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Tue, 07 Apr 2026 11:01:23 -0700 (PDT) Received: from [192.168.10.48] ([151.49.85.67]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43d1e4e56fesm49857921f8f.27.2026.04.07.11.01.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Apr 2026 11:01:19 -0700 (PDT) From: Paolo Bonzini To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Steffen Eiden , Alex Williamson Subject: [PATCH 2/3] KVM, vfio: remove symbol_get(kvm_get_kvm_safe) from vfio Date: Tue, 7 Apr 2026 20:01:06 +0200 Message-ID: <20260407180107.1603697-3-pbonzini@redhat.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260407180107.1603697-1-pbonzini@redhat.com> References: <20260407180107.1603697-1-pbonzini@redhat.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Right now, KVM and VFIO are using symbol_get to access each other's symbols because of a circular reference between the modules, as well as to avoid loading them unnecessarily. However, usage of symbol_get is mostly deprecated and there are just a handful of users left. In the case of VFIO, in particular, the functions it calls can be made inline. Start with kvm_get_kvm_safe, for which it is trivial to do so. While at it, move the function from kvm_host.h to kvm_types.h. Unlike e.g. drivers/s390/crypto/vfio_ap_ops.c, there's no need for VFIO to know any implementation details of KVM, and struct kvm can be treated as an opaque type. Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu/tdp_mmu.c | 2 +- arch/x86/kvm/vmx/nested.h | 4 ++-- drivers/vfio/vfio_main.c | 8 +------- include/linux/kvm_host.h | 8 ++++---- include/linux/kvm_types.h | 22 ++++++++++++++++++++++ virt/kvm/kvm_main.c | 27 ++++++--------------------- 6 files changed, 36 insertions(+), 35 deletions(-) diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 9c26038f6b77..a88686b5db24 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -1136,7 +1136,7 @@ void kvm_tdp_mmu_invalidate_roots(struct kvm *kvm, * being destroyed in an error path of KVM_CREATE_VM. */ if (IS_ENABLED(CONFIG_PROVE_LOCKING) && - refcount_read(&kvm->users_count) && kvm->created_vcpus) + refcount_read(&kvm->rc.users_count) && kvm->created_vcpus) lockdep_assert_held_write(&kvm->mmu_lock); /* diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h index 213a448104af..2c83fc905698 100644 --- a/arch/x86/kvm/vmx/nested.h +++ b/arch/x86/kvm/vmx/nested.h @@ -58,7 +58,7 @@ bool nested_vmx_check_io_bitmaps(struct kvm_vcpu *vcpu, unsigned int port, static inline struct vmcs12 *get_vmcs12(struct kvm_vcpu *vcpu) { lockdep_assert_once(lockdep_is_held(&vcpu->mutex) || - !refcount_read(&vcpu->kvm->users_count)); + !refcount_read(&vcpu->kvm->rc.users_count)); return to_vmx(vcpu)->nested.cached_vmcs12; } @@ -66,7 +66,7 @@ static inline struct vmcs12 *get_vmcs12(struct kvm_vcpu *vcpu) static inline struct vmcs12 *get_shadow_vmcs12(struct kvm_vcpu *vcpu) { lockdep_assert_once(lockdep_is_held(&vcpu->mutex) || - !refcount_read(&vcpu->kvm->users_count)); + !refcount_read(&vcpu->kvm->rc.users_count)); return to_vmx(vcpu)->nested.cached_shadow_vmcs12; } diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c index d1bbc42d484a..cb6eaabd64ce 100644 --- a/drivers/vfio/vfio_main.c +++ b/drivers/vfio/vfio_main.c @@ -436,7 +436,6 @@ EXPORT_SYMBOL_GPL(vfio_unregister_group_dev); void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm, struct module *kvm_module) { void (*pfn)(struct kvm *kvm); - bool (*fn)(struct kvm *kvm); bool ret; lockdep_assert_held(&device->dev_set->lock); @@ -451,12 +450,7 @@ void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm, struc if (WARN_ON(!pfn)) goto out_put_mod; - fn = symbol_get(kvm_get_kvm_safe); - if (WARN_ON(!fn)) - goto out_put_sym; - - ret = fn(kvm); - symbol_put(kvm_get_kvm_safe); + ret = kvm_get_kvm_safe(kvm); if (!ret) goto out_put_sym; diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 6b76e7a6f4c2..5163b541c82d 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -767,6 +767,9 @@ struct kvm_memslots { }; struct kvm { + /* Must be the first field, see function definitions in kvm_types.h. */ + struct kvm_refcount rc; + #ifdef KVM_HAVE_MMU_RWLOCK rwlock_t mmu_lock; #else @@ -830,7 +833,6 @@ struct kvm { struct list_head ioeventfds; struct kvm_vm_stat stat; struct kvm_arch arch; - refcount_t users_count; #ifdef CONFIG_KVM_MMIO struct kvm_coalesced_mmio_ring *coalesced_mmio_ring; spinlock_t ring_lock; @@ -1062,8 +1064,6 @@ static inline void kvm_irqfd_exit(void) int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module); void kvm_exit(void); -void kvm_get_kvm(struct kvm *kvm); -bool kvm_get_kvm_safe(struct kvm *kvm); void kvm_put_kvm(struct kvm *kvm); bool file_is_kvm(struct file *file); void kvm_put_kvm_no_destroy(struct kvm *kvm); @@ -1073,7 +1073,7 @@ static inline struct kvm_memslots *__kvm_memslots(struct kvm *kvm, int as_id) as_id = array_index_nospec(as_id, KVM_MAX_NR_ADDRESS_SPACES); return srcu_dereference_check(kvm->memslots[as_id], &kvm->srcu, lockdep_is_held(&kvm->slots_lock) || - !refcount_read(&kvm->users_count)); + !refcount_read(&kvm->rc.users_count)); } static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm) diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h index a568d8e6f4e8..4cb68c71a13c 100644 --- a/include/linux/kvm_types.h +++ b/include/linux/kvm_types.h @@ -33,6 +33,7 @@ #include #include +#include struct kvm; struct kvm_async_pf; @@ -140,6 +141,27 @@ struct kvm_vcpu_stat_generic { }; #define KVM_STATS_NAME_SIZE 48 + +struct kvm_refcount { + refcount_t users_count; +}; + +static inline void kvm_get_kvm(struct kvm *kvm) +{ + struct kvm_refcount *rc = (struct kvm_refcount *)kvm; + refcount_inc(&rc->users_count); +} + +/* + * A safe version of kvm_get_kvm(), making sure the vm is not being destroyed. + * Return true if kvm referenced successfully, false otherwise. + */ +static inline bool kvm_get_kvm_safe(struct kvm *kvm) +{ + struct kvm_refcount *rc = (struct kvm_refcount *)kvm; + return refcount_inc_not_zero(&rc->users_count); +} + #endif /* !__ASSEMBLER__ */ #endif /* __KVM_TYPES_H__ */ diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 9093251beb39..6e3796814da7 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1099,7 +1099,7 @@ static inline struct kvm_io_bus *kvm_get_bus_for_destruction(struct kvm *kvm, enum kvm_bus idx) { return rcu_dereference_protected(kvm->buses[idx], - !refcount_read(&kvm->users_count)); + !refcount_read(&kvm->rc.users_count)); } static struct kvm *kvm_create_vm(unsigned long type, const char *fdname) @@ -1153,7 +1153,8 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname) if (r) goto out_err_no_irq_routing; - refcount_set(&kvm->users_count, 1); + BUILD_BUG_ON(offsetof(struct kvm, rc) != 0); + refcount_set(&kvm->rc.users_count, 1); for (i = 0; i < kvm_arch_nr_memslot_as_ids(kvm); i++) { for (j = 0; j < 2; j++) { @@ -1223,7 +1224,7 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname) out_err_no_disable: kvm_arch_destroy_vm(kvm); out_err_no_arch_destroy_vm: - WARN_ON_ONCE(!refcount_dec_and_test(&kvm->users_count)); + WARN_ON_ONCE(!refcount_dec_and_test(&kvm->rc.users_count)); for (i = 0; i < KVM_NR_BUSES; i++) kfree(kvm_get_bus_for_destruction(kvm, i)); kvm_free_irq_routing(kvm); @@ -1316,25 +1317,9 @@ static void kvm_destroy_vm(struct kvm *kvm) mmdrop(mm); } -void kvm_get_kvm(struct kvm *kvm) -{ - refcount_inc(&kvm->users_count); -} -EXPORT_SYMBOL_GPL(kvm_get_kvm); - -/* - * Make sure the vm is not during destruction, which is a safe version of - * kvm_get_kvm(). Return true if kvm referenced successfully, false otherwise. - */ -bool kvm_get_kvm_safe(struct kvm *kvm) -{ - return refcount_inc_not_zero(&kvm->users_count); -} -EXPORT_SYMBOL_GPL(kvm_get_kvm_safe); - void kvm_put_kvm(struct kvm *kvm) { - if (refcount_dec_and_test(&kvm->users_count)) + if (refcount_dec_and_test(&kvm->rc.users_count)) kvm_destroy_vm(kvm); } EXPORT_SYMBOL_GPL(kvm_put_kvm); @@ -1348,7 +1333,7 @@ EXPORT_SYMBOL_GPL(kvm_put_kvm); */ void kvm_put_kvm_no_destroy(struct kvm *kvm) { - WARN_ON(refcount_dec_and_test(&kvm->users_count)); + WARN_ON(refcount_dec_and_test(&kvm->rc.users_count)); } EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_put_kvm_no_destroy); -- 2.53.0