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 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         spin_unlock(&vcpu->async_pf.lock);
  84
  85         /*
  86          * The apf struct may be freed by kvm_check_async_pf_completion() as
  87          * soon as the lock is dropped.  Nullify it to prevent improper usage.
  88          */
  89         apf = NULL;
  90
  91         if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC) && first)
  92                 kvm_arch_async_page_present_queued(vcpu);
  93
  94         trace_kvm_async_pf_completed(addr, cr2_or_gpa);
  95
  96         __kvm_vcpu_wake_up(vcpu);
  97 }
  98
  99 static void kvm_flush_and_free_async_pf_work(struct kvm_async_pf *work)
 100 {
 101         /*
 102          * The async #PF is "done", but KVM must wait for the work item itself,
 103          * i.e. async_pf_execute(), to run to completion.  If KVM is a module,
 104          * KVM must ensure *no* code owned by the KVM (the module) can be run
 105          * after the last call to module_put().  Note, flushing the work item
 106          * is always required when the item is taken off the completion queue.
 107          * E.g. even if the vCPU handles the item in the "normal" path, the VM
 108          * could be terminated before async_pf_execute() completes.
 109          *
 110          * Wake all events skip the queue and go straight done, i.e. don't
 111          * need to be flushed (but sanity check that the work wasn't queued).
 112          */
 113         if (work->wakeup_all)
 114                 WARN_ON_ONCE(work->work.func);
 115         else
 116                 flush_work(&work->work);
 117         kmem_cache_free(async_pf_cache, work);
 118 }
 119
 120 void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu)
 121 {
 122         /* cancel outstanding work queue item */
 123         while (!list_empty(&vcpu->async_pf.queue)) {
 124                 struct kvm_async_pf *work =
 125                         list_first_entry(&vcpu->async_pf.queue,
 126                                          typeof(*work), queue);
 127                 list_del(&work->queue);
 128
 129 #ifdef CONFIG_KVM_ASYNC_PF_SYNC
 130                 flush_work(&work->work);
 131 #else
 132                 if (cancel_work_sync(&work->work))
 133                         kmem_cache_free(async_pf_cache, work);
 134 #endif
 135         }
 136
 137         spin_lock(&vcpu->async_pf.lock);
 138         while (!list_empty(&vcpu->async_pf.done)) {
 139                 struct kvm_async_pf *work =
 140                         list_first_entry(&vcpu->async_pf.done,
 141                                          typeof(*work), link);
 142                 list_del(&work->link);
 143
 144                 spin_unlock(&vcpu->async_pf.lock);
 145                 kvm_flush_and_free_async_pf_work(work);
 146                 spin_lock(&vcpu->async_pf.lock);
 147         }
 148         spin_unlock(&vcpu->async_pf.lock);
 149
 150         vcpu->async_pf.queued = 0;
 151 }
 152
 153 void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu)
 154 {
 155         struct kvm_async_pf *work;
 156
 157         while (!list_empty_careful(&vcpu->async_pf.done) &&
 158               kvm_arch_can_dequeue_async_page_present(vcpu)) {
 159                 spin_lock(&vcpu->async_pf.lock);
 160                 work = list_first_entry(&vcpu->async_pf.done, typeof(*work),
 161                                               link);
 162                 list_del(&work->link);
 163                 spin_unlock(&vcpu->async_pf.lock);
 164
 165                 kvm_arch_async_page_ready(vcpu, work);
 166                 if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC))
 167                         kvm_arch_async_page_present(vcpu, work);
 168
 169                 list_del(&work->queue);
 170                 vcpu->async_pf.queued--;
 171                 kvm_flush_and_free_async_pf_work(work);
 172         }
 173 }
 174
 175 /*
 176  * Try to schedule a job to handle page fault asynchronously. Returns 'true' on
 177  * success, 'false' on failure (page fault has to be handled synchronously).
 178  */
 179 bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 180                         unsigned long hva, struct kvm_arch_async_pf *arch)
 181 {
 182         struct kvm_async_pf *work;
 183
 184         if (vcpu->async_pf.queued >= ASYNC_PF_PER_VCPU)
 185                 return false;
 186
 187         /* Arch specific code should not do async PF in this case */
 188         if (unlikely(kvm_is_error_hva(hva)))
 189                 return false;
 190
 191         /*
 192          * do alloc nowait since if we are going to sleep anyway we
 193          * may as well sleep faulting in page
 194          */
 195         work = kmem_cache_zalloc(async_pf_cache, GFP_NOWAIT | __GFP_NOWARN);
 196         if (!work)
 197                 return false;
 198
 199         work->wakeup_all = false;
 200         work->vcpu = vcpu;
 201         work->cr2_or_gpa = cr2_or_gpa;
 202         work->addr = hva;
 203         work->arch = *arch;
 204
 205         INIT_WORK(&work->work, async_pf_execute);
 206
 207         list_add_tail(&work->queue, &vcpu->async_pf.queue);
 208         vcpu->async_pf.queued++;
 209         work->notpresent_injected = kvm_arch_async_page_not_present(vcpu, work);
 210
 211         schedule_work(&work->work);
 212
 213         return true;
 214 }
 215
 216 int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu)
 217 {
 218         struct kvm_async_pf *work;
 219         bool first;
 220
 221         if (!list_empty_careful(&vcpu->async_pf.done))
 222                 return 0;
 223
 224         work = kmem_cache_zalloc(async_pf_cache, GFP_ATOMIC);
 225         if (!work)
 226                 return -ENOMEM;
 227
 228         work->wakeup_all = true;
 229         INIT_LIST_HEAD(&work->queue); /* for list_del to work */
 230
 231         spin_lock(&vcpu->async_pf.lock);
 232         first = list_empty(&vcpu->async_pf.done);
 233         list_add_tail(&work->link, &vcpu->async_pf.done);
 234         spin_unlock(&vcpu->async_pf.lock);
 235
 236         if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC) && first)
 237                 kvm_arch_async_page_present_queued(vcpu);
 238
 239         vcpu->async_pf.queued++;
 240         return 0;
 241 }