On Thu, Sep 16, 2021 at 05:40:59PM -0600, Logan Gunthorpe wrote:

> +static void pci_p2pdma_unmap_mappings(void *data)
> +{
> +     struct pci_dev *pdev = data;
> +     struct pci_p2pdma *p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
> +
> +     p2pdma->active = false;
> +     synchronize_rcu();
> +     unmap_mapping_range(p2pdma->inode->i_mapping, 0, 0, 1);
> +     pci_p2pdma_free_mappings(p2pdma->inode->i_mapping);
> +}

If this is going to rely on unmap_mapping_range then GUP should also
reject this memory for FOLL_LONGTERM..

What along this control flow:

> +       error = devm_add_action_or_reset(&pdev->dev, 
> pci_p2pdma_unmap_mappings,
> +                                        pdev);

Waits for all the page refcounts to go to zero?

Jason
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