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

[Logan Gunthorpe]

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.

Logan