RE: [PATCH v8 09/11] vfio/pci: Enable peer-to-peer DMA transactions by default

Tian, Kevin
2025-11-19T00:01:41Z

> From: Alex Williamson <alex@shazbot.org>
> Sent: Wednesday, November 19, 2025 4:11 AM
>
> On Tue, 18 Nov 2025 07:18:36 +0000
> "Tian, Kevin" <kevin.tian@intel.com> wrote:
>
> > > From: Leon Romanovsky <leon@kernel.org>
> > > Sent: Tuesday, November 11, 2025 5:58 PM
> > >
> > > From: Leon Romanovsky <leonro@nvidia.com>
> >
> > not required with only your own s-o-b
> >
> > > @@ -2090,6 +2092,9 @@ int vfio_pci_core_init_dev(struct vfio_device
> > > *core_vdev)
> > > INIT_LIST_HEAD(&vdev->dummy_resources_list);
> > > INIT_LIST_HEAD(&vdev->ioeventfds_list);
> > > INIT_LIST_HEAD(&vdev->sriov_pfs_item);
> > > + ret = pcim_p2pdma_init(vdev->pdev);
> > > + if (ret && ret != -EOPNOTSUPP)
> > > + return ret;
> >
> > Reading the commit msg seems -EOPNOTSUPP is only returned for fake
> > PCI devices, otherwise it implies regression. better add a comment for it?
>
> I think the commit log is saying that if a device comes along that
> can't support this, we'd quirk the init path to return -EOPNOTSUPP for
> that particular device here. This path is currently used when
> !CONFIG_PCI_P2PDMA to make this error non-fatal to the device init.
>
> I don't see a regression if such a device comes along and while we
> could survive other types of failures by disabling p2pdma here, I think
> all such cases are sufficient rare out of memory cases to consider them
> catastrophic. Thanks,
>

ah yes. I read it inaccurately.