1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * kvm asynchronous fault support 4 * 5 * Copyright 2010 Red Hat, Inc. 6 * 7 * Author: 8 * Gleb Natapov <gleb@redhat.com> 9 */ 10 11 #include <linux/kvm_host.h> 12 #include <linux/slab.h> 13 #include <linux/module.h> 14 #include <linux/mmu_context.h> 15 #include <linux/sched/mm.h> 16 17 #include "async_pf.h" 18 #include <trace/events/kvm.h> 19 20 static struct kmem_cache *async_pf_cache; 21 22 int kvm_async_pf_init(void) 23 { 24 async_pf_cache = KMEM_CACHE(kvm_async_pf, 0); 25 26 if (!async_pf_cache) 27 return -ENOMEM; 28 29 return 0; 30 } 31 32 void kvm_async_pf_deinit(void) 33 { 34 kmem_cache_destroy(async_pf_cache); 35 async_pf_cache = NULL; 36 } 37 38 void kvm_async_pf_vcpu_init(struct kvm_vcpu *vcpu) 39 { 40 INIT_LIST_HEAD(&vcpu->async_pf.done); 41 INIT_LIST_HEAD(&vcpu->async_pf.queue); 42 spin_lock_init(&vcpu->async_pf.lock); 43 } 44 45 static void async_pf_execute(struct work_struct *work) 46 { 47 struct kvm_async_pf *apf = 48 container_of(work, struct kvm_async_pf, work); 49 struct kvm_vcpu *vcpu = apf->vcpu; 50 struct mm_struct *mm = vcpu->kvm->mm; 51 unsigned long addr = apf->addr; 52 gpa_t cr2_or_gpa = apf->cr2_or_gpa; 53 int locked = 1; 54 bool first; 55 56 might_sleep(); 57 58 /* 59 * Attempt to pin the VM's host address space, and simply skip gup() if 60 * acquiring a pin fail, i.e. if the process is exiting. Note, KVM 61 * holds a reference to its associated mm_struct until the very end of 62 * kvm_destroy_vm(), i.e. the struct itself won't be freed before this 63 * work item is fully processed. 64 */ 65 if (mmget_not_zero(mm)) { 66 mmap_read_lock(mm); 67 get_user_pages_remote(mm, addr, 1, FOLL_WRITE, NULL, &locked); 68 if (locked) 69 mmap_read_unlock(mm); 70 mmput(mm); 71 } 72 73 /* 74 * Notify and kick the vCPU even if faulting in the page failed, e.g. 75 * so that the vCPU can retry the fault synchronously. 76 */ 77 if (IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC)) 78 kvm_arch_async_page_present(vcpu, apf); 79 80 spin_lock(&vcpu->async_pf.lock); 81 first = list_empty(&vcpu->async_pf.done); 82 list_add_tail(&apf->link, &vcpu->async_pf.done); 83 apf->vcpu = NULL; 84 spin_unlock(&vcpu->async_pf.lock); 85 86 /* 87 * The apf struct may be freed by kvm_check_async_pf_completion() as 88 * soon as the lock is dropped. Nullify it to prevent improper usage. 89 */ 90 apf = NULL; 91 92 if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC) && first) 93 kvm_arch_async_page_present_queued(vcpu); 94 95 trace_kvm_async_pf_completed(addr, cr2_or_gpa); 96 97 __kvm_vcpu_wake_up(vcpu); 98 } 99 100 static void kvm_flush_and_free_async_pf_work(struct kvm_async_pf *work) 101 { 102 /* 103 * The async #PF is "done", but KVM must wait for the work item itself, 104 * i.e. async_pf_execute(), to run to completion. If KVM is a module, 105 * KVM must ensure *no* code owned by the KVM (the module) can be run 106 * after the last call to module_put(). Note, flushing the work item 107 * is always required when the item is taken off the completion queue. 108 * E.g. even if the vCPU handles the item in the "normal" path, the VM 109 * could be terminated before async_pf_execute() completes. 110 * 111 * Wake all events skip the queue and go straight done, i.e. don't 112 * need to be flushed (but sanity check that the work wasn't queued). 