[PATCH v6 00/13] Copy Offload in NVMe Fabrics with P2P PCI Memory

[PATCH v6 00/13] Copy Offload in NVMe Fabrics with P2P PCI Memory

[Logan Gunthorpe]

Hi Everyone,

Here is version 6 of the PCI P2PDMA patch set. This version makes
a few minor changes from v5 and is based on v4.19-rc3. A git repo is here:

https://github.com/sbates130272/linux-p2pmem pci-p2p-v6

Thanks,

Logan

--

Changes in v6:

* Rebased on v4.19-rc3

* Remove the changes to the common submit_bio() path and instead
  set REQ_NOMERGE in the NVME target driver, when appropriate.
  Per discussions with Jens and Christoph.

* Some minor grammar changes in the documentation as spotted by Randy.

Changes in v5:

* Rebased on v4.19-rc1

* Drop changing ACS settings in this patchset. Now, the code
  will only allow P2P transactions between devices whos
  downstream ports do not restrict P2P TLPs.

* Drop the REQ_PCI_P2PDMA block flag and instead use
  is_pci_p2pdma_page() to tell if a request is P2P or not. In that
  case we check for queue support and enforce using REQ_NOMERGE.
  Per feedback from Christoph.

* Drop the pci_p2pdma_unmap_sg() function as it was empty and only
  there for symmetry and compatibility with dma_unmap_sg. Per feedback
  from Christoph.

* Split off the logic to handle enabling P2P in NVMe fabrics' configfs
  into specific helpers in the p2pdma code. Per feedback from Christoph.

* A number of other minor cleanups and fixes as pointed out by
  Christoph and others.

Changes in v4:

* Change the original upstream_bridges_match() function to
  upstream_bridge_distance() which calculates the distance between two
  devices as long as they are behind the same root port. This should
  address Bjorn's concerns that the code was to focused on
  being behind a single switch.

* The disable ACS function now disables ACS for all bridge ports instead
  of switch ports (ie. those that had two upstream_bridge ports).

* Change the pci_p2pmem_alloc_sgl() and pci_p2pmem_free_sgl()
  API to be more like sgl_alloc() in that the alloc function returns
  the allocated scatterlist and nents is not required bythe free
  function.

* Moved the new documentation into the driver-api tree as requested
  by Jonathan

* Add SGL alloc and free helpers in the nvmet code so that the
  individual drivers can share the code that allocates P2P memory.
  As requested by Christoph.

* Cleanup the nvmet_p2pmem_store() function as Christoph
  thought my first attempt was ugly.

* Numerous commit message and comment fix-ups

Changes in v3:

* Many more fixes and minor cleanups that were spotted by Bjorn

* Additional explanation of the ACS change in both the commit message
  and Kconfig doc. Also, the code that disables the ACS bits is surrounded
  explicitly by an #ifdef

* Removed the flag we added to rdma_rw_ctx() in favour of using
  is_pci_p2pdma_page(), as suggested by Sagi.

* Adjust pci_p2pmem_find() so that it prefers P2P providers that
  are closest to (or the same as) the clients using them. In cases
  of ties, the provider is randomly chosen.

* Modify the NVMe Target code so that the PCI device name of the provider
  may be explicitly specified, bypassing the logic in pci_p2pmem_find().
  (Note: it's still enforced that the provider must be behind the
   same switch as the clients).

* As requested by Bjorn, added documentation for driver writers.


Changes in v2:

* Renamed everything to 'p2pdma' per the suggestion from Bjorn as well
  as a bunch of cleanup and spelling fixes he pointed out in the last
  series.

* To address Alex's ACS concerns, we change to a simpler method of
  just disabling ACS behind switches for any kernel that has
  CONFIG_PCI_P2PDMA.

* We also reject using devices that employ 'dma_virt_ops' which should
  fairly simply handle Jason's concerns that this work might break with
  the HFI, QIB and rxe drivers that use the virtual ops to implement
  their own special DMA operations.

--

This is a continuation of our work to enable using Peer-to-Peer PCI
memory in the kernel with initial support for the NVMe fabrics target
subsystem. Many thanks go to Christoph Hellwig who provided valuable
feedback to get these patches to where they are today.

The concept here is to use memory that's exposed on a PCI BAR as
data buffers in the NVMe target code such that data can be transferred
from an RDMA NIC to the special memory and then directly to an NVMe
device avoiding system memory entirely. The upside of this is better
QoS for applications running on the CPU utilizing memory and lower
PCI bandwidth required to the CPU (such that systems could be designed
with fewer lanes connected to the CPU).

Due to these trade-offs we've designed the system to only enable using
the PCI memory in cases where the NIC, NVMe devices and memory are all
behind the same PCI switch hierarchy. This will mean many setups that
could likely work well will not be supported so that we can be more
confident it will work and not place any responsibility on the user to
understand their topology. (We chose to go this route based on feedback
we received at the last LSF). Future work may enable these transfers
using a white list of known good root complexes. However, at this time,
there is no reliable way to ensure that Peer-to-Peer transactions are
permitted between PCI Root Ports.

For PCI P2P DMA transfers to work in this situation the ACS bits
must be disabled on the downstream ports (DSPs) for all devices
involved in the transfer. This can be done using the "disable_acs_redir"
PCI kernel command line option which was introduced in v4.19.

In order to enable PCI P2P functionality, we introduce a few new PCI
functions such that a driver can register P2P memory with the system.
Struct pages are created for this memory using devm_memremap_pages()
and the PCI bus offset is stored in the corresponding pagemap structure.

Another set of functions allow a client driver to create a list of
client devices that will be used in a given P2P transactions and then
use that list to find any P2P memory that is supported by all the
client devices.

In the block layer, we also introduce a flag for a request queue
to indicate a given queue supports targeting P2P memory. The driver
submitting bios must ensure that the queue supports P2P before
attempting to submit BIOs backed by P2P memory. Also, P2P requests
are marked to not be merged seeing a non-homogenous request would
complicate the DMA mapping requirements.

In the PCI NVMe driver, we modify the existing CMB support to utilize
the new PCI P2P memory infrastructure and also add support for P2P
memory in its request queue. When a P2P request is received it uses the
pci_p2pmem_map_sg() function which applies the necessary transformation
to get the corrent pci_bus_addr_t for the DMA transactions.

In the RDMA core, we also adjust rdma_rw_ctx_init() and
rdma_rw_ctx_destroy() to take a flags argument which indicates whether
to use the PCI P2P mapping functions or not. To avoid odd RDMA devices
that don't use the proper DMA infrastructure this code rejects using
any device that employs the virt_dma_ops implementation.

Finally, in the NVMe fabrics target port we introduce a new
configuration attribute: 'p2pmem'. When set to a true boolean, the port
will attempt to find P2P memory supported by the RDMA NIC and all namespaces.
It may also be set to a PCI device name to select a specific P2P
memory to use. If supported memory is found, it will be used in all IO
transfers. And if a port is using P2P memory, adding new namespaces that
are not supported by that memory will fail.

These patches have been tested on a number of Intel based systems and
for a variety of RDMA NICs (Mellanox, Broadcomm, Chelsio) and NVMe
SSDs (Intel, Seagate, Samsung) and p2pdma devices (Eideticom,
Microsemi, Chelsio and Everspin) using switches from both Microsemi
and Broadcomm.

--

Logan Gunthorpe (13):
  PCI/P2PDMA: Support peer-to-peer memory
  PCI/P2PDMA: Add sysfs group to display p2pmem stats
  PCI/P2PDMA: Add PCI p2pmem DMA mappings to adjust the bus offset
  PCI/P2PDMA: Introduce configfs/sysfs enable attribute helpers
  docs-rst: Add a new directory for PCI documentation
  PCI/P2PDMA: Add P2P DMA driver writer's documentation
  block: Add PCI P2P flag for request queue and check support for
    requests
  IB/core: Ensure we map P2P memory correctly in
    rdma_rw_ctx_[init|destroy]()
  nvme-pci: Use PCI p2pmem subsystem to manage the CMB
  nvme-pci: Add support for P2P memory in requests
  nvme-pci: Add a quirk for a pseudo CMB
  nvmet: Introduce helper functions to allocate and free request SGLs
  nvmet: Optionally use PCI P2P memory

 Documentation/ABI/testing/sysfs-bus-pci    |  25 +
 Documentation/driver-api/index.rst         |   2 +-
 Documentation/driver-api/pci/index.rst     |  21 +
 Documentation/driver-api/pci/p2pdma.rst    | 170 ++++
 Documentation/driver-api/{ => pci}/pci.rst |   0
 drivers/infiniband/core/rw.c               |  11 +-
 drivers/nvme/host/core.c                   |   4 +
 drivers/nvme/host/nvme.h                   |   8 +
 drivers/nvme/host/pci.c                    | 121 ++-
 drivers/nvme/target/configfs.c             |  36 +
 drivers/nvme/target/core.c                 | 154 ++++
 drivers/nvme/target/io-cmd-bdev.c          |   3 +
 drivers/nvme/target/nvmet.h                |  15 +
 drivers/nvme/target/rdma.c                 |  22 +-
 drivers/pci/Kconfig                        |  17 +
 drivers/pci/Makefile                       |   1 +
 drivers/pci/p2pdma.c                       | 941 +++++++++++++++++++++
 include/linux/blkdev.h                     |   3 +
 include/linux/memremap.h                   |   6 +
 include/linux/mm.h                         |  18 +
 include/linux/pci-p2pdma.h                 | 124 +++
 include/linux/pci.h                        |   4 +
 22 files changed, 1652 insertions(+), 54 deletions(-)
 create mode 100644 Documentation/driver-api/pci/index.rst
 create mode 100644 Documentation/driver-api/pci/p2pdma.rst
 rename Documentation/driver-api/{ => pci}/pci.rst (100%)
 create mode 100644 drivers/pci/p2pdma.c
 create mode 100644 include/linux/pci-p2pdma.h

--
2.19.0

[PATCH v6 01/13] PCI/P2PDMA: Support peer-to-peer memory

[Logan Gunthorpe]

Some PCI devices may have memory mapped in a BAR space that's
intended for use in peer-to-peer transactions. In order to enable
such transactions the memory must be registered with ZONE_DEVICE pages
so it can be used by DMA interfaces in existing drivers.

Add an interface for other subsystems to find and allocate chunks of P2P
memory as necessary to facilitate transfers between two PCI peers:

int pci_p2pdma_add_client();
struct pci_dev *pci_p2pmem_find();
void *pci_alloc_p2pmem();

The new interface requires a driver to collect a list of client devices
involved in the transaction with the pci_p2pmem_add_client*() functions
then call pci_p2pmem_find() to obtain any suitable P2P memory. Once
this is done the list is bound to the memory and the calling driver is
free to add and remove clients as necessary (adding incompatible clients
will fail). With a suitable p2pmem device, memory can then be
allocated with pci_alloc_p2pmem() for use in DMA transactions.

Depending on hardware, using peer-to-peer memory may reduce the bandwidth
of the transfer but can significantly reduce pressure on system memory.
This may be desirable in many cases: for example a system could be designed
with a small CPU connected to a PCIe switch by a small number of lanes
which would maximize the number of lanes available to connect to NVMe
devices.

