Re: [PATCH v5 8/9] vfio/pci: Enable peer-to-peer DMA transactions by default

Jason Gunthorpe
2025-10-17T11:55:32Z

On Thu, Oct 16, 2025 at 11:32:59PM -0700, Christoph Hellwig wrote:
> On Mon, Oct 13, 2025 at 06:26:10PM +0300, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@nvidia.com>
> >
> > Make sure that all VFIO PCI devices have peer-to-peer capabilities
> > enables, so we would be able to export their MMIO memory through DMABUF,
>
> How do you know that they are safe to use with P2P?

All PCI devices are "safe" for P2P by spec. I've never heard of a
non-complaint device causing problems in this area.

The issue is always SOC support inside the CPU and that is delt with
inside the P2P subsystem logic.

If we ever see a problem it would be delt with by quirking the broken
device through pci-quirks and having the p2p subsystem refuse any p2p
with that device.

Jason