diff options
| -rw-r--r-- | Documentation/virt/kvm/locking.rst | 9 | ||||
| -rw-r--r-- | virt/kvm/kvm_main.c | 174 |
2 files changed, 66 insertions, 117 deletions
diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst index c0cb5ce51c1e..be3c323888b1 100644 --- a/Documentation/virt/kvm/locking.rst +++ b/Documentation/virt/kvm/locking.rst @@ -9,7 +9,9 @@ KVM Lock Overview The acquisition orders for mutexes are as follows: -- cpus_read_lock() is taken outside kvm_lock and kvm_usage_lock +- cpus_read_lock() is taken outside kvm_lock + +- kvm_usage_lock is taken outside cpus_read_lock() - kvm->lock is taken outside vcpu->mutex @@ -241,9 +243,8 @@ time it will be set using the Dirty tracking mechanism described above. :Arch: any :Protects: - kvm_usage_count - hardware virtualization enable/disable -:Comment: Exists because using kvm_lock leads to deadlock (see earlier comment - on cpus_read_lock() vs kvm_lock). Note, KVM also disables CPU hotplug via - cpus_read_lock() when enabling/disabling virtualization. +:Comment: Exists to allow taking cpus_read_lock() while kvm_usage_count is + protected, which simplifies the virtualization enabling logic. ``kvm->mn_invalidate_lock`` ^^^^^^^^^^^^^^^^^^^^^^^^^^^ diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 7164a9ece208..9ad8903b575a 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -5578,7 +5578,7 @@ static DEFINE_PER_CPU(bool, hardware_enabled); static DEFINE_MUTEX(kvm_usage_lock); static int kvm_usage_count; -static int __hardware_enable_nolock(void) +static int hardware_enable_nolock(void) { if (__this_cpu_read(hardware_enabled)) return 0; @@ -5593,34 +5593,18 @@ static int __hardware_enable_nolock(void) return 0; } -static void hardware_enable_nolock(void *failed) -{ - if (__hardware_enable_nolock()) - atomic_inc(failed); -} - static int kvm_online_cpu(unsigned int cpu) { - int ret = 0; - /* * Abort the CPU online process if hardware virtualization cannot * be enabled. Otherwise running VMs would encounter unrecoverable * errors when scheduled to this CPU. */ - mutex_lock(&kvm_usage_lock); - if (kvm_usage_count) - ret = __hardware_enable_nolock(); - mutex_unlock(&kvm_usage_lock); - return ret; + return hardware_enable_nolock(); } static void hardware_disable_nolock(void *junk) { - /* - * Note, hardware_disable_all_nolock() tells all online CPUs to disable - * hardware, not just CPUs that successfully enabled hardware! - */ if (!__this_cpu_read(hardware_enabled)) return; @@ -5631,78 +5615,10 @@ static void hardware_disable_nolock(void *junk) static int kvm_offline_cpu(unsigned int cpu) { - mutex_lock(&kvm_usage_lock); - if (kvm_usage_count) - hardware_disable_nolock(NULL); - mutex_unlock(&kvm_usage_lock); + hardware_disable_nolock(NULL); return 0; } -static void hardware_disable_all_nolock(void) -{ - BUG_ON(!kvm_usage_count); - - kvm_usage_count--; - if (!kvm_usage_count) - on_each_cpu(hardware_disable_nolock, NULL, 1); -} - -static void hardware_disable_all(void) -{ - cpus_read_lock(); - mutex_lock(&kvm_usage_lock); - hardware_disable_all_nolock(); - mutex_unlock(&kvm_usage_lock); - cpus_read_unlock(); -} - -static int hardware_enable_all(void) -{ - atomic_t failed = ATOMIC_INIT(0); - int r; - - /* - * Do not enable hardware virtualization if the system is going down. - * If userspace initiated a forced reboot, e.g. reboot -f, then it's - * possible for an in-flight KVM_CREATE_VM to trigger hardware enabling - * after kvm_reboot() is called. Note, this relies on system_state - * being set _before_ kvm_reboot(), which is why KVM uses a syscore ops - * hook instead of registering a dedicated reboot notifier (the latter - * runs before system_state is updated). - */ - if (system_state == SYSTEM_HALT || system_state == SYSTEM_POWER_OFF || - system_state == SYSTEM_RESTART) - return -EBUSY; - - /* - * When onlining a CPU, cpu_online_mask is set before kvm_online_cpu() - * is called, and so on_each_cpu() between them includes the CPU that - * is being onlined. As a result, hardware_enable_nolock() may get - * invoked before kvm_online_cpu(), which also enables hardware if the - * usage count