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>

1 files changed, 4 insertions, 4 deletions

diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 10df100c4514..06e6401d6ef4 100644
--- 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;
 }