Re: [PATCH v2 1/9] PCI/P2PDMA: Add CONFIG_PCI_P2PDMA_CORE

[Matt Evans]

Hi Logan,

On 27/05/2026 17:07, Logan Gunthorpe wrote:
> On 2026-05-27 04:23, Matt Evans wrote:
> > The P2PDMA code currently provides two features under the same
> > CONFIG_PCI_P2PDMA option:
> >
> >   1.  Locate providers via pcim_p2pdma_provider()
> >   2.  Manage actual P2P DMA
> >
> > Other code (such as vfio-pci) depends on 1, without having a hard
> > dependency on 2.
> >
> > A future commit expands the use of DMABUF in vfio-pci for non-P2P
> > scenarios, relying on pcim_p2pdma_provider() always being present.  If
> > that depended on CONFIG_PCI_P2PDMA, it would make vfio-pci only
> > available if CONFIG_ZONE_DEVICE is present (e.g. 64-bit systems), even
> > when P2P is not needed.
> >
> > To resolve this, introduce CONFIG_PCI_P2PDMA_CORE which contains the
> > basic provider functionality to make it available even if the
> > CONFIG_PCI_P2PDMA feature is disabled or unavailable due to
> > !CONFIG_ZONE_DEVICE.  Users such as vfio-pci can enable their own P2P
> > features based off the original CONFIG_PCI_P2PDMA (available when
> > CONFIG_ZONE_DEVICE is set).
> >
> > Signed-off-by: Matt Evans <mattev@xxxxxxxx>
>
> Largely this looks good to me. I have one minor nit below that you can
> apply or not. Either way, feel free to add:
>
> Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
>
>
> >   static void pci_p2pdma_release(void *data)
> >   {
> >   	struct pci_dev *pdev = data;
> > @@ -241,11 +251,13 @@ static void pci_p2pdma_release(void *data)
> >   		synchronize_rcu();
> >   	xa_destroy(&p2pdma->map_types);
> >   
> > +#ifdef CONFIG_PCI_P2PDMA
> >   	if (!p2pdma->pool)
> >   		return;
> >   
> >   	gen_pool_destroy(p2pdma->pool);
> >   	sysfs_remove_group(&pdev->dev.kobj, &p2pmem_group);
> > +#endif
> >   }
>
> I'm personally not a fan of adding #ifdefs inside functions like this.
> This instance is small and easy to understand, but it can quickly become
> a bit of a mess if we start adding more features. I probably would have
> created a pci_p2pdma_release_pool() helper which does the inverse of
> pci_p2pdma_setup_pool(), it would be called in pci_p2pdma_release() and
> an empty implementation would be provided in the case where
> CONFIG_PCI_P2PDMA is not set.

That's cleaner, I'll do that.  Thanks for the review.


Matt