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

On Tue, Sep 23, 2025 at 11:30:41AM -0600, Alex Williamson wrote:

On Tue, 23 Sep 2025 12:04:14 -0300
Jason Gunthorpe [off-list ref] wrote:

quoted

On Mon, Sep 22, 2025 at 03:00:32PM -0600, Alex Williamson wrote:

quoted

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