is non-zero. Disable CPU hotplug to avoid attempting to - * enable hardware multiple times. - */ - cpus_read_lock(); - mutex_lock(&kvm_usage_lock); - - r = 0; - - kvm_usage_count++; - if (kvm_usage_count == 1) { - on_each_cpu(hardware_enable_nolock, &failed, 1); - - if (atomic_read(&failed)) { - hardware_disable_all_nolock(); - r = -EBUSY; - } - } - - mutex_unlock(&kvm_usage_lock); - cpus_read_unlock(); - - return r; -} - static void kvm_shutdown(void) { /* @@ -5734,8 +5650,7 @@ static int kvm_suspend(void) lockdep_assert_not_held(&kvm_usage_lock); lockdep_assert_irqs_disabled(); - if (kvm_usage_count) - hardware_disable_nolock(NULL); + hardware_disable_nolock(NULL); return 0; } @@ -5744,8 +5659,7 @@ static void kvm_resume(void) lockdep_assert_not_held(&kvm_usage_lock); lockdep_assert_irqs_disabled(); - if (kvm_usage_count) - WARN_ON_ONCE(__hardware_enable_nolock()); + WARN_ON_ONCE(hardware_enable_nolock()); } static struct syscore_ops kvm_syscore_ops = { @@ -5753,6 +5667,60 @@ static struct syscore_ops kvm_syscore_ops = { .resume = kvm_resume, .shutdown = kvm_shutdown, }; + +static int hardware_enable_all(void) +{ + int r; + + guard(mutex)(&kvm_usage_lock); + + if (kvm_usage_count++) + return 0; + + r = cpuhp_setup_state(CPUHP_AP_KVM_ONLINE, "kvm/cpu:online", + kvm_online_cpu, kvm_offline_cpu); + if (r) + goto err_cpuhp; + + register_syscore_ops(&kvm_syscore_ops); + + /* + * Undo virtualization enabling and bail if the system is going down. + * If userspace initiated a forced reboot, e.g. reboot -f, then it's + * possible for an in-flight operation to enable virtualization after + * syscore_shutdown() is called, i.e. without kvm_shutdown() being + * invoked. Note, this relies on system_state being set _before_ + * kvm_shutdown(), e.g. to ensure either kvm_shutdown() is invoked + * or this CPU observes the impending shutdown. Which is why KVM uses + * a syscore ops hook instead of registering a dedicated reboot + * notifier (the latter runs before system_state is updated). + */ + if (system_state == SYSTEM_HALT || system_state == SYSTEM_POWER_OFF || + system_state == SYSTEM_RESTART) { + r = -EBUSY; + goto err_rebooting; + } + + return 0; + +err_rebooting: + unregister_syscore_ops(&kvm_syscore_ops); + cpuhp_remove_state(CPUHP_AP_KVM_ONLINE); +err_cpuhp: + --kvm_usage_count; + return r; +} + +static void hardware_disable_all(void) +{ + guard(mutex)(&kvm_usage_lock); + + if (--kvm_usage_count) + return; + + unregister_syscore_ops(&kvm_syscore_ops); + cpuhp_remove_state(CPUHP_AP_KVM_ONLINE); +} #else /* CONFIG_KVM_GENERIC_HARDWARE_ENABLING */ static int hardware_enable_all(void) { @@ -6461,15 +6429,6 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module) int r; int cpu; -#ifdef CONFIG_KVM_GENERIC_HARDWARE_ENABLING - r = cpuhp_setup_state_nocalls(CPUHP_AP_KVM_ONLINE, "kvm/cpu:online", - kvm_online_cpu, kvm_offline_cpu); - if (r) - return r; - - register_syscore_ops(&kvm_syscore_ops); -#endif - /* A kmem cache lets us meet the alignment requirements of fx_save. */ if (!vcpu_align) vcpu_align = __alignof__(struct kvm_vcpu); @@ -6480,10 +6439,8 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module) offsetofend(struct kvm_vcpu, stats_id) - offsetof(struct kvm_vcpu, arch), NULL); - if (!kvm_vcpu_cache) { - r = -ENOMEM; - goto err_vcpu_cache; - } + if (!kvm_vcpu_cache) + return -ENOMEM; for_each_possible_cpu(cpu) { if (!alloc_cpumask_var_node(&per_cpu(cpu_kick_mask, cpu), @@ -6540,11 +6497,6 @@ err_cpu_kick_mask: for_each_possible_cpu(cpu) free_cpumask_var(per_cpu(cpu_kick_mask, cpu)); kmem_cache_destroy(kvm_vcpu_cache); -err_vcpu_cache: -#ifdef CONFIG_KVM_GENERIC_HARDWARE_ENABLING - unregister_syscore_ops(&kvm_syscore_ops); - cpuhp_remove_state_nocalls(CPUHP_AP_KVM_ONLINE); -#endif return r; } EXPORT_SYMBOL_GPL(kvm_init); @@ -6566,10 +6518,6 @@ void kvm_exit(void) kmem_cache_destroy(kvm_vcpu_cache); kvm_vfio_ops_exit(); kvm_async_pf_deinit(); -#ifdef CONFIG_KVM_GENERIC_HARDWARE_ENABLING - unregister_syscore_ops(&kvm_syscore_ops); - cpuhp_remove_state_nocalls(CPUHP_AP_KVM_ONLINE); -#endif kvm_irqfd_exit(); } EXPORT_SYMBOL_GPL(kvm_exit); |