The code is designed to only utilize the p2pmem device if all the devices
involved in a transfer are behind the same PCI bridge. This is because we
have no way of knowing whether peer-to-peer routing between PCIe Root Ports
is supported (PCIe r4.0, sec 1.3.1). Additionally, the benefits of P2P
transfers that go through the RC is limited to only reducing DRAM usage
and, in some cases, coding convenience. The PCI-SIG may be exploring
adding a new capability bit to advertise whether this is possible for
future hardware.

This commit includes significant rework and feedback from Christoph
Hellwig.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
 drivers/pci/Kconfig        |  17 +
 drivers/pci/Makefile       |   1 +
 drivers/pci/p2pdma.c       | 761 +++++++++++++++++++++++++++++++++++++
 include/linux/memremap.h   |   5 +
 include/linux/mm.h         |  18 +
 include/linux/pci-p2pdma.h | 102 +++++
 include/linux/pci.h        |   4 +
 7 files changed, 908 insertions(+)
 create mode 100644 drivers/pci/p2pdma.c
 create mode 100644 include/linux/pci-p2pdma.h

diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
index 56ff8f6d31fc..deb68be4fdac 100644
--- a/drivers/pci/Kconfig
+++ b/drivers/pci/Kconfig
@@ -132,6 +132,23 @@ config PCI_PASID
 
 	  If unsure, say N.
 
+config PCI_P2PDMA
+	bool "PCI peer-to-peer transfer support"
+	depends on PCI && ZONE_DEVICE
+	select GENERIC_ALLOCATOR
+	help
+	  Enableѕ drivers to do PCI peer-to-peer transactions to and from
+	  BARs that are exposed in other devices that are the part of
+	  the hierarchy where peer-to-peer DMA is guaranteed by the PCI
+	  specification to work (ie. anything below a single PCI bridge).
+
+	  Many PCIe root complexes do not support P2P transactions and
+	  it's hard to tell which support it at all, so at this time,
+	  P2P DMA transations must be between devices behind the same root
+	  port.
+
+	  If unsure, say N.
+
 config PCI_LABEL
 	def_bool y if (DMI || ACPI)
 	depends on PCI
diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile
index 1b2cfe51e8d7..85f4a703b2be 100644
--- a/drivers/pci/Makefile
+++ b/drivers/pci/Makefile
@@ -26,6 +26,7 @@ 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-$(CONFIG_PCI_P2PDMA)	+= p2pdma.o
 obj-$(CONFIG_XEN_PCIDEV_FRONTEND) += xen-pcifront.o
 
