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Thu, 2 Apr 2026 04:21:26 +0000 (GMT) From: Steffen Eiden To: kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org Cc: Andreas Grapentin , Arnd Bergmann , Catalin Marinas , Christian Borntraeger , Claudio Imbrenda , David Hildenbrand , Gautam Gala , Hendrik Brueckner , Janosch Frank , Joey Gouly , Marc Zyngier , Nina Schoetterl-Glausch , Oliver Upton , Paolo Bonzini , Suzuki K Poulose , Ulrich Weigand , Will Deacon , Zenghui Yu Subject: [PATCH v1 02/27] KVM, vfio: remove symbol_get(kvm_get_kvm_safe) from vfio Date: Thu, 2 Apr 2026 06:20:58 +0200 Message-ID: <20260402042125.3948963-3-seiden@linux.ibm.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260402042125.3948963-1-seiden@linux.ibm.com> References: <20260402042125.3948963-1-seiden@linux.ibm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=J6enLQnS c=1 sm=1 tr=0 ts=69cdeecb cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=20KFwNOVAAAA:8 a=VnNF1IyMAAAA:8 a=VFmQUFSrCZiC7oI7mJkA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDAyMDAzNCBTYWx0ZWRfX7pOq5HtFrfSz YCmmDxJdORVt5YVAJv3a9HnJc0W0yIBMW/Fys8yXignuutF1vpvstnPbdfO2xQibJkkbh6OZi82 C8Qx/pF5iIN4CoLxZpJZSFZr/zV8HMGkK24GQbQzapR0VK6aMjGbCyc5HVacTO6WHmeP8e18dJA b/wHIKAMJvuQYfe2Gr8Hsd8TaHs4EJATbxty0PFA3AT9jlaIJFZTgkKXFtAl7vXJ/Qa7BN2V3Ks kJeAf9f24OjzVkhtUgq2BMIay5VRmy7683xncp6XkHkEwIvB/dEq7QDmbv5UVXAa65jMmt/qUn3 rpehEtqY18J/eZmoKe2HmtptdvUb9jrDqVlucdgNkHkHjrdwLhKBg5eL6yZ6BolfB0Kgn/Ln2Hu dd081cxfzwuwOkiozeoDIAB9PV/3hKK2SrCIOXQKWmRPhWfeWWtjOsI1kUoJaKoO6piZjcPfIY3 Z+CewsJQlQEy8ySd1lw== X-Proofpoint-GUID: 5I24hyJiqx5xc0-Em5Rb1QuQEZPb3Z9- X-Proofpoint-ORIG-GUID: 5I24hyJiqx5xc0-Em5Rb1QuQEZPb3Z9- X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-04-02_01,2026-04-01_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 clxscore=1011 adultscore=0 priorityscore=1501 bulkscore=0 phishscore=0 malwarescore=0 lowpriorityscore=0 spamscore=0 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2604020034 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260401_212143_709924_5B93DF1E X-CRM114-Status: GOOD ( 24.47 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: Paolo Bonzini 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. Signed-off-by: Paolo Bonzini Signed-off-by: Steffen Eiden --- arch/x86/kvm/mmu/tdp_mmu.c | 2 +- arch/x86/kvm/vmx/nested.h | 4 ++-- drivers/vfio/vfio_main.c | 10 +--------- include/linux/kvm_host.h | 9 +++++---- include/linux/kvm_types.h | 24 ++++++++++++++++++++++++ virt/kvm/kvm_main.c | 26 +++++--------------------- 6 files changed, 38 insertions(+), 37 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 b1b753889a77..42f515519d87 100644 --- a/drivers/vfio/vfio_main.c +++ b/drivers/vfio/vfio_main.c @@ -437,7 +437,6 @@ 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); @@ -452,14 +451,7 @@ void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm, if (WARN_ON(!pfn)) return; - fn = symbol_get(kvm_get_kvm_safe); - if (WARN_ON(!fn)) { - symbol_put(kvm_put_kvm); - return; - } - - ret = fn(kvm); - symbol_put(kvm_get_kvm_safe); + ret = kvm_get_kvm_safe(kvm); if (!ret) { symbol_put(kvm_put_kvm); return; diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 6b76e7a6f4c2..dc18ee99bba4 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; @@ -876,6 +878,7 @@ struct kvm { #endif char stats_id[KVM_STATS_NAME_SIZE]; }; +static_assert(offsetof(struct kvm, rc) == 0); #define kvm_err(fmt, ...) \ pr_err("kvm [%i]: " fmt, task_pid_nr(current), ## __VA_ARGS__) @@ -1062,8 +1065,6 @@ 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 +1074,7 @@ 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..add7cc2016e8 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 +141,29 @@ 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..cb5e01f92503 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 +1153,7 @@ 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); + 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 +1223,7 @@ 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 +1316,9 @@ 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 +1332,7 @@ 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); -- 2.51.0