KVM: s390/vfio-ap: Use kvm_is_gpa_in_memslot() instead of open coded equivalent

Use kvm_is_gpa_in_memslot() to check the validity of the notification
indicator byte address instead of open coding equivalent logic in the VFIO
AP driver.

Opportunistically use a dedicated wrapper that exists and is exported
expressly for the VFIO AP module.  kvm_is_gpa_in_memslot() is generally
unsuitable for use outside of KVM; other drivers typically shouldn't rely
on KVM's memslots, and using the API requires kvm->srcu (or slots_lock) to
be held for the entire duration of the usage, e.g. to avoid TOCTOU bugs.
handle_pqap() is a bit of a special case, as it's explicitly invoked from
KVM with kvm->srcu already held, and the VFIO AP driver is in many ways an
extension of KVM that happens to live in a separate module.

Providing a dedicated API for the VFIO AP driver will allow restricting
the vast majority of generic KVM's exports to KVM submodules (e.g. to x86's
kvm-{amd,intel}.ko vendor mdoules).

No functional change intended.

Acked-by: Anthony Krowiak <[email protected]>
Reviewed-by: Christian Borntraeger <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

Author: sean-jc

arch/s390/include/asm/kvm_host.h

@@ -722,6 +722,8 @@ extern int kvm_s390_enter_exit_sie(struct kvm_s390_sie_block *scb,
 extern int kvm_s390_gisc_register(struct kvm *kvm, u32 gisc);
 extern int kvm_s390_gisc_unregister(struct kvm *kvm, u32 gisc);
 
+bool kvm_s390_is_gpa_in_memslot(struct kvm *kvm, gpa_t gpa);
+
 static inline void kvm_arch_free_memslot(struct kvm *kvm,
 					 struct kvm_memory_slot *slot) {}
 static inline void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen) {}

arch/s390/kvm/priv.c

@@ -605,6 +605,14 @@ static int handle_io_inst(struct kvm_vcpu *vcpu)
 	}
 }
 
+#if IS_ENABLED(CONFIG_VFIO_AP)
+bool kvm_s390_is_gpa_in_memslot(struct kvm *kvm, gpa_t gpa)
+{
+	return kvm_is_gpa_in_memslot(kvm, gpa);
+}
+EXPORT_SYMBOL_FOR_MODULES(kvm_s390_is_gpa_in_memslot, "vfio_ap");
+#endif
+
 /*
  * handle_pqap: Handling pqap interception
  * @vcpu: the vcpu having issue the pqap instruction

drivers/s390/crypto/vfio_ap_ops.c

@@ -354,7 +354,7 @@ static int vfio_ap_validate_nib(struct kvm_vcpu *vcpu, dma_addr_t *nib)
 
 	if (!*nib)
 		return -EINVAL;
-	if (kvm_is_error_hva(gfn_to_hva(vcpu->kvm, *nib >> PAGE_SHIFT)))
+	if (!kvm_s390_is_gpa_in_memslot(vcpu->kvm, *nib))
 		return -EINVAL;
 
 	return 0;