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