[PATCH v2 1/5] KVM: s390/vfio-ap: Use kvm_is_gpa_in_memslot() instead of open coded equivalent

Sean Christopherson
2025-09-19T00:33:16Z

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 <akrowiak@linux.ibm.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
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 f870d09515cc..ee25eeda12fd 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/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) {}
diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
index 9253c70897a8..9a71b6e00948 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_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;
--
2.51.0.470.ga7dc726c21-goog