 # Endpoint library must be initialized before its users
diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
new file mode 100644
index 000000000000..88aaec5351cd
--- /dev/null
+++ b/drivers/pci/p2pdma.c
@@ -0,0 +1,761 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * PCI Peer 2 Peer DMA support.
+ *
+ * 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/pci-p2pdma.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/genalloc.h>
+#include <linux/memremap.h>
+#include <linux/percpu-refcount.h>
+#include <linux/random.h>
+#include <linux/seq_buf.h>
+
+struct pci_p2pdma {
+	struct percpu_ref devmap_ref;
+	struct completion devmap_ref_done;
+	struct gen_pool *pool;
+	bool p2pmem_published;
+};
+
+static void pci_p2pdma_percpu_release(struct percpu_ref *ref)
+{
+	struct pci_p2pdma *p2p =
+		container_of(ref, struct pci_p2pdma, devmap_ref);
+
+	complete_all(&p2p->devmap_ref_done);
+}
+
+static void pci_p2pdma_percpu_kill(void *data)
+{
+	struct percpu_ref *ref = data;
+
+	if (percpu_ref_is_dying(ref))
+		return;
+
+	percpu_ref_kill(ref);
+}
+
+static void pci_p2pdma_release(void *data)
+{
+	struct pci_dev *pdev = data;
+
+	if (!pdev->p2pdma)
+		return;
+
+	wait_for_completion(&pdev->p2pdma->devmap_ref_done);
+	percpu_ref_exit(&pdev->p2pdma->devmap_ref);
+
+	gen_pool_destroy(pdev->p2pdma->pool);
+	pdev->p2pdma = NULL;
+}
+
+static int pci_p2pdma_setup(struct pci_dev *pdev)
+{
+	int error = -ENOMEM;
+	struct pci_p2pdma *p2p;
+
+	p2p = devm_kzalloc(&pdev->dev, sizeof(*p2p), GFP_KERNEL);
+	if (!p2p)
+		return -ENOMEM;
+
+	p2p->pool = gen_pool_create(PAGE_SHIFT, dev_to_node(&pdev->dev));
+	if (!p2p->pool)
+		goto out;
+
+	init_completion(&p2p->devmap_ref_done);
+	error = percpu_ref_init(&p2p->devmap_ref,
+			pci_p2pdma_percpu_release, 0, GFP_KERNEL);
+	if (error)
+		goto out_pool_destroy;
+
+	percpu_ref_switch_to_atomic_sync(&p2p->devmap_ref);
+
+	error = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_release, pdev);
+	if (error)
+		goto out_pool_destroy;
+
+	pdev->p2pdma = p2p;
+
+	return 0;
+
+out_pool_destroy:
+	gen_pool_destroy(p2p->pool);
+out:
+	devm_kfree(&pdev->dev, p2p);
+	return error;
+}
+
+/**
+ * pci_p2pdma_add_resource - add memory for use as p2p memory
+ * @pdev: the device to add the memory to
+ * @bar: PCI BAR to add
+ * @size: size of the memory to add, may be zero to use the whole BAR
+ * @offset: offset into the PCI BAR
+ *
+ * The memory will be given ZONE_DEVICE struct pages so that it may
+ * be used with any DMA request.
+ */
+int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
+			    u64 offset)
+{
+	struct dev_pagemap *pgmap;
+	void *addr;
+	int error;
+
+	if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))
+		return -EINVAL;
+
+	if (offset >= pci_resource_len(pdev, bar))
+		return -EINVAL;
+
+	if (!size)
+		size = pci_resource_len(pdev, bar) - offset;
+
+	if (size + offset > pci_resource_len(pdev, bar))
+		return -EINVAL;
+
+	if (!pdev->p2pdma) {
+		error = pci_p2pdma_setup(pdev);
+		if (error)
+			return error;
+	}
+
+	pgmap = devm_kzalloc(&pdev->dev, sizeof(*pgmap), GFP_KERNEL);
+	if (!pgmap)
+		return -ENOMEM;
+
+	pgmap->res.start = pci_resource_start(pdev, bar) + offset;
+	pgmap->res.end = pgmap->res.start + size - 1;
+	pgmap->res.flags = pci_resource_flags(pdev, bar);
+	pgmap->ref = &pdev->p2pdma->devmap_ref;
+	pgmap->type = MEMORY_DEVICE_PCI_P2PDMA;
+
+	addr = devm_memremap_pages(&pdev->dev, pgmap);
+	if (IS_ERR(addr)) {
+		error = PTR_ERR(addr);
+		goto pgmap_free;
+	}
+
+	error = gen_pool_add_virt(pdev->p2pdma->pool, (unsigned long)addr,
+			pci_bus_address(pdev, bar) + offset,
+			resource_size(&pgmap->res), dev_to_node(&pdev->dev));
+	if (error)
+		goto pgmap_free;
+
+	error = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_percpu_kill,
+					  &pdev->p2pdma->devmap_ref);
+	if (error)
+		goto pgmap_free;
+
+	pci_info(pdev, "added peer-to-peer DMA memory %pR\n",
+		 &pgmap->res);
+
+	return 0;
+
+pgmap_free:
+	devres_free(pgmap);
+	return error;
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_add_resource);
+
+static struct pci_dev *find_parent_pci_dev(struct device *dev)
+{
+	struct device *parent;
+
+	dev = get_device(dev);
+
+	while (dev) {
+		if (dev_is_pci(dev))
+			return to_pci_dev(dev);
+
+		parent = get_device(dev->parent);
+		put_device(dev);
+		dev = parent;
+	}
+
+	return NULL;
+}
+
+/*
+ * Check if a PCI bridge has it's ACS redirection bits set to redirect P2P
+ * TLPs upstream via ACS. Returns 1 if the packets will be redirected
+ * upstream, 0 otherwise.
+ */
+static int pci_bridge_has_acs_redir(struct pci_dev *dev)
+{
+	int pos;
+	u16 ctrl;
+
+	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS);
+	if (!pos)
+		return 0;
+
+	pci_read_config_word(dev, pos + PCI_ACS_CTRL, &ctrl);
+
+	if (ctrl & (PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_EC))
+		return 1;
+
+	return 0;
+}
+
+static void seq_buf_print_bus_devfn(struct seq_buf *buf, struct pci_dev *dev)
+{
+	if (!buf)
+		return;
+
+	seq_buf_printf(buf, "%04x:%02x:%02x.%x;", pci_domain_nr(dev->bus),
+		       dev->bus->number, PCI_SLOT(dev->devfn),
+		       PCI_FUNC(dev->devfn));
+}
+
+/*
+ * Find the distance through the nearest common upstream bridge between
+ * two PCI devices.
+ *
+ * If the two devices are the same device then 0 will be returned.
+ *
+ * If there are two virtual functions of the same device behind the same
+ * bridge port then 2 will be returned (one step down to the PCIe switch,
+ * then one step back to the same device).
+ *
+ * In the case where two devices are connected to the same PCIe switch, the
+ * value 4 will be returned. This corresponds to the following PCI tree:
+ *
+ *     -+  Root Port
+ *      \+ Switch Upstream Port
+ *       +-+ Switch Downstream Port
+ *       + \- Device A
+ *       \-+ Switch Downstream Port
+ *         \- Device B
+ *
+ * The distance is 4 because we traverse from Device A through the downstream
+ * port of the switch, to the common upstream port, back up to the second
+ * downstream port and then to Device B.
+ *
+ * Any two devices that don't have a common upstream bridge will return -1.
+ * In this way devices on separate PCIe root ports will be rejected, which
+ * is what we want for peer-to-peer seeing each PCIe root port defines a
+ * separate hierarchy domain and there's no way to determine whether the root
+ * complex supports forwarding between them.
+ *
+ * In the case where two devices are connected to different PCIe switches,
+ * this function will still return a positive distance as long as both
+ * switches evenutally have a common upstream bridge. Note this covers
+ * the case of using multiple PCIe switches to achieve a desired level of
+ * fan-out from a root port. The exact distance will be a function of the
+ * number of switches between Device A and Device B.
+ *
+ * If a bridge which has any ACS redirection bits set is in the path
+ * then this functions will return -2. This is so we reject any
+ * cases where the TLPs are forwarded up into the root complex.
+ * In this case, a list of all infringing bridge addresses will be
+ * populated in acs_list (assuming it's non-null) for printk purposes.
+ */
+static int upstream_bridge_distance(struct pci_dev *a,
+				    struct pci_dev *b,
+				    struct seq_buf *acs_list)
+{
+	int dist_a = 0;
+	int dist_b = 0;
+	struct pci_dev *bb = NULL;
+	int acs_cnt = 0;
+
+	/*
+	 * Note, we don't need to take references to devices returned by
+	 * pci_upstream_bridge() seeing we hold a reference to a child
+	 * device which will already hold a reference to the upstream bridge.
+	 */
+
+	while (a) {
+		dist_b = 0;
+
+		if (pci_bridge_has_acs_redir(a)) {
+			seq_buf_print_bus_devfn(acs_list, a);
+			acs_cnt++;
+		}
+
+		bb = b;
+
+		while (bb) {
+			if (a == bb)
+				goto check_b_path_acs;
+
+			bb = pci_upstream_bridge(bb);
+			dist_b++;
+		}
+
+		a = pci_upstream_bridge(a);
+		dist_a++;
+	}
+
+	return -1;
+
+check_b_path_acs:
+	bb = b;
+
+	while (bb) {
+		if (a == bb)
+			break;
+
+		if (pci_bridge_has_acs_redir(bb)) {
+			seq_buf_print_bus_devfn(acs_list, bb);
+			acs_cnt++;
+		}
+
+		bb = pci_upstream_bridge(bb);
+	}
+
+	if (acs_cnt)
+		return -2;
+
+	return dist_a + dist_b;
+}
+
+static int upstream_bridge_distance_warn(struct pci_dev *provider,
+					 struct pci_dev *client)
+{
+	struct seq_buf acs_list;
+	int ret;
+
+	seq_buf_init(&acs_list, kmalloc(PAGE_SIZE, GFP_KERNEL), PAGE_SIZE);
+
+	ret = upstream_bridge_distance(provider, client, &acs_list);
+	if (ret == -2) {
+		pci_warn(client, "cannot be used for peer-to-peer DMA as ACS redirect is set between the client and provider\n");
+		/* Drop final semicolon */
+		acs_list.buffer[acs_list.len-1] = 0;
+		pci_warn(client, "to disable ACS redirect for this path, add the kernel parameter: pci=disable_acs_redir=%s\n",
+			 acs_list.buffer);
+
+	} else if (ret < 0) {
+		pci_warn(client, "cannot be used for peer-to-peer DMA as the client and provider do not share an upstream bridge\n");
+	}
+
+	kfree(acs_list.buffer);
+
+	return ret;
+}
+
+struct pci_p2pdma_client {
+	struct list_head list;
+	struct pci_dev *client;
+	struct pci_dev *provider;
+};
+
+/**
+ * pci_p2pdma_add_client - allocate a new element in a client device list
+ * @head: list head of p2pdma clients
+ * @dev: device to add to the list
+ *
+ * This adds @dev to a list of clients used by a p2pdma device.
+ * This list should be passed to pci_p2pmem_find(). Once pci_p2pmem_find() has
+ * been called successfully, the list will be bound to a specific p2pdma
+ * device and new clients can only be added to the list if they are
+ * supported by that p2pdma device.
+ *
+ * The caller is expected to have a lock which protects @head as necessary
+ * so that none of the pci_p2p functions can be called concurrently
+ * on that list.
+ *
+ * Returns 0 if the client was successfully added.
+ */
+int pci_p2pdma_add_client(struct list_head *head, struct device *dev)
+{
+	struct pci_p2pdma_client *item, *new_item;
+	struct pci_dev *provider = NULL;
+	struct pci_dev *client;
+	int ret;
+
+	if (IS_ENABLED(CONFIG_DMA_VIRT_OPS) && dev->dma_ops == &dma_virt_ops) {
+		dev_warn(dev, "cannot be used for peer-to-peer DMA because the driver makes use of dma_virt_ops\n");
+		return -ENODEV;
+	}
+
+	client = find_parent_pci_dev(dev);
+	if (!client) {
+		dev_warn(dev, "cannot be used for peer-to-peer DMA as it is not a PCI device\n");
+		return -ENODEV;
+	}
+
+	item = list_first_entry_or_null(head, struct pci_p2pdma_client, list);
+	if (item && item->provider) {
+		provider = item->provider;
+
+		ret = upstream_bridge_distance_warn(provider, client);
+		if (ret < 0) {
+			ret = -EXDEV;
+			goto put_client;
+		}
+	}
+
+	new_item = kzalloc(sizeof(*new_item), GFP_KERNEL);
+	if (!new_item) {
+		ret = -ENOMEM;
+		goto put_client;
+	}
+
+	new_item->client = client;
+	new_item->provider = pci_dev_get(provider);
+
+	list_add_tail(&new_item->list, head);
+
+	return 0;
+
+put_client:
+	pci_dev_put(client);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_add_client);
+
+static void pci_p2pdma_client_free(struct pci_p2pdma_client *item)
+{
+	list_del(&item->list);
+	pci_dev_put(item->client);
+	pci_dev_put(item->provider);
+	kfree(item);
+}
+
+/**
+ * pci_p2pdma_remove_client - remove and free a p2pdma client
+ * @head: list head of p2pdma clients
+ * @dev: device to remove from the list
+ *
+ * This removes @dev from a list of clients used by a p2pdma device.
+ * The caller is expected to have a lock which protects @head as necessary
+ * so that none of the pci_p2p functions can be called concurrently
+ * on that list.
+ */
+void pci_p2pdma_remove_client(struct list_head *head, struct device *dev)
+{
+	struct pci_p2pdma_client *pos, *tmp;
+	struct pci_dev *pdev;
+
+	pdev = find_parent_pci_dev(dev);
+	if (!pdev)
+		return;
+
+	list_for_each_entry_safe(pos, tmp, head, list) {
+		if (pos->client != pdev)
+			continue;
+
+		pci_p2pdma_client_free(pos);
+	}
+
+	pci_dev_put(pdev);
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_remove_client);
+
+/**
+ * pci_p2pdma_client_list_free - free an entire list of p2pdma clients
+ * @head: list head of p2pdma clients
+ *
+ * This removes all devices in a list of clients used by a p2pdma device.
+ * The caller is expected to have a lock which protects @head as necessary
+ * so that none of the pci_p2pdma functions can be called concurrently
+ * on that list.
+ */
+void pci_p2pdma_client_list_free(struct list_head *head)
+{
+	struct pci_p2pdma_client *pos, *tmp;
+
+	list_for_each_entry_safe(pos, tmp, head, list)
+		pci_p2pdma_client_free(pos);
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_client_list_free);
+
+/**
+ * pci_p2pdma_distance - Determive the cumulative distance between
+ *	a p2pdma provider and the clients in use.
+ * @provider: p2pdma provider to check against the client list
+ * @clients: list of devices to check (NULL-terminated)
+ * @verbose: if true, print warnings for devices when we return -1
+ *
+ * Returns -1 if any of the clients are not compatible (behind the same
+ * root port as the provider), otherwise returns a positive number where
+ * the lower number is the preferrable choice. (If there's one client
+ * that's the same as the provider it will return 0, which is best choice).
+ *
+ * For now, "compatible" means the provider and the clients are all behind
+ * the same PCI root port. This cuts out cases that may work but is safest
+ * for the user. Future work can expand this to white-list root complexes that
+ * can safely forward between each ports.
+ */
+int pci_p2pdma_distance(struct pci_dev *provider, struct list_head *clients,
+			bool verbose)
+{
+	struct pci_p2pdma_client *pos;
+	int ret;
+	int distance = 0;
+	bool not_supported = false;
+
+	if (list_empty(clients))
+		return -1;
+
+	list_for_each_entry(pos, clients, list) {
+		if (verbose)
+			ret = upstream_bridge_distance_warn(provider,
+							    pos->client);
+		else
+			ret = upstream_bridge_distance(provider, pos->client,
+						       NULL);
+
+		if (ret < 0)
+			not_supported = true;
+
+		if (not_supported && !verbose)
+			break;
+
+		distance += ret;
+	}
+
+	if (not_supported)
+		return -1;
+
+	return distance;
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_distance);
+
+/**
+ * pci_p2pdma_assign_provider - Check compatibily (as per pci_p2pdma_distance)
+ *	and assign a provider to a list of clients
+ * @provider: p2pdma provider to assign to the client list
+ * @clients: list of devices to check (NULL-terminated)
+ *
+ * Returns false if any of the clients are not compatible, true if the
+ * provider was successfully assigned to the clients.
+ */
+bool pci_p2pdma_assign_provider(struct pci_dev *provider,
+				struct list_head *clients)
+{
+	struct pci_p2pdma_client *pos;
+
+	if (pci_p2pdma_distance(provider, clients, true) < 0)
+		return false;
+
+	list_for_each_entry(pos, clients, list)
+		pos->provider = provider;
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_assign_provider);
+
+/**
+ * pci_has_p2pmem - check if a given PCI device has published any p2pmem
+ * @pdev: PCI device to check
+ */
+bool pci_has_p2pmem(struct pci_dev *pdev)
+{
+	return pdev->p2pdma && pdev->p2pdma->p2pmem_published;
+}
+EXPORT_SYMBOL_GPL(pci_has_p2pmem);
+
+/**
+ * pci_p2pmem_find - find a peer-to-peer DMA memory device compatible with
+ *	the specified list of clients and shortest distance (as determined
+ *	by pci_p2pmem_dma())
+ * @clients: list of devices to check (NULL-terminated)
+ *
+ * If multiple devices are behind the same switch, the one "closest" to the
+ * client devices in use will be chosen first. (So if one of the providers are
+ * the same as one of the clients, that provider will be used ahead of any
+ * other providers that are unrelated). If multiple providers are an equal
+ * distance away, one will be chosen at random.
+ *
+ * Returns a pointer to the PCI device with a reference taken (use pci_dev_put
+ * to return the reference) or NULL if no compatible device is found. The
+ * found provider will also be assigned to the client list.
+ */
+struct pci_dev *pci_p2pmem_find(struct list_head *clients)
+{
+	struct pci_dev *pdev = NULL;
+	struct pci_p2pdma_client *pos;
+	int distance;
+	int closest_distance = INT_MAX;
+	struct pci_dev **closest_pdevs;
+	int dev_cnt = 0;
+	const int max_devs = PAGE_SIZE / sizeof(*closest_pdevs);
+	int i;
+
+	closest_pdevs = kmalloc(PAGE_SIZE, GFP_KERNEL);
+
+	while ((pdev = pci_get_device(PCI_ANY_ID, PCI_ANY_ID, pdev))) {
+		if (!pci_has_p2pmem(pdev))
+			continue;
+
+		distance = pci_p2pdma_distance(pdev, clients, false);
+		if (distance < 0 || distance > closest_distance)
+			continue;
+
+		if (distance == closest_distance && dev_cnt >= max_devs)
+			continue;
+
+		if (distance < closest_distance) {
+			for (i = 0; i < dev_cnt; i++)
+				pci_dev_put(closest_pdevs[i]);
+
+			dev_cnt = 0;
+			closest_distance = distance;
+		}
+
+		closest_pdevs[dev_cnt++] = pci_dev_get(pdev);
+	}
+
+	if (dev_cnt)
+		pdev = pci_dev_get(closest_pdevs[prandom_u32_max(dev_cnt)]);
+
+	for (i = 0; i < dev_cnt; i++)
+		pci_dev_put(closest_pdevs[i]);
+
+	if (pdev)
+		list_for_each_entry(pos, clients, list)
+			pos->provider = pdev;
+
+	kfree(closest_pdevs);
+	return pdev;
+}
+EXPORT_SYMBOL_GPL(pci_p2pmem_find);
+
+/**
+ * pci_alloc_p2p_mem - allocate peer-to-peer DMA memory
+ * @pdev: the device to allocate memory from
+ * @size: number of bytes to allocate
+ *
+ * Returns the allocated memory or NULL on error.
+ */
+void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size)
+{
+	void *ret;
+
+	if (unlikely(!pdev->p2pdma))
+		return NULL;
+
+	if (unlikely(!percpu_ref_tryget_live(&pdev->p2pdma->devmap_ref)))
+		return NULL;
+
+	ret = (void *)gen_pool_alloc(pdev->p2pdma->pool, size);
+
+	if (unlikely(!ret))
+		percpu_ref_put(&pdev->p2pdma->devmap_ref);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(pci_alloc_p2pmem);
+
+/**
+ * pci_free_p2pmem - allocate peer-to-peer DMA memory
+ * @pdev: the device the memory was allocated from
+ * @addr: address of the memory that was allocated
+ * @size: number of bytes that was allocated
+ */
+void pci_free_p2pmem(struct pci_dev *pdev, void *addr, size_t size)
+{
+	gen_pool_free(pdev->p2pdma->pool, (uintptr_t)addr, size);
+	percpu_ref_put(&pdev->p2pdma->devmap_ref);
+}
+EXPORT_SYMBOL_GPL(pci_free_p2pmem);
+
+/**
+ * pci_virt_to_bus - return the PCI bus address for a given virtual
+ *	address obtained with pci_alloc_p2pmem()
+ * @pdev: the device the memory was allocated from
+ * @addr: address of the memory that was allocated
+ */
+pci_bus_addr_t pci_p2pmem_virt_to_bus(struct pci_dev *pdev, void *addr)
+{
+	if (!addr)
+		return 0;
+	if (!pdev->p2pdma)
+		return 0;
+
+	/*
+	 * Note: when we added the memory to the pool we used the PCI
+	 * bus address as the physical address. So gen_pool_virt_to_phys()
+	 * actually returns the bus address despite the misleading name.
+	 */
+	return gen_pool_virt_to_phys(pdev->p2pdma->pool, (unsigned long)addr);
+}
+EXPORT_SYMBOL_GPL(pci_p2pmem_virt_to_bus);
+
+/**
+ * pci_p2pmem_alloc_sgl - allocate peer-to-peer DMA memory in a scatterlist
+ * @pdev: the device to allocate memory from
+ * @sgl: the allocated scatterlist
+ * @nents: the number of SG entries in the list
+ * @length: number of bytes to allocate
+ *
+ * Returns 0 on success
+ */
+struct scatterlist *pci_p2pmem_alloc_sgl(struct pci_dev *pdev,
+					 unsigned int *nents, u32 length)
+{
+	struct scatterlist *sg;
+	void *addr;
+
+	sg = kzalloc(sizeof(*sg), GFP_KERNEL);
+	if (!sg)
+		return NULL;
+
+	sg_init_table(sg, 1);
+
+	addr = pci_alloc_p2pmem(pdev, length);
+	if (!addr)
+		goto out_free_sg;
+
+	sg_set_buf(sg, addr, length);
+	*nents = 1;
+	return sg;
+
+out_free_sg:
+	kfree(sg);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(pci_p2pmem_alloc_sgl);
+
+/**
+ * pci_p2pmem_free_sgl - free a scatterlist allocated by pci_p2pmem_alloc_sgl()
+ * @pdev: the device to allocate memory from
+ * @sgl: the allocated scatterlist
+ * @nents: the number of SG entries in the list
+ */
+void pci_p2pmem_free_sgl(struct pci_dev *pdev, struct scatterlist *sgl)
+{
+	struct scatterlist *sg;
+	int count;
+
+	for_each_sg(sgl, sg, INT_MAX, count) {
+		if (!sg)
+			break;
+
+		pci_free_p2pmem(pdev, sg_virt(sg), sg->length);
+	}
+	kfree(sgl);
+}
+EXPORT_SYMBOL_GPL(pci_p2pmem_free_sgl);
+
+/**
+ * pci_p2pmem_publish - publish the peer-to-peer DMA memory for use by
+ *	other devices with pci_p2pmem_find()
+ * @pdev: the device with peer-to-peer DMA memory to publish
+ * @publish: set to true to publish the memory, false to unpublish it
+ *
+ * Published memory can be used by other PCI device drivers for
+ * peer-2-peer DMA operations. Non-published memory is reserved for
+ * exlusive use of the device driver that registers the peer-to-peer
+ * memory.
+ */
+void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
+{
+	if (publish && !pdev->p2pdma)
+		return;
+
+	pdev->p2pdma->p2pmem_published = publish;
+}
+EXPORT_SYMBOL_GPL(pci_p2pmem_publish);
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index f91f9e763557..9553370ebdad 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -53,11 +53,16 @@ struct vmem_altmap {
  * wakeup event whenever a page is unpinned and becomes idle. This
  * wakeup is used to coordinate physical address space management (ex:
  * fs truncate/hole punch) vs pinned pages (ex: device dma).
+ *
+ * MEMORY_DEVICE_PCI_P2PDMA:
+ * Device memory residing in a PCI BAR intended for use with Peer-to-Peer
+ * transactions.
  */
 enum memory_type {
 	MEMORY_DEVICE_PRIVATE = 1,
 	MEMORY_DEVICE_PUBLIC,
 	MEMORY_DEVICE_FS_DAX,
+	MEMORY_DEVICE_PCI_P2PDMA,
 };
 
