KVM: Halt vcpu if page it tries to access is swapped out

If a guest accesses swapped out memory do not swap it in from vcpu thread
context. Schedule work to do swapping and put vcpu into halted state
instead.

Interrupts will still be delivered to the guest and if interrupt will
cause reschedule guest will continue to run another task.

[avi: remove call to get_user_pages_noio(), nacked by Linus; this
      makes everything synchrnous again]

Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 190 insertions, 0 deletions

diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
new file mode 100644
index 0000000..857d634
--- /dev/null
+++ b/virt/kvm/async_pf.c
@@ -0,0 +1,190 @@
+/*
+ * kvm asynchronous fault support
+ *
+ * Copyright 2010 Red Hat, Inc.
+ *
+ * Author:
+ *      Gleb Natapov <gleb@redhat.com>
+ *
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#include <linux/kvm_host.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/mmu_context.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)
+{
+	if (async_pf_cache)
+		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 page *page = NULL;
+	struct kvm_async_pf *apf =
+		container_of(work, struct kvm_async_pf, work);
+	struct mm_struct *mm = apf->mm;
+	struct kvm_vcpu *vcpu = apf->vcpu;
+	unsigned long addr = apf->addr;
+	gva_t gva = apf->gva;
+
+	might_sleep();
+
+	use_mm(mm);
+	down_read(&mm->mmap_sem);
+	get_user_pages(current, mm, addr, 1, 1, 0, &page, NULL);
+	up_read(&mm->mmap_sem);
+	unuse_mm(mm);
+
+	spin_lock(&vcpu->async_pf.lock);
+	list_add_tail(&apf->link, &vcpu->async_pf.done);
+	apf->page = page;
+	apf->done = true;
+	spin_unlock(&vcpu->async_pf.lock);
+
+	/*
+	 * apf may be freed by kvm_check_async_pf_completion() after
+	 * this point
+	 */
+
+	trace_kvm_async_pf_completed(addr, page, gva);
+
+	if (waitqueue_active(&vcpu->wq))
+		wake_up_interruptible(&vcpu->wq);
+
+	mmdrop(mm);
+	kvm_put_kvm(vcpu->kvm);
+}
+
+void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu)
+{
+	/* cancel outstanding work queue item */
+	while (!list_empty(&vcpu->async_pf.queue)) {
+		struct kvm_async_pf *work =
+			list_entry(vcpu->async_pf.queue.next,
+				   typeof(*work), queue);
+		cancel_work_sync(&work->work);
+		list_del(&work->queue);
+		if (!work->done) /* work was canceled */
+			kmem_cache_free(async_pf_cache, work);
+	}
+
+	spin_lock(&vcpu->async_pf.lock);
+	while (!list_empty(&vcpu->async_pf.done)) {
+		struct kvm_async_pf *work =
+			list_entry(vcpu->async_pf.done.next,
+				   typeof(*work), link);
+		list_del(&work->link);
+		if (work->page)
+			put_page(work->page);
+		kmem_cache_free(async_pf_cache, work);
+	}
+	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;
+
+	if (list_empty_careful(&vcpu->async_pf.done))
+		return;
+
+	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_present(vcpu, work);
+
+	list_del(&work->queue);
+	vcpu->async_pf.queued--;
+	if (work->page)
+		put_page(work->page);
+	kmem_cache_free(async_pf_cache, work);
+}
+
+int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn,
+		       struct kvm_arch_async_pf *arch)
+{
+	struct kvm_async_pf *work;
+
+	if (vcpu->async_pf.queued >= ASYNC_PF_PER_VCPU)
+		return 0;
+
+	/* setup delayed work */
+
+	/*
+	 * 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);
+	if (!work)
+		return 0;
+
+	work->page = NULL;
+	work->done = false;
+	work->vcpu = vcpu;
+	work->gva = gva;
+	work->addr = gfn_to_hva(vcpu->kvm, gfn);
+	work->arch = *arch;
+	work->mm = current->mm;
+	atomic_inc(&work->mm->mm_count);
+	kvm_get_kvm(work->vcpu->kvm);
+
+	/* this can't really happen otherwise gfn_to_pfn_async
+	   would succeed */
+	if (unlikely(kvm_is_error_hva(work->addr)))
+		goto retry_sync;
+
+	INIT_WORK(&work->work, async_pf_execute);
+	if (!schedule_work(&work->work))
+		goto retry_sync;
+
+	list_add_tail(&work->queue, &vcpu->async_pf.queue);
+	vcpu->async_pf.queued++;
+	kvm_arch_async_page_not_present(vcpu, work);
+	return 1;
+retry_sync:
+	kvm_put_kvm(work->vcpu->kvm);
+	mmdrop(work->mm);
+	kmem_cache_free(async_pf_cache, work);
+	return 0;
+}