_vttbr(mmu);
 	params->vtcr = host_kvm.arch.vtcr;
 	params->hcr_el2 |= HCR_VM;