 /*
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a61ebe8ad4ca..2055df412a77 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -890,6 +890,19 @@ static inline bool is_device_public_page(const struct page *page)
 		page->pgmap->type == MEMORY_DEVICE_PUBLIC;
 }
 
+#ifdef CONFIG_PCI_P2PDMA
+static inline bool is_pci_p2pdma_page(const struct page *page)
+{
+	return is_zone_device_page(page) &&
+		page->pgmap->type == MEMORY_DEVICE_PCI_P2PDMA;
+}
+#else /* CONFIG_PCI_P2PDMA */
+static inline bool is_pci_p2pdma_page(const struct page *page)
+{
+	return false;
+}
+#endif /* CONFIG_PCI_P2PDMA */
+
 #else /* CONFIG_DEV_PAGEMAP_OPS */
 static inline void dev_pagemap_get_ops(void)
 {
@@ -913,6 +926,11 @@ static inline bool is_device_public_page(const struct page *page)
 {
 	return false;
 }
+
+static inline bool is_pci_p2pdma_page(const struct page *page)
+{
+	return false;
+}
 #endif /* CONFIG_DEV_PAGEMAP_OPS */
 
 static inline void get_page(struct page *page)
diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h
new file mode 100644
index 000000000000..7b2b0f547528
--- /dev/null
+++ b/include/linux/pci-p2pdma.h
@@ -0,0 +1,102 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * PCI Peer 2 Peer DMA support.
+ *
+ * Copyright (c) 2016-2018, Logan Gunthorpe
+ * Copyright (c) 2016-2017, Microsemi Corporation
+ * Copyright (c) 2017, Christoph Hellwig
+ * Copyright (c) 2018, Eideticom Inc.
+ *
+ */
+
+#ifndef _LINUX_PCI_P2PDMA_H
+#define _LINUX_PCI_P2PDMA_H
+
+#include <linux/pci.h>
+
+struct block_device;
+struct scatterlist;
+
+#ifdef CONFIG_PCI_P2PDMA
+int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
+		u64 offset);
+int pci_p2pdma_add_client(struct list_head *head, struct device *dev);
+void pci_p2pdma_remove_client(struct list_head *head, struct device *dev);
+void pci_p2pdma_client_list_free(struct list_head *head);
+int pci_p2pdma_distance(struct pci_dev *provider, struct list_head *clients,
+			bool verbose);
+bool pci_p2pdma_assign_provider(struct pci_dev *provider,
+				struct list_head *clients);
+bool pci_has_p2pmem(struct pci_dev *pdev);
+struct pci_dev *pci_p2pmem_find(struct list_head *clients);
+void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size);
+void pci_free_p2pmem(struct pci_dev *pdev, void *addr, size_t size);
+pci_bus_addr_t pci_p2pmem_virt_to_bus(struct pci_dev *pdev, void *addr);
+struct scatterlist *pci_p2pmem_alloc_sgl(struct pci_dev *pdev,
+					 unsigned int *nents, u32 length);
+void pci_p2pmem_free_sgl(struct pci_dev *pdev, struct scatterlist *sgl);
+void pci_p2pmem_publish(struct pci_dev *pdev, bool publish);
+#else /* CONFIG_PCI_P2PDMA */
+static inline int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar,
+		size_t size, u64 offset)
+{
+	return -EOPNOTSUPP;
+}
+static inline int pci_p2pdma_add_client(struct list_head *head,
+		struct device *dev)
+{
+	return 0;
+}
+static inline void pci_p2pdma_remove_client(struct list_head *head,
+		struct device *dev)
+{
+}
+static inline void pci_p2pdma_client_list_free(struct list_head *head)
+{
+}
+static inline int pci_p2pdma_distance(struct pci_dev *provider,
+				      struct list_head *clients,
+				      bool verbose)
+{
+	return -1;
+}
+static inline bool pci_p2pdma_assign_provider(struct pci_dev *provider,
+					      struct list_head *clients)
+{
+	return false;
+}
+static inline bool pci_has_p2pmem(struct pci_dev *pdev)
+{
+	return false;
+}
+static inline struct pci_dev *pci_p2pmem_find(struct list_head *clients)
+{
+	return NULL;
+}
+static inline void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size)
+{
+	return NULL;
+}
+static inline void pci_free_p2pmem(struct pci_dev *pdev, void *addr,
+		size_t size)
+{
+}
+static inline pci_bus_addr_t pci_p2pmem_virt_to_bus(struct pci_dev *pdev,
+						    void *addr)
+{
+	return 0;
+}
+static inline struct scatterlist *pci_p2pmem_alloc_sgl(struct pci_dev *pdev,
+		unsigned int *nents, u32 length)
+{
+	return NULL;
+}
+static inline void pci_p2pmem_free_sgl(struct pci_dev *pdev,
+		struct scatterlist *sgl)
+{
+}
+static inline void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
+{
+}
+#endif /* CONFIG_PCI_P2PDMA */
+#endif /* _LINUX_PCI_P2P_H */
diff --git a/include/linux/pci.h b/include/linux/pci.h
index e72ca8dd6241..5d95dbf21f4a 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -281,6 +281,7 @@ struct pcie_link_state;
 struct pci_vpd;
 struct pci_sriov;
 struct pci_ats;
+struct pci_p2pdma;
 
 /* The pci_dev structure describes PCI devices */
 struct pci_dev {
@@ -438,6 +439,9 @@ struct pci_dev {
 #endif
 #ifdef CONFIG_PCI_PASID
 	u16		pasid_features;
+#endif
+#ifdef CONFIG_PCI_P2PDMA
+	struct pci_p2pdma *p2pdma;
 #endif
 	phys_addr_t	rom;		/* Physical address if not from BAR */
 	size_t		romlen;		/* Length if not from BAR */
-- 
2.19.0

[PATCH v6 02/13] PCI/P2PDMA: Add sysfs group to display p2pmem stats

[Logan Gunthorpe]

Add a sysfs group to display statistics about P2P memory that is
registered in each PCI device.

