On Tue, 5 May 2026 13:49:11 +0300 Leon Romanovsky leon@kernel.org 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,
Alex
PS - Please also weigh in on the dmabuf underflow[1]
[1]https://lore.kernel.org/all/20260501131236.278ac431@shazbot.org/