virt/kvm/async_pf.c

   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 mm_struct *mm = apf->mm;
  50         struct kvm_vcpu *vcpu = apf->vcpu;
  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          * This work is run asynchronously to the task which owns
  60          * mm and might be done in another context, so we must
  61          * access remotely.
  62          */
  63         mmap_read_lock(mm);
  64         get_user_pages_remote(mm, addr, 1, FOLL_WRITE, NULL, NULL,
  65                         &locked);
  66         if (locked)
  67                 mmap_read_unlock(mm);
  68
  69         if (IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC))
  70                 kvm_arch_async_page_present(vcpu, apf);
  71
  72         spin_lock(&vcpu->async_pf.lock);
  73         first = list_empty(&vcpu->async_pf.done);
  74         list_add_tail(&apf->link, &vcpu->async_pf.done);
  75         apf->vcpu = NULL;
  76         spin_unlock(&vcpu->async_pf.lock);
  77
  78         if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC) && first)
  79                 kvm_arch_async_page_present_queued(vcpu);
  80
  81         /*
  82          * apf may be freed by kvm_check_async_pf_completion() after
  83          * this point
  84          */
  85
  86         trace_kvm_async_pf_completed(addr, cr2_or_gpa);
  87
  88         __kvm_vcpu_wake_up(vcpu);
  89
  90         mmput(mm);
  91 }
  92
  93 static void kvm_flush_and_free_async_pf_work(struct kvm_async_pf *work)
  94 {
  95         /*
  96          * The async #PF is "done", but KVM must wait for the work item itself,
  97          * i.e. async_pf_execute(), to run to completion.  If KVM is a module,
  98          * KVM must ensure *no* code owned by the KVM (the module) can be run
  99          * after the last call to module_put().  Note, flushing the work item
 100          * is always required when the item is taken off the completion queue.
 101          * E.g. even if the vCPU handles the item in the "normal" path, the VM
 102          * could be terminated before async_pf_execute() completes.
 103          *
 104          * Wake all events skip the queue and go straight done, i.e. don't
 105          * need to be flushed (but sanity check that the work wasn't queued).
 106          */
 107         if (work->wakeup_all)
 108                 WARN_ON_ONCE(work->work.func);
 109         else
 110                 flush_work(&work->work);
 111         kmem_cache_free(async_pf_cache, work);
 112 }
 113
 114 void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu)
 115 {
 116         spin_lock(&vcpu->async_pf.lock);
 117
 118         /* cancel outstanding work queue item */
 119         while (!list_empty(&vcpu->async_pf.queue)) {
 120                 struct kvm_async_pf *work =
 121                         list_first_entry(&vcpu->async_pf.queue,
 122                                          typeof(*work), queue);
 123                 list_del(&work->queue);
 124
 125                 /*
 126                  * We know it's present in vcpu->async_pf.done, do
 127                  * nothing here.
 128                  */
 129                 if (!work->vcpu)
 130                         continue;
 131
 132                 spin_unlock(&vcpu->async_pf.lock);
 133 #ifdef CONFIG_KVM_ASYNC_PF_SYNC
 134                 flush_work(&work->work);
 135 #else
 136                 if (cancel_work_sync(&work->work)) {
 137                         mmput(work->mm);
 138                         kmem_cache_free(async_pf_cache, work);
 139                 }
 140 #endif
 141                 spin_lock(&vcpu->async_pf.lock);
 142         }
 143
 144         while (!list_empty(&vcpu->async_pf.done)) {
 145                 struct kvm_async_pf *work =
 146                         list_first_entry(&vcpu->async_pf.done,
 147                                          typeof(*work), link);
 148                 list_del(&work->link);
 149
 150                 spin_unlock(&vcpu->async_pf.lock);
 151                 kvm_flush_and_free_async_pf_work(work);
 152                 spin_lock(&vcpu->async_pf.lock);
 153         }
 154         spin_unlock(&vcpu->async_pf.lock);
 155
 156         vcpu->async_pf.queued = 0;
 157 }
 158
 159 void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu)
 160 {
 161         struct kvm_async_pf *work;
 162
 163         while (!list_empty_careful(&vcpu->async_pf.done) &&
 164               kvm_arch_can_dequeue_async_page_present(vcpu)) {
 165                 spin_lock(&vcpu->async_pf.lock);
 166                 work = list_first_entry(&vcpu->async_pf.done, typeof(*work),
 167                                               link);
 168                 list_del(&work->link);
 169                 spin_unlock(&vcpu->async_pf.lock);
 170
 171                 kvm_arch_async_page_ready(vcpu, work);
 172                 if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC))
 173                         kvm_arch_async_page_present(vcpu, work);
 174
 175                 list_del(&work->queue);
 176                 vcpu->async_pf.queued--;
 177                 kvm_flush_and_free_async_pf_work(work);
 178         }
 179 }
 180
 181 /*
 182  * Try to schedule a job to handle page fault asynchronously. Returns 'true' on
 183  * success, 'false' on failure (page fault has to be handled synchronously).
 184  */
 185 bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 186                         unsigned long hva, struct kvm_arch_async_pf *arch)
 187 {
 188         struct kvm_async_pf *work;
 189
 190         if (vcpu->async_pf.queued >= ASYNC_PF_PER_VCPU)
 191                 return false;
 192
 193         /* Arch specific code should not do async PF in this case */
 194         if (unlikely(kvm_is_error_hva(hva)))
 195                 return false;
 196
 197         /*
 198          * do alloc nowait since if we are going to sleep anyway we
 199          * may as well sleep faulting in page
 200          */
 201         work = kmem_cache_zalloc(async_pf_cache, GFP_NOWAIT | __GFP_NOWARN);
 202         if (!work)
 203                 return false;
 204
 205         work->wakeup_all = false;
 206         work->vcpu = vcpu;
 207         work->cr2_or_gpa = cr2_or_gpa;
 208         work->addr = hva;
 209         work->arch = *arch;
 210         work->mm = current->mm;
 211         mmget(work->mm);
 212
 213         INIT_WORK(&work->work, async_pf_execute);
 214
 215         list_add_tail(&work->queue, &vcpu->async_pf.queue);
 216         vcpu->async_pf.queued++;
 217         work->notpresent_injected = kvm_arch_async_page_not_present(vcpu, work);
 218
 219         schedule_work(&work->work);
 220
 221         return true;
 222 }
 223
 224 int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu)
 225 {
 226         struct kvm_async_pf *work;
 227         bool first;
 228
 229         if (!list_empty_careful(&vcpu->async_pf.done))
 230                 return 0;
 231
 232         work = kmem_cache_zalloc(async_pf_cache, GFP_ATOMIC);
 233         if (!work)
 234                 return -ENOMEM;
 235
 236         work->wakeup_all = true;
 237         INIT_LIST_HEAD(&work->queue); /* for list_del to work */
 238
 239         spin_lock(&vcpu->async_pf.lock);
 240         first = list_empty(&vcpu->async_pf.done);
 241         list_add_tail(&work->link, &vcpu->async_pf.done);
 242         spin_unlock(&vcpu->async_pf.lock);
 243
 244         if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC) && first)
 245                 kvm_arch_async_page_present_queued(vcpu);
 246
 247         vcpu->async_pf.queued++;
 248         return 0;
 249 }