Attributes in the group display the total amount of P2P memory, the
amount available and whether it is published or not.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
 Documentation/ABI/testing/sysfs-bus-pci | 25 ++++++++++++
 drivers/pci/p2pdma.c                    | 54 +++++++++++++++++++++++++
 2 files changed, 79 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index 44d4b2be92fd..044812c816d0 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci
+++ b/Documentation/ABI/testing/sysfs-bus-pci
@@ -323,3 +323,28 @@ Description:
 
 		This is similar to /sys/bus/pci/drivers_autoprobe, but
 		affects only the VFs associated with a specific PF.
+
+What:		/sys/bus/pci/devices/.../p2pmem/available
+Date:		November 2017
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:
+		If the device has any Peer-to-Peer memory registered, this
+	        file contains the amount of memory that has not been
+		allocated (in decimal).
+
+What:		/sys/bus/pci/devices/.../p2pmem/size
+Date:		November 2017
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:
+		If the device has any Peer-to-Peer memory registered, this
+	        file contains the total amount of memory that the device
+		provides (in decimal).
+
+What:		/sys/bus/pci/devices/.../p2pmem/published
+Date:		November 2017
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:
+		If the device has any Peer-to-Peer memory registered, this
+	        file contains a '1' if the memory has been published for
+		use inside the kernel or a '0' if it is only intended
+		for use within the driver that published it.
diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 88aaec5351cd..67c1daf1189e 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -25,6 +25,54 @@ struct pci_p2pdma {
 	bool p2pmem_published;
 };
 
+static ssize_t size_show(struct device *dev, struct device_attribute *attr,
+			 char *buf)
+{
+	struct pci_dev *pdev = to_pci_dev(dev);
+	size_t size = 0;
+
+	if (pdev->p2pdma->pool)
+		size = gen_pool_size(pdev->p2pdma->pool);
+
+	return snprintf(buf, PAGE_SIZE, "%zd\n", size);
+}
+static DEVICE_ATTR_RO(size);
+
+static ssize_t available_show(struct device *dev, struct device_attribute *attr,
+			      char *buf)
+{
+	struct pci_dev *pdev = to_pci_dev(dev);
+	size_t avail = 0;
+
+	if (pdev->p2pdma->pool)
+		avail = gen_pool_avail(pdev->p2pdma->pool);
+
+	return snprintf(buf, PAGE_SIZE, "%zd\n", avail);
+}
+static DEVICE_ATTR_RO(available);
+
+static ssize_t published_show(struct device *dev, struct device_attribute *attr,
+			      char *buf)
+{
+	struct pci_dev *pdev = to_pci_dev(dev);
+
+	return snprintf(buf, PAGE_SIZE, "%d\n",
+			pdev->p2pdma->p2pmem_published);
+}
+static DEVICE_ATTR_RO(published);
+
+static struct attribute *p2pmem_attrs[] = {
+	&dev_attr_size.attr,
+	&dev_attr_available.attr,
+	&dev_attr_published.attr,
+	NULL,
+};
+
+static const struct attribute_group p2pmem_group = {
+	.attrs = p2pmem_attrs,
+	.name = "p2pmem",
+};
+
 static void pci_p2pdma_percpu_release(struct percpu_ref *ref)
 {
 	struct pci_p2pdma *p2p =
@@ -54,6 +102,7 @@ static void pci_p2pdma_release(void *data)
 	percpu_ref_exit(&pdev->p2pdma->devmap_ref);
 
 	gen_pool_destroy(pdev->p2pdma->pool);
+	sysfs_remove_group(&pdev->dev.kobj, &p2pmem_group);
 	pdev->p2pdma = NULL;
 }
 
@@ -84,9 +133,14 @@ static int pci_p2pdma_setup(struct pci_dev *pdev)
 
 	pdev->p2pdma = p2p;
 
+	error = sysfs_create_group(&pdev->dev.kobj, &p2pmem_group);
+	if (error)
+		goto out_pool_destroy;
+
 	return 0;
 
 out_pool_destroy:
+	pdev->p2pdma = NULL;
 	gen_pool_destroy(p2p->pool);
 out:
 	devm_kfree(&pdev->dev, p2p);
-- 
2.19.0

[PATCH v6 03/13] PCI/P2PDMA: Add PCI p2pmem DMA mappings to adjust the bus offset

[Logan Gunthorpe]

The DMA address used when mapping PCI P2P memory must be the PCI bus
address. Thus, introduce pci_p2pmem_map_sg() to map the correct
addresses when using P2P memory. Memory mapped in this way does not
need to be unmapped.

For this, we assume that an SGL passed to these functions contain all
P2P memory or no P2P memory.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
 drivers/pci/p2pdma.c       | 43 ++++++++++++++++++++++++++++++++++++++
 include/linux/memremap.h   |  1 +
 include/linux/pci-p2pdma.h |  7 +++++++
 3 files changed, 51 insertions(+)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 67c1daf1189e..29bd40a87768 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -191,6 +191,8 @@ int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
 	pgmap->res.flags = pci_resource_flags(pdev, bar);
 	pgmap->ref = &pdev->p2pdma->devmap_ref;
 	pgmap->type = MEMORY_DEVICE_PCI_P2PDMA;
+	pgmap->pci_p2pdma_bus_offset = pci_bus_address(pdev, bar) -
+		pci_resource_start(pdev, bar);
 
 	addr = devm_memremap_pages(&pdev->dev, pgmap);
 	if (IS_ERR(addr)) {
@@ -813,3 +815,44 @@ void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
 	pdev->p2pdma->p2pmem_published = publish;
 }
 EXPORT_SYMBOL_GPL(pci_p2pmem_publish);
+
+/**
+ * pci_p2pdma_map_sg - map a PCI peer-to-peer scatterlist for DMA
+ * @dev: device doing the DMA request
+ * @sg: scatter list to map
+ * @nents: elements in the scatterlist
+ * @dir: DMA direction
+ *
+ * Scatterlists mapped with this function should not be unmapped in any way.
+ *
+ * Returns the number of SG entries mapped or 0 on error.
+ */
+int pci_p2pdma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
+		      enum dma_data_direction dir)
+{
+	struct dev_pagemap *pgmap;
+	struct scatterlist *s;
+	phys_addr_t paddr;
+	int i;
+
+	/*
+	 * p2pdma mappings are not compatible with devices that use
+	 * dma_virt_ops. If the upper layers do the right thing
+	 * this should never happen because it will be prevented
+	 * by the check in pci_p2pdma_add_client()
+	 */
+	if (WARN_ON_ONCE(IS_ENABLED(CONFIG_DMA_VIRT_OPS) &&
+			 dev->dma_ops == &dma_virt_ops))
+		return 0;
+
+	for_each_sg(sg, s, nents, i) {
+		pgmap = sg_page(s)->pgmap;
+		paddr = sg_phys(s);
+
+		s->dma_address = paddr - pgmap->pci_p2pdma_bus_offset;
+		sg_dma_len(s) = s->length;
+	}
+
+	return nents;
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_map_sg);
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 9553370ebdad..0ac69ddf5fc4 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -125,6 +125,7 @@ struct dev_pagemap {
 	struct device *dev;
 	void *data;
 	enum memory_type type;
+	u64 pci_p2pdma_bus_offset;
 };
 
 #ifdef CONFIG_ZONE_DEVICE
diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h
index 7b2b0f547528..2f03dbbf5af6 100644
--- a/include/linux/pci-p2pdma.h
+++ b/include/linux/pci-p2pdma.h
@@ -36,6 +36,8 @@ struct scatterlist *pci_p2pmem_alloc_sgl(struct pci_dev *pdev,
 					 unsigned int *nents, u32 length);
 void pci_p2pmem_free_sgl(struct pci_dev *pdev, struct scatterlist *sgl);
 void pci_p2pmem_publish(struct pci_dev *pdev, bool publish);
+int pci_p2pdma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
+		      enum dma_data_direction dir);
 #else /* CONFIG_PCI_P2PDMA */
 static inline int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar,
 		size_t size, u64 offset)
@@ -98,5 +100,10 @@ static inline void pci_p2pmem_free_sgl(struct pci_dev *pdev,
 static inline void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
 {
 }
+static inline int pci_p2pdma_map_sg(struct device *dev,
+		struct scatterlist *sg, int nents, enum dma_data_direction dir)
+{
+	return 0;
+}
 #endif /* CONFIG_PCI_P2PDMA */
 #endif /* _LINUX_PCI_P2P_H */
-- 
2.19.0

[PATCH v6 04/13] PCI/P2PDMA: Introduce configfs/sysfs enable attribute helpers

[Logan Gunthorpe]

Users of the P2PDMA infrastructure will typically need a way for
the user to tell the kernel to use P2P resources. Typically
this will be a simple on/off boolean operation but sometimes
it may be desirable for the user to specify the exact device to
use for the P2P operation.

Add new helpers for attributes which take a boolean or a PCI device.
Any boolean, or the word 'auto' turn P2P on or off. Specifying a full
PCI device name/BDF will select the specific device.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
 drivers/pci/p2pdma.c       | 83 ++++++++++++++++++++++++++++++++++++++
 include/linux/pci-p2pdma.h | 15 +++++++
 2 files changed, 98 insertions(+)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 29bd40a87768..3da848f3fe72 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -9,6 +9,7 @@
  */
 
