[Linaro-mm-sig] Re: [PATCH v4 02/10] PCI/P2PDMA: Add CONFIG_PCI_P2PDMA_CORE

On Wed, Jul 01, 2026 at 06:12:14PM +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 vfio-pci commit will rely 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), satisfying (1).

Then, when the original CONFIG_PCI_P2PDMA is set, drivers have access to the additional P2P features of (2). This still depends on CONFIG_ZONE_DEVICE.

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

Acked-by: Bjorn Helgaas bhelgaas@google.com

---

MAINTAINERS | 2 +- drivers/pci/Kconfig | 10 ++-- drivers/pci/Makefile | 1 + drivers/pci/p2pdma.c | 107 +-------------------------------- drivers/pci/p2pdma.h | 29 +++++++++ drivers/pci/p2pdma_core.c | 118 +++++++++++++++++++++++++++++++++++++ include/linux/pci-p2pdma.h | 24 ++++---- include/linux/pci.h | 2 +- 8 files changed, 171 insertions(+), 122 deletions(-) create mode 100644 drivers/pci/p2pdma.h create mode 100644 drivers/pci/p2pdma_core.c

diff --git a/MAINTAINERS b/MAINTAINERS index c8d4b913f26c..713861af4484 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -20626,7 +20626,7 @@ B: https://bugzilla.kernel.org C: irc://irc.oftc.net/linux-pci T: git git://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git F: Documentation/driver-api/pci/p2pdma.rst -F: drivers/pci/p2pdma.c +F: drivers/pci/p2pdma* F: include/linux/pci-p2pdma.h PCI POWER CONTROL diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig index 33c88432b728..59d70bc84cc9 100644 --- a/drivers/pci/Kconfig +++ b/drivers/pci/Kconfig @@ -206,11 +206,7 @@ config PCIE_TPH config PCI_P2PDMA bool "PCI peer-to-peer transfer support" depends on ZONE_DEVICE

• #
• # The need for the scatterlist DMA bus address flag means PCI P2PDMA
• # requires 64bit
• #
• depends on 64BIT

• select PCI_P2PDMA_CORE select GENERIC_ALLOCATOR select NEED_SG_DMA_FLAGS help

@@ -226,6 +222,10 @@ config PCI_P2PDMA If unsure, say N. +config PCI_P2PDMA_CORE

• default n
• bool

config PCI_LABEL def_bool y if (DMI || ACPI) select NLS diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile index 41ebc3b9a518..0b32572d57a1 100644 --- a/drivers/pci/Makefile +++ b/drivers/pci/Makefile @@ -30,6 +30,7 @@ obj-$(CONFIG_PCI_SYSCALL) += syscall.o obj-$(CONFIG_PCI_STUB) += pci-stub.o obj-$(CONFIG_PCI_PF_STUB) += pci-pf-stub.o obj-$(CONFIG_PCI_ECAM) += ecam.o +obj-$(CONFIG_PCI_P2PDMA_CORE) += p2pdma_core.o obj-$(CONFIG_PCI_P2PDMA) += p2pdma.o obj-$(CONFIG_XEN_PCIDEV_FRONTEND) += xen-pcifront.o obj-$(CONFIG_VGA_ARB) += vgaarb.o diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c index a5a1baebc34e..50b1a7daf55c 100644 --- a/drivers/pci/p2pdma.c +++ b/drivers/pci/p2pdma.c @@ -21,12 +21,7 @@ #include <linux/seq_buf.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];

-}; +#include "p2pdma.h" struct pci_p2pdma_pagemap { struct dev_pagemap pgmap; @@ -226,8 +221,7 @@ static const struct dev_pagemap_ops p2pdma_pgmap_ops = { .folio_free = p2pdma_folio_free, }; -static void pci_p2pdma_release_pool(struct pci_dev *pdev,

• 		    struct pci_p2pdma *p2pdma)
  

+void pci_p2pdma_release_pool(struct pci_dev *pdev, struct pci_p2pdma *p2pdma) { if (!p2pdma->pool) return; @@ -237,103 +231,6 @@ static void pci_p2pdma_release_pool(struct pci_dev *pdev, sysfs_remove_group(&pdev->dev.kobj, &p2pmem_group); } -static void pci_p2pdma_release(void *data) -{

• struct pci_dev *pdev = data;
• struct pci_p2pdma *p2pdma;
• p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
• if (!p2pdma)

• return;
  

• /* Flush and disable pci_alloc_p2p_mem() */
• pdev->p2pdma = NULL;
• pci_p2pdma_release_pool(pdev, p2pdma);
• xa_destroy(&p2pdma->map_types);

-}

-/**

• • pcim_p2pdma_init - Initialise peer-to-peer DMA providers
• • @pdev: The PCI device to enable P2PDMA for
• • This function initializes the peer-to-peer DMA infrastructure
• • for a PCI device. It allocates and sets up the necessary data
• • structures to support P2PDMA operations, including mapping type
• • tracking.
• */

