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

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Message-ID: <20250919003303.1355064-2-seanjc@google.com>
Date: Thu, 18 Sep 2025 17:32:59 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Madhavan Srinivasan <maddy@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>, 
	Janosch Frank <frankja@...ux.ibm.com>, Claudio Imbrenda <imbrenda@...ux.ibm.com>, 
	Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Vitaly Kuznetsov <vkuznets@...hat.com>, Tony Krowiak <akrowiak@...ux.ibm.com>, 
	Halil Pasic <pasic@...ux.ibm.com>, Jason Herne <jjherne@...ux.ibm.com>, 
	Harald Freudenberger <freude@...ux.ibm.com>, Holger Dengler <dengler@...ux.ibm.com>
Cc: linuxppc-dev@...ts.ozlabs.org, kvm@...r.kernel.org, 
	linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/5] 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 <akrowiak@...ux.ibm.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.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