113 */ 114 if (work->wakeup_all) 115 WARN_ON_ONCE(work->work.func); 116 else 117 flush_work(&work->work); 118 kmem_cache_free(async_pf_cache, work); 119 } 120 121 void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu) 122 { 123 spin_lock(&vcpu->async_pf.lock); 124 125 /* cancel outstanding work queue item */ 126 while (!list_empty(&vcpu->async_pf.queue)) { 127 struct kvm_async_pf *work = 128 list_first_entry(&vcpu->async_pf.queue, 129 typeof(*work), queue); 130 list_del(&work->queue); 131 132 /* 133 * We know it's present in vcpu->async_pf.done, do 134 * nothing here. 135 */ 136 if (!work->vcpu) 137 continue; 138 139 spin_unlock(&vcpu->async_pf.lock); 140 #ifdef CONFIG_KVM_ASYNC_PF_SYNC 141 flush_work(&work->work); 142 #else 143 if (cancel_work_sync(&work->work)) 144 kmem_cache_free(async_pf_cache, work); 145 #endif 146 spin_lock(&vcpu->async_pf.lock); 147 } 148 149 while (!list_empty(&vcpu->async_pf.done)) { 150 struct kvm_async_pf *work = 151 list_first_entry(&vcpu->async_pf.done, 152 typeof(*work), link); 153 list_del(&work->link); 154 155 spin_unlock(&vcpu->async_pf.lock); 156 kvm_flush_and_free_async_pf_work(work); 157 spin_lock(&vcpu->async_pf.lock); 158 } 159 spin_unlock(&vcpu->async_pf.lock); 160 161 vcpu->async_pf.queued = 0; 162 } 163 164 void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu) 165 { 166 struct kvm_async_pf *work; 167 168 while (!list_empty_careful(&vcpu->async_pf.done) && 169 kvm_arch_can_dequeue_async_page_present(vcpu)) { 170 spin_lock(&vcpu->async_pf.lock); 171 work = list_first_entry(&vcpu->async_pf.done, typeof(*work), 172 link); 173 list_del(&work->link); 174 spin_unlock(&vcpu->async_pf.lock); 175 176 kvm_arch_async_page_ready(vcpu, work); 177 if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC)) 178 kvm_arch_async_page_present(vcpu, work); 179 180 list_del(&work->queue); 181 vcpu->async_pf.queued--; 182 kvm_flush_and_free_async_pf_work(work); 183 } 184 } 185 186 /* 187 * Try to schedule a job to handle page fault asynchronously. Returns 'true' on 188 * success, 'false' on failure (page fault has to be handled synchronously). 189 */ 190 bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, 191 unsigned long hva, struct kvm_arch_async_pf *arch) 192 { 193 struct kvm_async_pf *work; 194 195 if (vcpu->async_pf.queued >= ASYNC_PF_PER_VCPU) 196 return false; 197 198 /* Arch specific code should not do async PF in this case */ 199 if (unlikely(kvm_is_error_hva(hva))) 200 return false; 201 202 /* 203 * do alloc nowait since if we are going to sleep anyway we 204 * may as well sleep faulting in page 205 */ 206 work = kmem_cache_zalloc(async_pf_cache, GFP_NOWAIT | __GFP_NOWARN); 207 if (!work) 208 return false; 209 210 work->wakeup_all = false; 211 work->vcpu = vcpu; 212 work->cr2_or_gpa = cr2_or_gpa; 213 work->addr = hva; 214 work->arch = *arch; 215 216 INIT_WORK(&work->work, async_pf_execute); 217 218 list_add_tail(&work->queue, &vcpu->async_pf.queue); 219 vcpu->async_pf.queued++; 220 work->notpresent_injected = kvm_arch_async_page_not_present(vcpu, work); 221 222 schedule_work(&work->work); 223 224 return true; 225 } 226 227 int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu) 228 { 229 struct kvm_async_pf *work; 230 bool first; 231 232 if (!list_empty_careful(&vcpu->async_pf.done)) 233 return 0; 234 235 work = kmem_cache_zalloc(async_pf_cache, GFP_ATOMIC); 236 if (!work) 237 return -ENOMEM; 238 239 work->wakeup_all = true; 240 INIT_LIST_HEAD(&work->queue); /* for list_del to work */ 241 242 spin_lock(&vcpu->async_pf.lock); 243 first = list_empty(&vcpu->async_pf.done); 244 list_add_tail(&work->link, &vcpu->async_pf.done); 245 spin_unlock(&vcpu->async_pf.lock); 246 247 if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC) && first) 248 kvm_arch_async_page_present_queued(vcpu); 249 250 vcpu->async_pf.queued++; 251 return 0; 252 } 253