-int pcim_p2pdma_init(struct pci_dev *pdev) -{

• struct pci_p2pdma *p2p;
• int i, ret;
• p2p = rcu_dereference_protected(pdev->p2pdma, 1);
• if (p2p)

• return 0;
  

• p2p = devm_kzalloc(&pdev->dev, sizeof(*p2p), GFP_KERNEL);
• if (!p2p)

• return -ENOMEM;
  

• xa_init(&p2p->map_types);
• /*

• * Iterate over all standard PCI BARs and record only those that
  

• * correspond to MMIO regions. Skip non-memory resources (e.g. I/O
  

• * port BARs) since they cannot be used for peer-to-peer (P2P)
  

• * transactions.
  

• */
  

• for (i = 0; i < PCI_STD_NUM_BARS; i++) {

• if (!(pci_resource_flags(pdev, i) & IORESOURCE_MEM))
  

• 	continue;
  

• p2p->mem[i].owner = &pdev->dev;
  

• p2p->mem[i].bus_offset =
  

• 	pci_bus_address(pdev, i) - pci_resource_start(pdev, i);
  

• }
• ret = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_release, pdev);
• if (ret)

• goto out_p2p;
  

• rcu_assign_pointer(pdev->p2pdma, p2p);
• return 0;

-out_p2p:

• devm_kfree(&pdev->dev, p2p);
• return ret;

-} -EXPORT_SYMBOL_GPL(pcim_p2pdma_init);

-/**

• • pcim_p2pdma_provider - Get peer-to-peer DMA provider
• • @pdev: The PCI device to enable P2PDMA for
• • @bar: BAR index to get provider
• • This function gets peer-to-peer DMA provider for a PCI device. The lifetime
• • of the provider (and of course the MMIO) is bound to the lifetime of the
• • driver. A driver calling this function must ensure that all references to the
• • provider, and any DMA mappings created for any MMIO, are all cleaned up
• • before the driver remove() completes.
• • Since P2P is almost always shared with a second driver this means some system
• • to notify, invalidate and revoke the MMIO's DMA must be in place to use this
• • function. For example a revoke can be built using DMABUF.
• */

-struct p2pdma_provider *pcim_p2pdma_provider(struct pci_dev *pdev, int bar) -{

• struct pci_p2pdma *p2p;
• if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))

• return NULL;
  

• p2p = rcu_dereference_protected(pdev->p2pdma, 1);
• if (WARN_ON(!p2p))

• /* Someone forgot to call to pcim_p2pdma_init() before */
  

• return NULL;
  

• return &p2p->mem[bar];

-} -EXPORT_SYMBOL_GPL(pcim_p2pdma_provider);

static int pci_p2pdma_setup_pool(struct pci_dev *pdev) { struct pci_p2pdma *p2pdma; diff --git a/drivers/pci/p2pdma.h b/drivers/pci/p2pdma.h new file mode 100644 index 000000000000..946383809981 --- /dev/null +++ b/drivers/pci/p2pdma.h @@ -0,0 +1,29 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/*

• • PCI peer-to-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)
  

+{ +} +#endif

+#endif diff --git a/drivers/pci/p2pdma_core.c b/drivers/pci/p2pdma_core.c new file mode 100644 index 000000000000..bb2138bf2bc7 --- /dev/null +++ b/drivers/pci/p2pdma_core.c @@ -0,0 +1,118 @@ +// SPDX-License-Identifier: GPL-2.0 +/*

• • PCI peer-to-peer DMA support core, providing a bare-bones
• • pcim_p2pdma_provider() interface to drivers even if full P2PDMA
• • isn't present. The full P2PDMA feature is in p2pdma.c (see
• • CONFIG_PCI_P2PDMA).
• • Copyright (c) 2016-2018, Logan Gunthorpe
• • Copyright (c) 2016-2017, Microsemi Corporation
• • Copyright (c) 2017, Christoph Hellwig
• • Copyright (c) 2018, Eideticom Inc.
• */

+#define pr_fmt(fmt) "pci-p2pdma: " fmt +#include <linux/ctype.h> +#include <linux/genalloc.h> +#include <linux/memremap.h> +#include <linux/pci-p2pdma.h> +#include <linux/xarray.h>

+#include "p2pdma.h"

+static void pci_p2pdma_release(void *data) +{

• struct pci_dev *pdev = data;
• struct pci_p2pdma *p2pdma;
• p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
• if (!p2pdma)

• return;
  

• /* Flush and disable pci_alloc_p2p_mem() */
• pdev->p2pdma = NULL;
• pci_p2pdma_release_pool(pdev, p2pdma);
• xa_destroy(&p2pdma->map_types);

