On 21/04/14 15:26, Oleg Nesterov wrote:
> 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@xxxxxxxxxx>
This looks fine, from what I can tell. The old code has the problem mentioned
in your patch description, so your version is probably better.
> ---
> virt/kvm/async_pf.c | 8 ++++----
> 1 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
> index 0ced4f3..cda703e 100644
> --- a/virt/kvm/async_pf.c
> +++ b/virt/kvm/async_pf.c
> @@ -99,7 +99,7 @@ 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);
> }
>
> @@ -116,7 +116,7 @@ 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);
> }
> @@ -181,7 +181,7 @@ 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
> @@ -199,7 +199,7 @@ 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;
> }
>
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