Re: [PATCH v2 03/10] PCI/P2PDMA: Refactor to separate core P2P functionality from memory allocation

Jason Gunthorpe
2025-09-23T17:43:40Z

On Tue, Sep 23, 2025 at 11:30:41AM -0600, Alex Williamson wrote:
> On Tue, 23 Sep 2025 12:04:14 -0300
> Jason Gunthorpe <jgg@nvidia.com> wrote:
>
> > On Mon, Sep 22, 2025 at 03:00:32PM -0600, Alex Williamson wrote:
> > > But then later in patch 8/ and again in 10/ why exactly do we cache
> > > the provider on the vfio_pci_core_device rather than ask for it on
> > > demand from the p2pdma?
> >
> > It makes the most sense if the P2P is activated once during probe(),
> > it is just a cheap memory allocation, so no reason not to.
> >
> > If you try to do it on-demand then it will require more locking.
>
> I'm only wondering about splitting to an "initialize/setup" function
> where providers for each BAR are setup, and a "get provider" interface,
> which doesn't really seem to be a hot path anyway. Batching could
> still be done to setup all BAR providers at once.

I agree it is a weird interface, but it is close to the existing weird
interface :\

> However, the setup isn't really once per probe(), even in the case of a
> new driver probing we re-use the previously setup providers.

It uses devm to call pci_p2pdma_release() which NULL's pdev->p2pdma.

Jason