KVM: async_pf: mm->mm_users can not pin apf->mm

commit 41c22f626254b9dc0376928cae009e73d1b6a49a upstream.

get_user_pages(mm) is simply wrong if mm->mm_users == 0 and exit_mmap/etc
was already called (or is in progress), mm->mm_count can only pin mm->pgd
and mm_struct itself.

Change kvm_setup_async_pf/async_pf_execute to inc/dec mm->mm_users.

kvm_create_vm/kvm_destroy_vm play with ->mm_count too but this case looks
fine at first glance, it seems that this ->mm is only used to verify that
current->mm == kvm->mm.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 8631d9c..f2c80d5 100644 (file)
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -85,7 +85,7 @@ static void async_pf_execute(struct work_struct *work)
        if (waitqueue_active(&vcpu->wq))
                wake_up_interruptible(&vcpu->wq);
 
-       mmdrop(mm);
+       mmput(mm);
        kvm_put_kvm(vcpu->kvm);
 }
 
@@ -98,7 +98,7 @@ void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu)
                                   typeof(*work), queue);
                list_del(&work->queue);
                if (cancel_work_sync(&work->work)) {
-                       mmdrop(work->mm);
+                       mmput(work->mm);
                        kvm_put_kvm(vcpu->kvm); /* == work->vcpu->kvm */
                        kmem_cache_free(async_pf_cache, work);
                }
@@ -162,7 +162,7 @@ int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn,
        work->addr = gfn_to_hva(vcpu->kvm, gfn);
        work->arch = *arch;
        work->mm = current->mm;
-       atomic_inc(&work->mm->mm_count);
+       atomic_inc(&work->mm->mm_users);
        kvm_get_kvm(work->vcpu->kvm);
 
        /* this can't really happen otherwise gfn_to_pfn_async
@@ -180,7 +180,7 @@ int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn,
        return 1;
 retry_sync:
        kvm_put_kvm(work->vcpu->kvm);
-       mmdrop(work->mm);
+       mmput(work->mm);
        kmem_cache_free(async_pf_cache, work);
        return 0;
 }