KVM: x86/mmu: Set kvm_page_fault.hva to KVM_HVA_ERR_BAD for "no slot" faults

Explicitly set fault->hva to KVM_HVA_ERR_BAD when handling a "no slot"
fault to ensure that KVM doesn't use a bogus virtual address, e.g. if
there *was* a slot but it's unusable (APIC access page), or if there
really was no slot, in which case fault->hva will be '0' (which is a
legal address for x86).

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Message-ID: <20240228024147.41573-15-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: sean-jc

arch/x86/kvm/mmu/mmu.c

@@ -3272,6 +3272,7 @@ static int kvm_handle_noslot_fault(struct kvm_vcpu *vcpu,
 	fault->slot = NULL;
 	fault->pfn = KVM_PFN_NOSLOT;
 	fault->map_writable = false;
+	fault->hva = KVM_HVA_ERR_BAD;
 
 	/*
 	 * If MMIO caching is disabled, emulate immediately without