 #define pr_fmt(fmt) "pci-p2pdma: " fmt
+#include <linux/ctype.h>
 #include <linux/pci-p2pdma.h>
 #include <linux/module.h>
 #include <linux/slab.h>
@@ -856,3 +857,85 @@ int pci_p2pdma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
 	return nents;
 }
 EXPORT_SYMBOL_GPL(pci_p2pdma_map_sg);
+
+/**
+ * pci_p2pdma_enable_store - parse a configfs/sysfs attribute store
+ *		to enable p2pdma
+ * @page: contents of the value to be stored
+ * @p2p_dev: returns the PCI device that was selected to be used
+ *		(if 'auto', 'none or a boolean isn't the store value)
+ * @use_p2pdma: returns whether to enable p2pdma or not
+ *
+ * Parses an attribute value to decide whether to enable p2pdma.
+ * The value can select a PCI device (using it's full BDF device
+ * name), a boolean, or 'auto'. 'auto' and a true boolean value
+ * have the same meaning. A false value disables p2pdma and
+ * a PCI device enables it to use a specific device as the
+ * backing provider.
+ *
+ * pci_p2pdma_enable_show() should be used as the show operation for
+ * the attribute.
+ *
+ * Returns 0 on success
+ */
+int pci_p2pdma_enable_store(const char *page, struct pci_dev **p2p_dev,
+			    bool *use_p2pdma)
+{
+	struct device *dev;
+
+	dev = bus_find_device_by_name(&pci_bus_type, NULL, page);
+	if (dev) {
+		*use_p2pdma = true;
+		*p2p_dev = to_pci_dev(dev);
+
+		if (!pci_has_p2pmem(*p2p_dev)) {
+			pr_err("PCI device has no peer-to-peer memory: %s\n",
+			       page);
+			pci_dev_put(*p2p_dev);
+			return -ENODEV;
+		}
+
+		return 0;
+	} else if (sysfs_streq(page, "auto")) {
+		*use_p2pdma = true;
+		return 0;
+	} else if ((page[0] == '0' || page[0] == '1') && !iscntrl(page[1])) {
+		/*
+		 * If the user enters a PCI device that  doesn't exist
+		 * like "0000:01:00.1", we don't want strtobool to think
+		 * it's a '0' when it's clearly not what the user wanted.
+		 * So we require 0's and 1's to be exactly one character.
+		 */
+	} else if (!strtobool(page, use_p2pdma)) {
+		return 0;
+	}
+
+	pr_err("No such PCI device: %.*s\n", (int)strcspn(page, "\n"), page);
+	return -ENODEV;
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_enable_store);
+
+/**
+ * pci_p2pdma_enable_show - show a configfs/sysfs attribute indicating
+ *		whether p2pdma is enabled
+ * @page: contents of the stored value
+ * @p2p_dev: the selected p2p device (NULL if no device is selected)
+ * @use_p2pdma: whether p2pdme has been enabled
+ *
+ * Attributes that use pci_p2pdma_enable_store() should use this function
+ * to show the value of the attribute.
+ *
+ * Returns 0 on success
+ */
+ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
+			       bool use_p2pdma)
+{
+	if (!use_p2pdma)
+		return sprintf(page, "none\n");
+
+	if (!p2p_dev)
+		return sprintf(page, "auto\n");
+
+	return sprintf(page, "%s\n", pci_name(p2p_dev));
+}
+EXPORT_SYMBOL_GPL(pci_p2pdma_enable_show);
diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h
index 2f03dbbf5af6..377de4d73767 100644
--- a/include/linux/pci-p2pdma.h
+++ b/include/linux/pci-p2pdma.h
@@ -38,6 +38,10 @@ void pci_p2pmem_free_sgl(struct pci_dev *pdev, struct scatterlist *sgl);
 void pci_p2pmem_publish(struct pci_dev *pdev, bool publish);
 int pci_p2pdma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
 		      enum dma_data_direction dir);
+int pci_p2pdma_enable_store(const char *page, struct pci_dev **p2p_dev,
+			    bool *use_p2pdma);
+ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
+			       bool use_p2pdma);
 #else /* CONFIG_PCI_P2PDMA */
 static inline int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar,
 		size_t size, u64 offset)
@@ -105,5 +109,16 @@ static inline int pci_p2pdma_map_sg(struct device *dev,
 {
 	return 0;
 }
+static inline int pci_p2pdma_enable_store(const char *page,
+		struct pci_dev **p2p_dev, bool *use_p2pdma)
+{
+	*use_p2pdma = false;
+	return 0;
+}
+static inline ssize_t pci_p2pdma_enable_show(char *page,
+		struct pci_dev *p2p_dev, bool use_p2pdma)
+{
+	return sprintf(page, "none\n");
+}
 #endif /* CONFIG_PCI_P2PDMA */
 #endif /* _LINUX_PCI_P2P_H */
-- 
2.19.0

[PATCH v6 05/13] docs-rst: Add a new directory for PCI documentation

[Logan Gunthorpe]

Add a new directory in the driver API guide for PCI specific
documentation.

This is in preparation for adding a new PCI P2P DMA driver writers
guide which will go in this directory.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Vinod Koul <vinod.koul@intel.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: Thierry Reding <treding@nvidia.com>
Cc: Sanyog Kale <sanyog.r.kale@intel.com>
Cc: Sagar Dharia <sdharia@codeaurora.org>
---
 Documentation/driver-api/index.rst         |  2 +-
 Documentation/driver-api/pci/index.rst     | 20 ++++++++++++++++++++
 Documentation/driver-api/{ => pci}/pci.rst |  0
 3 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/driver-api/pci/index.rst
 rename Documentation/driver-api/{ => pci}/pci.rst (100%)

diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst
index 6d9f2f9fe20e..e9e7d24169cf 100644
--- a/Documentation/driver-api/index.rst
+++ b/Documentation/driver-api/index.rst
@@ -29,7 +29,7 @@ available subsections can be seen below.
    iio/index
    input
    usb/index
-   pci
+   pci/index
    spi
    i2c
    hsi
diff --git a/Documentation/driver-api/pci/index.rst b/Documentation/driver-api/pci/index.rst
new file mode 100644
index 000000000000..eaf20b24bf7d
--- /dev/null
+++ b/Documentation/driver-api/pci/index.rst
@@ -0,0 +1,20 @@
+.. SPDX-License-Identifier: GPL-2.0
+============================================
+The Linux PCI driver implementer's API guide
+============================================
+
+.. class:: toc-title
+
+	   Table of contents
+
+.. toctree::
+   :maxdepth: 2
+
+   pci
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`
diff --git a/Documentation/driver-api/pci.rst b/Documentation/driver-api/pci/pci.rst
similarity index 100%
rename from Documentation/driver-api/pci.rst
rename to Documentation/driver-api/pci/pci.rst
-- 
2.19.0

[PATCH v6 06/13] PCI/P2PDMA: Add P2P DMA driver writer's documentation

[Logan Gunthorpe]

Add a restructured text file describing how to write drivers
with support for P2P DMA transactions. The document describes
how to use the APIs that were added in the previous few
commits.

Also adds an index for the PCI documentation tree even though this
is the only PCI document that has been converted to restructured text
at this time.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Cc: Jonathan Corbet <corbet@lwn.net>
---
 Documentation/driver-api/pci/index.rst  |   1 +
 Documentation/driver-api/pci/p2pdma.rst | 170 ++++++++++++++++++++++++
 2 files changed, 171 insertions(+)
 create mode 100644 Documentation/driver-api/pci/p2pdma.rst

diff --git a/Documentation/driver-api/pci/index.rst b/Documentation/driver-api/pci/index.rst
index eaf20b24bf7d..ecc7416c523b 100644
--- a/Documentation/driver-api/pci/index.rst
+++ b/Documentation/driver-api/pci/index.rst
@@ -11,6 +11,7 @@ The Linux PCI driver implementer's API guide
    :maxdepth: 2
 
    pci
+   p2pdma
 
 .. only::  subproject and html
 
diff --git a/Documentation/driver-api/pci/p2pdma.rst b/Documentation/driver-api/pci/p2pdma.rst
new file mode 100644
index 000000000000..38cfd9295a72
--- /dev/null
+++ b/Documentation/driver-api/pci/p2pdma.rst
@@ -0,0 +1,170 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+============================
+PCI Peer-to-Peer DMA Support
+============================
+
+The PCI bus has pretty decent support for performing DMA transfers
+between two devices on the bus. This type of transaction is henceforth
+called Peer-to-Peer (or P2P). However, there are a number of issues that
+make P2P transactions tricky to do in a perfectly safe way.
+
+One of the biggest issues is that PCI doesn't require forwarding
+transactions between hierarchy domains, and in PCIe, each Root Port
+defines a separate hierarchy domain. To make things worse, there is no
+simple way to determine if a given Root Complex supports this or not.
+(See PCIe r4.0, sec 1.3.1). Therefore, as of this writing, the kernel
+only supports doing P2P when the endpoints involved are all behind the
+same PCI bridge, as such devices are all in the same PCI hierarchy
+domain, and the spec guarantees that all transactions within the
+hierarchy will be routable, but it does not require routing
+between hierarchies.
+
+The second issue is that to make use of existing interfaces in Linux,
+memory that is used for P2P transactions needs to be backed by struct
+pages. However, PCI BARs are not typically cache coherent so there are
+a few corner case gotchas with these pages so developers need to
+be careful about what they do with them.
+
+
+Driver Writer's Guide
+=====================
+
+In a given P2P implementation there may be three or more different
+types of kernel drivers in play:
+
+* Provider - A driver which provides or publishes P2P resources like
+  memory or doorbell registers to other drivers.
+* Client - A driver which makes use of a resource by setting up a
+  DMA transaction to or from it.
+* Orchestrator - A driver which orchestrates the flow of data between
+  clients and providers.
+
+In many cases there could be overlap between these three types (i.e.,
+it may be typical for a driver to be both a provider and a client).
+
+For example, in the NVMe Target Copy Offload implementation:
+
+* The NVMe PCI driver is both a client, provider and orchestrator
+  in that it exposes any CMB (Controller Memory Buffer) as a P2P memory
+  resource (provider), it accepts P2P memory pages as buffers in requests
+  to be used directly (client) and it can also make use the CMB as
+  submission queue entries.
+* The RDMA driver is a client in this arrangement so that an RNIC
+  can DMA directly to the memory exposed by the NVMe device.
+* The NVMe Target driver (nvmet) can orchestrate the data from the RNIC
+  to the P2P memory (CMB) and then to the NVMe device (and vice versa).
+
+This is currently the only arrangement supported by the kernel but
+one could imagine slight tweaks to this that would allow for the same
+functionality. For example, if a specific RNIC added a BAR with some
+memory behind it, its driver could add support as a P2P provider and
+then the NVMe Target could use the RNIC's memory instead of the CMB
+in cases where the NVMe cards in use do not have CMB support.
+
+
+Provider Drivers
+----------------
+
+A provider simply needs to register a BAR (or a portion of a BAR)
+as a P2P DMA resource using :c:func:`pci_p2pdma_add_resource()`.
+This will register struct pages for all the specified memory.
+
+After that it may optionally publish all of its resources as
+P2P memory using :c:func:`pci_p2pmem_publish()`. This will allow
+any orchestrator drivers to find and use the memory. When marked in
+this way, the resource must be regular memory with no side effects.
+
+For the time being this is fairly rudimentary in that all resources
+are typically going to be P2P memory. Future work will likely expand
+this to include other types of resources like doorbells.
+
+
+Client Drivers
+--------------
+
+A client driver typically only has to conditionally change its DMA map
+routine to use the mapping function :c:func:`pci_p2pdma_map_sg()` instead
+of the usual :c:func:`dma_map_sg()` function. Memory mapped in this
+way does not need to be unmapped.
+
+The client may also, optionally, make use of
+:c:func:`is_pci_p2pdma_page()` to determine when to use the P2P mapping
+functions and when to use the regular mapping functions. In some
+situations, it may be more appropriate to use a flag to indicate a
+given request is P2P memory and map appropriately (for example the
+block layer uses a flag to keep P2P memory out of queues that do not
+have P2P client support). It is important to ensure that struct pages that
+back P2P memory stay out of code that does not have support for them.
+
+
+Orchestrator Drivers
+--------------------
+
+The first task an orchestrator driver must do is compile a list of
+all client devices that will be involved in a given transaction. For
+example, the NVMe Target driver creates a list including all NVMe
+devices and the RNIC in use. The list is stored as an anonymous struct
+list_head which must be initialized with the usual INIT_LIST_HEAD.
+The following functions may then be used to add to, remove from and free
+the list of clients with the functions :c:func:`pci_p2pdma_add_client()`,
+:c:func:`pci_p2pdma_remove_client()` and
+:c:func:`pci_p2pdma_client_list_free()`.
+
+With the client list in hand, the orchestrator may then call
+:c:func:`pci_p2pmem_find()` to obtain a published P2P memory provider
+that is supported (behind the same root port) as all the clients. If more
+than one provider is supported, the one nearest to all the clients will
+be chosen first. If there are more than one provider is an equal distance
+away, the one returned will be chosen at random. This function returns the PCI
+device to use for the provider with a reference taken and therefore
+when it's no longer needed it should be returned with pci_dev_put().
+
+Alternatively, if the orchestrator knows (via some other means)
+which provider it wants to use it may use :c:func:`pci_has_p2pmem()`
+to determine if it has P2P memory and :c:func:`pci_p2pdma_distance()`
+to determine the cumulative distance between it and a potential
+list of clients.
+
+With a supported provider in hand, the driver can then call
+:c:func:`pci_p2pdma_assign_provider()` to assign the provider
+to the client list. This function returns false if any of the
+clients are unsupported by the provider.
+
+Once a provider is assigned to a client list via either
+:c:func:`pci_p2pmem_find()` or :c:func:`pci_p2pdma_assign_provider()`,
+the list is permanently bound to the provider such that any new clients
+added to the list must be supported by the already selected provider.
+If they are not supported, :c:func:`pci_p2pdma_add_client()` will return
+an error. In this way, orchestrators are free to add and remove devices
+without having to recheck support or tear down existing transfers to
+change P2P providers.
+
+Once a provider is selected, the orchestrator can then use
+:c:func:`pci_alloc_p2pmem()` and :c:func:`pci_free_p2pmem()` to
+allocate P2P memory from the provider. :c:func:`pci_p2pmem_alloc_sgl()`
+and :c:func:`pci_p2pmem_free_sgl()` are convenience functions for
+allocating scatter-gather lists with P2P memory.
+
+Struct Page Caveats
+-------------------
+
+Driver writers should be very careful about not passing these special
+struct pages to code that isn't prepared for it. At this time, the kernel
+interfaces do not have any checks for ensuring this. This obviously
+precludes passing these pages to userspace.
+
+P2P memory is also technically IO memory but should never have any side
+effects behind it. Thus, the order of loads and stores should not be important
+and ioreadX(), iowriteX() and friends should not be necessary.
+However, as the memory is not cache coherent, if access ever needs to
+be protected by a spinlock then :c:func:`mmiowb()` must be used before
+unlocking the lock. (See ACQUIRES VS I/O ACCESSES in
+Documentation/memory-barriers.txt)
+
+
+P2P DMA Support Library
+=====================
+
+.. kernel-doc:: drivers/pci/p2pdma.c
+   :export:
-- 
2.19.0

