[PATCH v3 1/9] PCI/P2PDMA: Add CONFIG_PCI_P2PDMA_CORE
From: Matt Evans
Date: Wed Jun 10 2026 - 12:02:22 EST
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@xxxxxxxxxx>
---
MAINTAINERS | 2 +-
drivers/pci/Kconfig | 10 ++--
drivers/pci/Makefile | 1 +
drivers/pci/p2pdma.c | 109 ++--------------------------------
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, 174 insertions(+), 121 deletions(-)
create mode 100644 drivers/pci/p2pdma.h
create mode 100644 drivers/pci/p2pdma_core.c
diff --git a/MAINTAINERS b/MAINTAINERS
index c2c6d79275c6..b21523b3bd8b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -20617,7 +20617,7 @@ 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 7c898542af8d..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;
@@ -226,110 +221,16 @@ static const struct dev_pagemap_ops p2pdma_pgmap_ops = {
.folio_free = p2pdma_folio_free,
};
-static void pci_p2pdma_release(void *data)
+void pci_p2pdma_release_pool(struct pci_dev *pdev, struct pci_p2pdma *p2pdma)
{
- 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;
- if (p2pdma->pool)
- synchronize_rcu();
- xa_destroy(&p2pdma->map_types);
-
if (!p2pdma->pool)
return;
+ synchronize_rcu();
gen_pool_destroy(p2pdma->pool);
sysfs_remove_group(&pdev->dev.kobj, &p2pmem_group);
}
-/**
- * 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;
@@ -932,8 +833,8 @@ void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size)
struct pci_p2pdma *p2pdma;
/*
- * Pairs with synchronize_rcu() in pci_p2pdma_release() to
- * ensure pdev->p2pdma is non-NULL for the duration of the
+ * Pairs with synchronize_rcu() in pci_p2pdma_release_pool()
+ * to ensure pdev->p2pdma is non-NULL for the duration of the
* read-lock.
*/
rcu_read_lock();
diff --git a/drivers/pci/p2pdma.h b/drivers/pci/p2pdma.h
new file mode 100644
index 000000000000..453f4aa7ade8
--- /dev/null
+++ 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)
+{
+}
+#endif
+
+#endif
+
diff --git a/drivers/pci/p2pdma_core.c b/drivers/pci/p2pdma_core.c
new file mode 100644
index 000000000000..1fda15d40196
--- /dev/null
+++ 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
+ * 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)