On Wed, Jun 10, 2026 at 04:43:15PM +0100, 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

Some drivers (such as vfio-pci) depend 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 and refactor the basic provider functionality into a new p2pdma_core.c file. This is available even if the CONFIG_PCI_P2PDMA feature is disabled (or unavailable due to !CONFIG_ZONE_DEVICE). Then, drivers can enable any additional P2P features with the original CONFIG_PCI_P2PDMA (available when CONFIG_ZONE_DEVICE is set).

Signed-off-by: Matt Evans matt@ozlabs.org

I thought this was going to be just a code move and new Kconfig option, but it involves a little more than that, e.g., adding pci_p2pdma_release_pool() and tweaking the RCU synchronization.

If possible, it would be nice to do that refactoring in a smaller preliminary patch so it's easier to review/bisect/etc and make this one a pure code move.

I guess CONFIG_PCI_P2PDMA_CORE selects just part 1 ("Locate providers via pcim_p2pdma_provider()"), right?

+++ b/drivers/pci/p2pdma.h @@ -0,0 +1,29 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/*

• • PCI Peer 2 Peer DMA support.
• */

+#ifndef _PCI_P2PDMA_H +#define _PCI_P2PDMA_H

+#include <linux/genalloc.h> +#include <linux/pci-p2pdma.h> +#include <linux/xarray.h>

+struct pci_p2pdma {

• struct gen_pool *pool;
• bool p2pmem_published;
• struct xarray map_types;
• struct p2pdma_provider mem[PCI_STD_NUM_BARS];

+};

+#ifdef CONFIG_PCI_P2PDMA +void pci_p2pdma_release_pool(struct pci_dev *pdev, struct pci_p2pdma *p2pdma); +#else +static inline void pci_p2pdma_release_pool(struct pci_dev *pdev, struct pci_p2pdma *p2pdma)

Wrap to fit in 80 columns like the rest of drivers/pci/

+{ +} +#endif

+#endif

Spurious blank line at end.

+++ b/drivers/pci/p2pdma_core.c @@ -0,0 +1,118 @@ +// SPDX-License-Identifier: GPL-2.0 +/*

• • PCI Peer 2 Peer DMA support core, providing a bare-bones

In this English text, I think I would spell out "Peer to Peer" instead of relying on the "2" homophone. Same in p2pdma.h.