[PATCH v6 07/13] block: Add PCI P2P flag for request queue and check support for requests

[Logan Gunthorpe]

QUEUE_FLAG_PCI_P2P is introduced meaning a driver's request queue
supports targeting P2P memory.

When a request is submitted we check if PCI P2PDMA memory is assigned
to the first page in the bio. If it is, we ensure the queue it's
submitted to supports it, and enforce REQ_NOMERGE.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
 include/linux/blkdev.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index d6869e0e2b64..7bf80ca802e1 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -699,6 +699,7 @@ struct request_queue {
 #define QUEUE_FLAG_SCSI_PASSTHROUGH 27	/* queue supports SCSI commands */
 #define QUEUE_FLAG_QUIESCED    28	/* queue has been quiesced */
 #define QUEUE_FLAG_PREEMPT_ONLY	29	/* only process REQ_PREEMPT requests */
+#define QUEUE_FLAG_PCI_P2PDMA  30	/* device supports pci p2p requests */
 
 #define QUEUE_FLAG_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\
 				 (1 << QUEUE_FLAG_SAME_COMP)	|	\
@@ -731,6 +732,8 @@ bool blk_queue_flag_test_and_clear(unsigned int flag, struct request_queue *q);
 #define blk_queue_dax(q)	test_bit(QUEUE_FLAG_DAX, &(q)->queue_flags)
 #define blk_queue_scsi_passthrough(q)	\
 	test_bit(QUEUE_FLAG_SCSI_PASSTHROUGH, &(q)->queue_flags)
+#define blk_queue_pci_p2pdma(q)	\
+	test_bit(QUEUE_FLAG_PCI_P2PDMA, &(q)->queue_flags)
 
 #define blk_noretry_request(rq) \
 	((rq)->cmd_flags & (REQ_FAILFAST_DEV|REQ_FAILFAST_TRANSPORT| \
-- 
2.19.0

[PATCH v6 08/13] IB/core: Ensure we map P2P memory correctly in rdma_rw_ctx_[init|destroy]()

[Logan Gunthorpe]

In order to use PCI P2P memory the pci_p2pmem_map_sg() function must be
called to map the correct PCI bus address.

To do this, check the first page in the scatter list to see if it is P2P
memory or not. At the moment, scatter lists that contain P2P memory must
be homogeneous so if the first page is P2P the entire SGL should be P2P.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
---
 drivers/infiniband/core/rw.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/core/rw.c b/drivers/infiniband/core/rw.c
index 683e6d11a564..d22c4a2ebac6 100644
--- a/drivers/infiniband/core/rw.c
+++ b/drivers/infiniband/core/rw.c
@@ -12,6 +12,7 @@
  */
 #include <linux/moduleparam.h>
 #include <linux/slab.h>
+#include <linux/pci-p2pdma.h>
 #include <rdma/mr_pool.h>
 #include <rdma/rw.h>
 
@@ -280,7 +281,11 @@ int rdma_rw_ctx_init(struct rdma_rw_ctx *ctx, struct ib_qp *qp, u8 port_num,
 	struct ib_device *dev = qp->pd->device;
 	int ret;
 
-	ret = ib_dma_map_sg(dev, sg, sg_cnt, dir);
+	if (is_pci_p2pdma_page(sg_page(sg)))
+		ret = pci_p2pdma_map_sg(dev->dma_device, sg, sg_cnt, dir);
+	else
+		ret = ib_dma_map_sg(dev, sg, sg_cnt, dir);
+
 	if (!ret)
 		return -ENOMEM;
 	sg_cnt = ret;
@@ -602,7 +607,9 @@ void rdma_rw_ctx_destroy(struct rdma_rw_ctx *ctx, struct ib_qp *qp, u8 port_num,
 		break;
 	}
 
-	ib_dma_unmap_sg(qp->pd->device, sg, sg_cnt, dir);
+	/* P2PDMA contexts do not need to be unmapped */
+	if (!is_pci_p2pdma_page(sg_page(sg)))
+		ib_dma_unmap_sg(qp->pd->device, sg, sg_cnt, dir);
 }
 EXPORT_SYMBOL(rdma_rw_ctx_destroy);
 
-- 
2.19.0

[PATCH v6 09/13] nvme-pci: Use PCI p2pmem subsystem to manage the CMB

[Logan Gunthorpe]

Register the CMB buffer as p2pmem and use the appropriate allocation
functions to create and destroy the IO submission queues.

If the CMB supports WDS and RDS, publish it for use as P2P memory
by other devices.

Kernels without CONFIG_PCI_P2PDMA will also no longer support NVMe CMB.
However, seeing the main use-cases for the CMB is P2P operations,
this seems like a reasonable dependency.

We drop the __iomem safety on the buffer seeing that, by convention, it's
safe to directly access memory mapped by memremap()/devm_memremap_pages().
Architectures where this is not safe will not be supported by memremap()
and therefore will not be support PCI P2P and have no support for CMB.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
 drivers/nvme/host/pci.c | 80 +++++++++++++++++++++++------------------
 1 file changed, 45 insertions(+), 35 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index d668682f91df..f434706a04e8 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -30,6 +30,7 @@
 #include <linux/types.h>
 #include <linux/io-64-nonatomic-lo-hi.h>
 #include <linux/sed-opal.h>
+#include <linux/pci-p2pdma.h>
 
 #include "nvme.h"
 
@@ -99,9 +100,8 @@ struct nvme_dev {
 	struct work_struct remove_work;
 	struct mutex shutdown_lock;
 	bool subsystem;
-	void __iomem *cmb;
-	pci_bus_addr_t cmb_bus_addr;
 	u64 cmb_size;
+	bool cmb_use_sqes;
 	u32 cmbsz;
 	u32 cmbloc;
 	struct nvme_ctrl ctrl;
@@ -158,7 +158,7 @@ struct nvme_queue {
 	struct nvme_dev *dev;
 	spinlock_t sq_lock;
 	struct nvme_command *sq_cmds;
-	struct nvme_command __iomem *sq_cmds_io;
+	bool sq_cmds_is_io;
 	spinlock_t cq_lock ____cacheline_aligned_in_smp;
 	volatile struct nvme_completion *cqes;
 	struct blk_mq_tags **tags;
@@ -447,11 +447,8 @@ static int nvme_pci_map_queues(struct blk_mq_tag_set *set)
 static void nvme_submit_cmd(struct nvme_queue *nvmeq, struct nvme_command *cmd)
 {
 	spin_lock(&nvmeq->sq_lock);
-	if (nvmeq->sq_cmds_io)
-		memcpy_toio(&nvmeq->sq_cmds_io[nvmeq->sq_tail], cmd,
-				sizeof(*cmd));
-	else
-		memcpy(&nvmeq->sq_cmds[nvmeq->sq_tail], cmd, sizeof(*cmd));
+
+	memcpy(&nvmeq->sq_cmds[nvmeq->sq_tail], cmd, sizeof(*cmd));
 
 	if (++nvmeq->sq_tail == nvmeq->q_depth)
 		nvmeq->sq_tail = 0;
@@ -1232,9 +1229,18 @@ static void nvme_free_queue(struct nvme_queue *nvmeq)
 {
 	dma_free_coherent(nvmeq->q_dmadev, CQ_SIZE(nvmeq->q_depth),
 				(void *)nvmeq->cqes, nvmeq->cq_dma_addr);
-	if (nvmeq->sq_cmds)
-		dma_free_coherent(nvmeq->q_dmadev, SQ_SIZE(nvmeq->q_depth),
-					nvmeq->sq_cmds, nvmeq->sq_dma_addr);
+
+	if (nvmeq->sq_cmds) {
+		if (nvmeq->sq_cmds_is_io)
+			pci_free_p2pmem(to_pci_dev(nvmeq->q_dmadev),
+					nvmeq->sq_cmds,
+					SQ_SIZE(nvmeq->q_depth));
+		else
+			dma_free_coherent(nvmeq->q_dmadev,
+					  SQ_SIZE(nvmeq->q_depth),
+					  nvmeq->sq_cmds,
+					  nvmeq->sq_dma_addr);
+	}
 }
 
 static void nvme_free_queues(struct nvme_dev *dev, int lowest)
@@ -1323,12 +1329,21 @@ static int nvme_cmb_qdepth(struct nvme_dev *dev, int nr_io_queues,
 static int nvme_alloc_sq_cmds(struct nvme_dev *dev, struct nvme_queue *nvmeq,
 				int qid, int depth)
 {
-	/* CMB SQEs will be mapped before creation */
-	if (qid && dev->cmb && use_cmb_sqes && (dev->cmbsz & NVME_CMBSZ_SQS))
-		return 0;
+	struct pci_dev *pdev = to_pci_dev(dev->dev);
+
+	if (qid && dev->cmb_use_sqes && (dev->cmbsz & NVME_CMBSZ_SQS)) {
+		nvmeq->sq_cmds = pci_alloc_p2pmem(pdev, SQ_SIZE(depth));
+		nvmeq->sq_dma_addr = pci_p2pmem_virt_to_bus(pdev,
+						nvmeq->sq_cmds);
+		nvmeq->sq_cmds_is_io = true;
+	}
+
+	if (!nvmeq->sq_cmds) {
+		nvmeq->sq_cmds = dma_alloc_coherent(dev->dev, SQ_SIZE(depth),
+					&nvmeq->sq_dma_addr, GFP_KERNEL);
+		nvmeq->sq_cmds_is_io = false;
+	}
 
