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

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>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 10df100..06e6401 100644 (file)
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -101,7 +101,7 @@ 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);
 }
 
@@ -118,7 +118,7 @@ void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu)
                flush_work(&work->work);
 #else
                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);
                }
@@ -183,7 +183,7 @@ int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, unsigned long hva,
        work->addr = hva;
        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
@@ -201,7 +201,7 @@ int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, unsigned long hva,
        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;
 }