+}

+/**

• • pcim_p2pdma_init - Initialise peer-to-peer DMA providers
• • @pdev: The PCI device to enable P2PDMA for
• • This function initializes the peer-to-peer DMA infrastructure
• • for a PCI device. It allocates and sets up the necessary data
• • structures to support P2PDMA operations, including mapping type
• • tracking.
• */

+int pcim_p2pdma_init(struct pci_dev *pdev) +{

• struct pci_p2pdma *p2p;
• int i, ret;
• p2p = rcu_dereference_protected(pdev->p2pdma, 1);
• if (p2p)

• return 0;
  

• p2p = devm_kzalloc(&pdev->dev, sizeof(*p2p), GFP_KERNEL);
• if (!p2p)

• return -ENOMEM;
  

• xa_init(&p2p->map_types);
• /*

• * Iterate over all standard PCI BARs and record only those that
  

• * correspond to MMIO regions. Skip non-memory resources (e.g. I/O
  

• * port BARs) since they cannot be used for peer-to-peer (P2P)
  

• * transactions.
  

• */
  

• for (i = 0; i < PCI_STD_NUM_BARS; i++) {

• if (!(pci_resource_flags(pdev, i) & IORESOURCE_MEM))
  

• 	continue;
  

• p2p->mem[i].owner = &pdev->dev;
  

• p2p->mem[i].bus_offset =
  

• 	pci_bus_address(pdev, i) - pci_resource_start(pdev, i);
  

• }
• ret = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_release, pdev);
• if (ret)

• goto out_p2p;
  

• rcu_assign_pointer(pdev->p2pdma, p2p);
• return 0;

+out_p2p:

• devm_kfree(&pdev->dev, p2p);
• return ret;

+} +EXPORT_SYMBOL_GPL(pcim_p2pdma_init);

+/**

• • pcim_p2pdma_provider - Get peer-to-peer DMA provider
• • @pdev: The PCI device to enable P2PDMA for
• • @bar: BAR index to get provider
• • This function gets peer-to-peer DMA provider for a PCI device. The lifetime
• • of the provider (and of course the MMIO) is bound to the lifetime of the
• • driver. A driver calling this function must ensure that all references to the
• • provider, and any DMA mappings created for any MMIO, are all cleaned up
• • before the driver remove() completes.
• • Since P2P is almost always shared with a second driver this means some system
• • to notify, invalidate and revoke the MMIO's DMA must be in place to use this
• • function. For example a revoke can be built using DMABUF.
• */

+struct p2pdma_provider *pcim_p2pdma_provider(struct pci_dev *pdev, int bar) +{

• struct pci_p2pdma *p2p;
• if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))

• return NULL;
  

• p2p = rcu_dereference_protected(pdev->p2pdma, 1);
• if (WARN_ON(!p2p))

• /* Someone forgot to call to pcim_p2pdma_init() before */
  

• return NULL;
  

• return &p2p->mem[bar];

+} +EXPORT_SYMBOL_GPL(pcim_p2pdma_provider); diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h index 873de20a2247..4c42a7b2ee85 100644 --- a/include/linux/pci-p2pdma.h +++ b/include/linux/pci-p2pdma.h @@ -67,9 +67,22 @@ enum pci_p2pdma_map_type { PCI_P2PDMA_MAP_THRU_HOST_BRIDGE, }; -#ifdef CONFIG_PCI_P2PDMA +#ifdef CONFIG_PCI_P2PDMA_CORE int pcim_p2pdma_init(struct pci_dev *pdev); struct p2pdma_provider *pcim_p2pdma_provider(struct pci_dev *pdev, int bar); +#else +static inline int pcim_p2pdma_init(struct pci_dev *pdev) +{

• return -EOPNOTSUPP;

+} +static inline struct p2pdma_provider *pcim_p2pdma_provider(struct pci_dev *pdev,

• 					   int bar)
  

+{

• return NULL;

+} +#endif

+#ifdef CONFIG_PCI_P2PDMA int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size, u64 offset); int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients, @@ -89,15 +102,6 @@ ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev, enum pci_p2pdma_map_type pci_p2pdma_map_type(struct p2pdma_provider *provider, struct device *dev); #else /* CONFIG_PCI_P2PDMA */ -static inline int pcim_p2pdma_init(struct pci_dev *pdev) -{

• return -EOPNOTSUPP;

-} -static inline struct p2pdma_provider *pcim_p2pdma_provider(struct pci_dev *pdev,

• 					   int bar)
  

-{

• return NULL;

-} static inline int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size, u64 offset) { diff --git a/include/linux/pci.h b/include/linux/pci.h index 2c4454583c11..531aec355686 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -557,7 +557,7 @@ struct pci_dev { u16 pasid_cap; /* PASID Capability offset */ u16 pasid_features; #endif -#ifdef CONFIG_PCI_P2PDMA +#ifdef CONFIG_PCI_P2PDMA_CORE struct pci_p2pdma __rcu *p2pdma; #endif

#ifdef CONFIG_PCI_DOE

2.50.1 (Apple Git-155)