[PATCH v3 1/9] PCI/P2PDMA: Add CONFIG_PCI_P2PDMA_CORE

[Matt Evans <matt@ozlabs.org>]

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>
---
 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)