On Tue, May 05, 2026 at 08:50:58AM -0600, Alex Williamson wrote: > On Tue, 5 May 2026 13:49:11 +0300 > Leon Romanovsky <[email protected]> wrote: > > > On Mon, May 04, 2026 at 04:40:41AM -0300, Jason Gunthorpe wrote: > > > On Fri, May 01, 2026 at 04:19:15PM -0600, Alex Williamson wrote: > > > > > > > Exporting dma-bufs from vfio-pci is a feature, but mmap of MMIO BARs is > > > > a legacy requirement. That legacy requirement now depends on > > > > PCI_P2PDMA, which depends on 64BIT and ZONE_DEVICE. > > > > > > That should be split up now, Leon missed it when he added the new > > > APIs that didn't require ZONE_DEVICE.. > > > > Sorry, what did I miss here? > > VFIO_DMABUF is an optional feature and is enabled only when P2P support is > > available. It does not affect legacy systems where P2P cannot be enabled. > > If we look at the long term view of moving exclusively to cdev/iommufd, > where VFIO_DMABUF becomes the mechanism for implementing P2P DMA > mappings, VFIO_DMABUF may be optional, but it's highly desirable for > legacy compatibility. There's an argument though that providing P2P > compatibility on platforms that support PCI_P2PDMA is probably > sufficient. > > However, in providing mmap of dmabufs as a feature, this series is > wiring all mmaps through dmabufs and therefore that dependency becomes > fundamental to the use of vfio-pci. Thus the discussion whether the > noted config requirements could be lifted. Thanks,
Right, there was no need to remove ZONE_DEVICE when I added my code, and I left the task of cleaning it out of is_pci_p2pdma_page() for another day. Without ZONE_DEVICE, all pages are treated as non‑P2P. > > Alex > > PS - Please also weigh in on the dmabuf underflow[1] > > [1]https://lore.kernel.org/all/[email protected]/ will do. Thanks
