linux-kernel - [PATCH v3 05/23] KVM: s390: Enable KVM_GENERIC_MMU

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Message-ID: <20251106161117.350395-6-imbrenda@linux.ibm.com>
Date: Thu,  6 Nov 2025 17:10:59 +0100
From: Claudio Imbrenda <imbrenda@...ux.ibm.com>
To: kvm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        borntraeger@...ibm.com, frankja@...ux.ibm.com, nsg@...ux.ibm.com,
        nrb@...ux.ibm.com, seiden@...ux.ibm.com, schlameuss@...ux.ibm.com,
        hca@...ux.ibm.com, svens@...ux.ibm.com, agordeev@...ux.ibm.com,
        gor@...ux.ibm.com, david@...hat.com, gerald.schaefer@...ux.ibm.com
Subject: [PATCH v3 05/23] KVM: s390: Enable KVM_GENERIC_MMU_NOTIFIER

Enable KVM_GENERIC_MMU_NOTIFIER, for now with empty placeholder callbacks.

Also enable KVM_MMU_LOCKLESS_AGING and define KVM_HAVE_MMU_RWLOCK.

Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@...ux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@...ux.ibm.com>
---
 arch/s390/include/asm/kvm_host.h |  1 +
 arch/s390/kvm/Kconfig            |  3 ++-
 arch/s390/kvm/kvm-s390.c         | 45 +++++++++++++++++++++++++++++++-
 3 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index c2ba3d4398c5..f5f87dae0dd9 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -27,6 +27,7 @@
 #include <asm/isc.h>
 #include <asm/guarded_storage.h>
 
+#define KVM_HAVE_MMU_RWLOCK
 #define KVM_MAX_VCPUS 255
 
 #define KVM_INTERNAL_MEM_SLOTS 1
diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig
index cae908d64550..e86332b26511 100644
--- a/arch/s390/kvm/Kconfig
+++ b/arch/s390/kvm/Kconfig
@@ -29,7 +29,8 @@ config KVM
 	select HAVE_KVM_INVALID_WAKEUPS
 	select HAVE_KVM_NO_POLL
 	select KVM_VFIO
-	select MMU_NOTIFIER
+	select KVM_GENERIC_MMU_NOTIFIER
+	select KVM_MMU_LOCKLESS_AGING
 	help
 	  Support hosting paravirtualized guest machines using the SIE
 	  virtualization capability on the mainframe. This should work
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 16ba04062854..2e34f993e3c5 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -4918,7 +4918,7 @@ int __kvm_s390_handle_dat_fault(struct kvm_vcpu *vcpu, gfn_t gfn, gpa_t gaddr, u
 	rc = fixup_user_fault(vcpu->arch.gmap->mm, vmaddr, fault_flags, &unlocked);
 	if (!rc)
 		rc = __gmap_link(vcpu->arch.gmap, gaddr, vmaddr);
-	scoped_guard(spinlock, &vcpu->kvm->mmu_lock) {
+	scoped_guard(read_lock, &vcpu->kvm->mmu_lock) {
 		kvm_release_faultin_page(vcpu->kvm, page, false, writable);
 	}
 	mmap_read_unlock(vcpu->arch.gmap->mm);
@@ -6125,6 +6125,49 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 	return;
 }
 
+/**
+ * kvm_test_age_gfn() - test young
+ * @kvm: the kvm instance
+ * @range: the range of guest addresses whose young status needs to be cleared
+ *
+ * Context: called by KVM common code without holding the kvm mmu lock
+ * Return: true if any page in the given range is young, otherwise 0.
+ */
+bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
+{
+	return false;
+}
+
+/**
+ * kvm_age_gfn() - clear young
+ * @kvm: the kvm instance
+ * @range: the range of guest addresses whose young status needs to be cleared
+ *
+ * Context: called by KVM common code without holding the kvm mmu lock
+ * Return: true if any page in the given range was young, otherwise 0.
+ */
+bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
+{
+	return false;
+}
+
+/**
+ * kvm_unmap_gfn_range() - Unmap a range of guest addresses
+ * @kvm: the kvm instance
+ * @range: the range of guest page frames to invalidate
+ *
+ * This function always returns false because every DAT table modification
+ * has to use the appropriate DAT table manipulation instructions, which will
+ * keep the TLB coherent, hence no additional TLB flush is ever required.
+ *
+ * Context: called by KVM common code with the kvm mmu write lock held
+ * Return: false
+ */
+bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
+{
+	return false;
+}
+
 static inline unsigned long nonhyp_mask(int i)
 {
 	unsigned int nonhyp_fai = (sclp.hmfai << i * 2) >> 30;
-- 
2.51.1