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

Alex Williamson
2021-08-10T15:04:08Z

On Tue, 10 Aug 2021 11:11:49 +0200
Christoph Hellwig <hch@infradead.org> wrote:

> 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?

We switched from io_remap_pfn_range() which includes this flag
implicitly, to vmf_insert_pfn() which does not, and back to
io_remap_pfn_range() when the fault handler is removed.

> > +extern void vfio_pci_test_and_up_write_memory_lock(struct vfio_pci_device
> > + *vdev);
>
> No need for the extern.

Thanks much for the reviews!

Alex