virt/kvm/async_pf.c
// SPDX-License-Identifier: GPL-2.0-only
/*
* kvm asynchronous fault support
*
* Copyright 2010 Red Hat, Inc.
*
* Author:
* Gleb Natapov <gleb@redhat.com>
*/
#include <linux/kvm_host.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/mmu_context.h>
#include <linux/sched/mm.h>
#include "async_pf.h"
#include <trace/events/kvm.h>
static struct kmem_cache *async_pf_cache;
int kvm_async_pf_init(void)
{
async_pf_cache = KMEM_CACHE(kvm_async_pf, 0);
if (!async_pf_cache)
return -ENOMEM;
return 0;
}
void kvm_async_pf_deinit(void)
{
kmem_cache_destroy(async_pf_cache);
async_pf_cache = NULL;
}
void kvm_async_pf_vcpu_init(struct kvm_vcpu *vcpu)
{
INIT_LIST_HEAD(&vcpu->async_pf.done);
INIT_LIST_HEAD(&vcpu->async_pf.queue);
spin_lock_init(&vcpu->async_pf.lock);
}
static void async_pf_execute(struct work_struct *work)
{
struct kvm_async_pf *apf =
container_of(work, struct kvm_async_pf, work);
struct kvm_vcpu *vcpu = apf->vcpu;
struct mm_struct *mm = vcpu->kvm->mm;
unsigned long addr = apf->addr;
gpa_t cr2_or_gpa = apf->cr2_or_gpa;
int locked = 1;
bool first;
might_sleep();
/*
* Attempt to pin the VM's host address space, and simply skip gup() if
* acquiring a pin fail, i.e. if the process is exiting. Note, KVM
* holds a reference to its associated mm_struct until the very end of
* kvm_destroy_vm(), i.e. the struct itself won't be freed before this
* work item is fully processed.
*/
if (mmget_not_zero(mm)) {
mmap_read_lock(mm);
get_user_pages_remote(mm, addr, 1, FOLL_WRITE, NULL, &locked);
if (locked)
mmap_read_unlock(mm);
mmput(mm);
}
/*
* Notify and kick the vCPU even if faulting in the page failed, e.g.
* so that the vCPU can retry the fault synchronously.
*/
if (IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC))
kvm_arch_async_page_present(vcpu, apf);
spin_lock(&vcpu->async_pf.lock);
first = list_empty(&vcpu->async_pf.done);
list_add_tail(&apf->link, &vcpu->async_pf.done);
apf->vcpu = NULL;
spin_unlock(&vcpu->async_pf.lock);
/*
* The apf struct may be freed by kvm_check_async_pf_completion() as
* soon as the lock is dropped. Nullify it to prevent improper usage.
*/
apf = NULL;
if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC) && first)
kvm_arch_async_page_present_queued(vcpu);
trace_kvm_async_pf_completed(addr, cr2_or_gpa);
__kvm_vcpu_wake_up(vcpu);
}
static void kvm_flush_and_free_async_pf_work(struct kvm_async_pf *work)
{
/*
* The async #PF is "done", but KVM must wait for the work item itself,
* i.e. async_pf_execute(), to run to completion. If KVM is a module,
* KVM must ensure *no* code owned by the KVM (the module) can be run
* after the last call to module_put(). Note, flushing the work item
* is always required when the item is taken off the completion queue.
* E.g. even if the vCPU handles the item in the "normal" path, the VM
* could be terminated before async_pf_execute() completes.
*
* Wake all events skip the queue and go straight done, i.e. don't
* need to be flushed (but sanity check that the work wasn't queued).
*/
if (work->wakeup_all)
WARN_ON_ONCE(work->work.func);
else
flush_work(&work->work);
kmem_cache_free(async_pf_cache, work);
}
void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu)
{
spin_lock(&vcpu->async_pf.lock);
/* cancel outstanding work queue item */
while (!list_empty(&vcpu->async_pf.queue)) {
struct kvm_async_pf *work =
list_first_entry(&vcpu->async_pf.queue,
typeof(*work), queue);
list_del(&work->queue);
/*
* We know it's present in vcpu->async_pf.done, do
* nothing here.
*/
if (!work->vcpu)
continue;
spin_unlock(&vcpu->async_pf.lock);
#ifdef CONFIG_KVM_ASYNC_PF_SYNC
flush_work(&work->work);
#else
if (cancel_work_sync(&work->work))
kmem_cache_free(async_pf_cache, work);
#endif
spin_lock(&vcpu->async_pf.lock);
}
while (!list_empty(&vcpu->async_pf.done)) {
struct kvm_async_pf *work =
list_first_entry(&vcpu->async_pf.done,
typeof(*work), link);
list_del(&work->link);
spin_unlock(&vcpu->async_pf.lock);
kvm_flush_and_free_async_pf_work(work);
spin_lock(&vcpu->async_pf.lock);
}
spin_unlock(&vcpu->async_pf.lock);
vcpu->async_pf.queued = 0;
}
void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu)
{
struct kvm_async_pf *work;
while (!list_empty_careful(&vcpu->async_pf.done) &&
kvm_arch_can_dequeue_async_page_present(vcpu)) {
spin_lock(&vcpu->async_pf.lock);
work = list_first_entry(&vcpu->async_pf.done, typeof(*work),
link);
list_del(&work->link);
spin_unlock(&vcpu->async_pf.lock);
kvm_arch_async_page_ready(vcpu, work);
if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC))
kvm_arch_async_page_present(vcpu, work);
list_del(&work->queue);
vcpu->async_pf.queued--;
kvm_flush_and_free_async_pf_work(work);
}
}
/*
* Try to schedule a job to handle page fault asynchronously. Returns 'true' on
* success, 'false' on failure (page fault has to be handled synchronously).
*/
bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
unsigned long hva, struct kvm_arch_async_pf *arch)
{
struct kvm_async_pf *work;
if (vcpu->async_pf.queued >= ASYNC_PF_PER_VCPU)
return false;
/* Arch specific code should not do async PF in this case */
if (unlikely(kvm_is_error_hva(hva)))
return false;
/*
* do alloc nowait since if we are going to sleep anyway we
* may as well sleep faulting in page
*/
work = kmem_cache_zalloc(async_pf_cache, GFP_NOWAIT | __GFP_NOWARN);
if (!work)
return false;
work->wakeup_all = false;
work->vcpu = vcpu;
work->cr2_or_gpa = cr2_or_gpa;
work->addr = hva;
work->arch = *arch;
INIT_WORK(&work->work, async_pf_execute);
list_add_tail(&work->queue, &vcpu->async_pf.queue);
vcpu->async_pf.queued++;
work->notpresent_injected = kvm_arch_async_page_not_present(vcpu, work);
schedule_work(&work->work);
return true;
}
int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu)
{
struct kvm_async_pf *work;
bool first;
if (!list_empty_careful(&vcpu->async_pf.done))
return 0;
work = kmem_cache_zalloc(async_pf_cache, GFP_ATOMIC);
if (!work)
return -ENOMEM;
work->wakeup_all = true;
INIT_LIST_HEAD(&work->queue); /* for list_del to work */
spin_lock(&vcpu->async_pf.lock);
first = list_empty(&vcpu->async_pf.done);
list_add_tail(&work->link, &vcpu->async_pf.done);
spin_unlock(&vcpu->async_pf.lock);
if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC) && first)
kvm_arch_async_page_present_queued(vcpu);
vcpu->async_pf.queued++;
return 0;
}