Re: [PATCH 1/6] KVM: s390/vfio-ap: Use kvm_is_gpa_in_memslot() instead of open coded equivalent

[Anthony Krowiak]

On 7/29/25 1:42 PM, Sean Christopherson wrote:

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.

Signed-off-by: Sean Christopherson <sea...@google.com>

Acked-by: Anthony Krowiak <akrow...@linux.ibm.com>

I only reviewed this patch in the series.

---
  arch/s390/include/asm/kvm_host.h  | 2 ++
  arch/s390/kvm/priv.c              | 8 ++++++++
  drivers/s390/crypto/vfio_ap_ops.c | 2 +-
  3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index cb89e54ada25..449bc34e7cc3 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -719,6 +719,8 @@ bool kvm_s390_pv_cpu_is_protected(struct kvm_vcpu *vcpu);
  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) {}
diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
index 9253c70897a8..7773e1e323bc 100644
--- a/arch/s390/kvm/priv.c
+++ b/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_GPL_FOR_MODULES(kvm_s390_is_gpa_in_memslot, "vfio_ap");
+#endif
+
  /*
   * handle_pqap: Handling pqap interception
   * @vcpu: the vcpu having issue the pqap instruction
diff --git a/drivers/s390/crypto/vfio_ap_ops.c 
b/drivers/s390/crypto/vfio_ap_ops.c
index 766557547f83..eb5ff49f6fe7 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/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;