Re: [PATCH 7/7] vfio/pci: Remove map-on-fault behavior

[Christoph Hellwig]

On Thu, Aug 05, 2021 at 11:08:21AM -0600, Alex Williamson wrote:
> +void vfio_pci_test_and_up_write_memory_lock(struct vfio_pci_device *vdev)
> +{
> +	if (vdev->zapped_bars && __vfio_pci_memory_enabled(vdev)) {
> +		WARN_ON(vfio_device_io_remap_mapping_range(&vdev->vdev,
> +			VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_BAR0_REGION_INDEX),
> +			VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_ROM_REGION_INDEX) -
> +			VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_BAR0_REGION_INDEX)));
> +		vdev->zapped_bars = false;

Doing actual work inside a WARN_ON is pretty nasty.  Also the non-ONCE
version here will lead to massive log splatter if it actually hits.

I'd prefer something like:

	loff_t start = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_BAR0_REGION_INDEX);
	loff_t end = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_ROM_REGION_INDEX);

	if (vdev->zapped_bars && __vfio_pci_memory_enabled(vdev)) {
		if (!vfio_device_io_remap_mapping_range(&vdev->vdev, start,
				end - start))
			vdev->zapped_bars = false;
		WARN_ON_ONCE(vdev->zapped_bars);

>  	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> -	vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);

What is the story with this appearing earlier and disappearing here
again?

> +extern void vfio_pci_test_and_up_write_memory_lock(struct vfio_pci_device
> +						   *vdev);

No need for the extern.