-	nvmeq->sq_cmds = dma_alloc_coherent(dev->dev, SQ_SIZE(depth),
-					    &nvmeq->sq_dma_addr, GFP_KERNEL);
 	if (!nvmeq->sq_cmds)
 		return -ENOMEM;
 	return 0;
@@ -1405,13 +1420,6 @@ static int nvme_create_queue(struct nvme_queue *nvmeq, int qid)
 	int result;
 	s16 vector;
 
-	if (dev->cmb && use_cmb_sqes && (dev->cmbsz & NVME_CMBSZ_SQS)) {
-		unsigned offset = (qid - 1) * roundup(SQ_SIZE(nvmeq->q_depth),
-						      dev->ctrl.page_size);
-		nvmeq->sq_dma_addr = dev->cmb_bus_addr + offset;
-		nvmeq->sq_cmds_io = dev->cmb + offset;
-	}
-
 	/*
 	 * A queue's vector matches the queue identifier unless the controller
 	 * has only one vector available.
@@ -1652,9 +1660,6 @@ static void nvme_map_cmb(struct nvme_dev *dev)
 		return;
 	dev->cmbloc = readl(dev->bar + NVME_REG_CMBLOC);
 
-	if (!use_cmb_sqes)
-		return;
-
 	size = nvme_cmb_size_unit(dev) * nvme_cmb_size(dev);
 	offset = nvme_cmb_size_unit(dev) * NVME_CMB_OFST(dev->cmbloc);
 	bar = NVME_CMB_BIR(dev->cmbloc);
@@ -1671,11 +1676,18 @@ static void nvme_map_cmb(struct nvme_dev *dev)
 	if (size > bar_size - offset)
 		size = bar_size - offset;
 
-	dev->cmb = ioremap_wc(pci_resource_start(pdev, bar) + offset, size);
-	if (!dev->cmb)
+	if (pci_p2pdma_add_resource(pdev, bar, size, offset)) {
+		dev_warn(dev->ctrl.device,
+			 "failed to register the CMB\n");
 		return;
-	dev->cmb_bus_addr = pci_bus_address(pdev, bar) + offset;
+	}
+
 	dev->cmb_size = size;
+	dev->cmb_use_sqes = use_cmb_sqes && (dev->cmbsz & NVME_CMBSZ_SQS);
+
+	if ((dev->cmbsz & (NVME_CMBSZ_WDS | NVME_CMBSZ_RDS)) ==
+			(NVME_CMBSZ_WDS | NVME_CMBSZ_RDS))
+		pci_p2pmem_publish(pdev, true);
 
 	if (sysfs_add_file_to_group(&dev->ctrl.device->kobj,
 				    &dev_attr_cmb.attr, NULL))
@@ -1685,12 +1697,10 @@ static void nvme_map_cmb(struct nvme_dev *dev)
 
 static inline void nvme_release_cmb(struct nvme_dev *dev)
 {
-	if (dev->cmb) {
-		iounmap(dev->cmb);
-		dev->cmb = NULL;
+	if (dev->cmb_size) {
 		sysfs_remove_file_from_group(&dev->ctrl.device->kobj,
 					     &dev_attr_cmb.attr, NULL);
-		dev->cmbsz = 0;
+		dev->cmb_size = 0;
 	}
 }
 
@@ -1889,13 +1899,13 @@ static int nvme_setup_io_queues(struct nvme_dev *dev)
 	if (nr_io_queues == 0)
 		return 0;
 
-	if (dev->cmb && (dev->cmbsz & NVME_CMBSZ_SQS)) {
+	if (dev->cmb_use_sqes) {
 		result = nvme_cmb_qdepth(dev, nr_io_queues,
 				sizeof(struct nvme_command));
 		if (result > 0)
 			dev->q_depth = result;
 		else
-			nvme_release_cmb(dev);
+			dev->cmb_use_sqes = false;
 	}
 
 	do {
-- 
2.19.0

[PATCH v6 10/13] nvme-pci: Add support for P2P memory in requests

[Logan Gunthorpe]

For P2P requests, we must use the pci_p2pmem_map_sg() function
instead of the dma_map_sg functions.

With that, we can then indicate PCI_P2P support in the request queue.
For this, we create an NVME_F_PCI_P2P flag which tells the core to
set QUEUE_FLAG_PCI_P2P in the request queue.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 drivers/nvme/host/core.c |  4 ++++
 drivers/nvme/host/nvme.h |  1 +
 drivers/nvme/host/pci.c  | 17 +++++++++++++----
 3 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index dd8ec1dd9219..6033ce2fd3e9 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3051,7 +3051,11 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid)
 	ns->queue = blk_mq_init_queue(ctrl->tagset);
 	if (IS_ERR(ns->queue))
 		goto out_free_ns;
+
 	blk_queue_flag_set(QUEUE_FLAG_NONROT, ns->queue);
+	if (ctrl->ops->flags & NVME_F_PCI_P2PDMA)
+		blk_queue_flag_set(QUEUE_FLAG_PCI_P2PDMA, ns->queue);
+
 	ns->queue->queuedata = ns;
 	ns->ctrl = ctrl;
 
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index bb4a2003c097..4030743c90aa 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -343,6 +343,7 @@ struct nvme_ctrl_ops {
 	unsigned int flags;
 #define NVME_F_FABRICS			(1 << 0)
 #define NVME_F_METADATA_SUPPORTED	(1 << 1)
+#define NVME_F_PCI_P2PDMA		(1 << 2)
 	int (*reg_read32)(struct nvme_ctrl *ctrl, u32 off, u32 *val);
 	int (*reg_write32)(struct nvme_ctrl *ctrl, u32 off, u32 val);
 	int (*reg_read64)(struct nvme_ctrl *ctrl, u32 off, u64 *val);
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index f434706a04e8..0d6c41bc2b35 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -745,8 +745,13 @@ static blk_status_t nvme_map_data(struct nvme_dev *dev, struct request *req,
 		goto out;
 
 	ret = BLK_STS_RESOURCE;
-	nr_mapped = dma_map_sg_attrs(dev->dev, iod->sg, iod->nents, dma_dir,
-			DMA_ATTR_NO_WARN);
+
+	if (is_pci_p2pdma_page(sg_page(iod->sg)))
+		nr_mapped = pci_p2pdma_map_sg(dev->dev, iod->sg, iod->nents,
+					  dma_dir);
+	else
+		nr_mapped = dma_map_sg_attrs(dev->dev, iod->sg, iod->nents,
+					     dma_dir,  DMA_ATTR_NO_WARN);
 	if (!nr_mapped)
 		goto out;
 
@@ -788,7 +793,10 @@ static void nvme_unmap_data(struct nvme_dev *dev, struct request *req)
 			DMA_TO_DEVICE : DMA_FROM_DEVICE;
 
 	if (iod->nents) {
-		dma_unmap_sg(dev->dev, iod->sg, iod->nents, dma_dir);
+		/* P2PDMA requests do not need to be unmapped */
+		if (!is_pci_p2pdma_page(sg_page(iod->sg)))
+			dma_unmap_sg(dev->dev, iod->sg, iod->nents, dma_dir);
+
 		if (blk_integrity_rq(req))
 			dma_unmap_sg(dev->dev, &iod->meta_sg, 1, dma_dir);
 	}
@@ -2400,7 +2408,8 @@ static int nvme_pci_get_address(struct nvme_ctrl *ctrl, char *buf, int size)
 static const struct nvme_ctrl_ops nvme_pci_ctrl_ops = {
 	.name			= "pcie",
 	.module			= THIS_MODULE,
-	.flags			= NVME_F_METADATA_SUPPORTED,
+	.flags			= NVME_F_METADATA_SUPPORTED |
+				  NVME_F_PCI_P2PDMA,
 	.reg_read32		= nvme_pci_reg_read32,
 	.reg_write32		= nvme_pci_reg_write32,
 	.reg_read64		= nvme_pci_reg_read64,
-- 
2.19.0

[PATCH v6 11/13] nvme-pci: Add a quirk for a pseudo CMB

[Logan Gunthorpe]

Introduce a quirk to use CMB-like memory on older devices that have
an exposed BAR but do not advertise support for using CMBLOC and
CMBSIZE.

We'd like to use some of these older cards to test P2P memory.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
---
 drivers/nvme/host/nvme.h |  7 +++++++
 drivers/nvme/host/pci.c  | 24 ++++++++++++++++++++----
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 4030743c90aa..8e6f3bcfe956 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -90,6 +90,13 @@ enum nvme_quirks {
 	 * Set MEDIUM priority on SQ creation
 	 */
 	NVME_QUIRK_MEDIUM_PRIO_SQ		= (1 << 7),
+
+	/*
+	 * Pseudo CMB Support on BAR 4. For adapters like the Microsemi
+	 * NVRAM that have CMB-like memory on a BAR but does not set
+	 * CMBLOC or CMBSZ.
+	 */
+	NVME_QUIRK_PSEUDO_CMB_BAR4		= (1 << 8),
 };
 
 /*
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 0d6c41bc2b35..db862ee6e53e 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -1644,6 +1644,13 @@ static ssize_t nvme_cmb_show(struct device *dev,
 }
 static DEVICE_ATTR(cmb, S_IRUGO, nvme_cmb_show, NULL);
 
+static u32 nvme_pseudo_cmbsz(struct pci_dev *pdev, int bar)
+{
+	return NVME_CMBSZ_WDS | NVME_CMBSZ_RDS |
+		(((ilog2(SZ_16M) - 12) / 4) << NVME_CMBSZ_SZU_SHIFT) |
+		((pci_resource_len(pdev, bar) / SZ_16M) << NVME_CMBSZ_SZ_SHIFT);
+}
+
 static u64 nvme_cmb_size_unit(struct nvme_dev *dev)
 {
 	u8 szu = (dev->cmbsz >> NVME_CMBSZ_SZU_SHIFT) & NVME_CMBSZ_SZU_MASK;
@@ -1663,10 +1670,15 @@ static void nvme_map_cmb(struct nvme_dev *dev)
 	struct pci_dev *pdev = to_pci_dev(dev->dev);
 	int bar;
 
-	dev->cmbsz = readl(dev->bar + NVME_REG_CMBSZ);
-	if (!dev->cmbsz)
-		return;
-	dev->cmbloc = readl(dev->bar + NVME_REG_CMBLOC);
+	if (dev->ctrl.quirks & NVME_QUIRK_PSEUDO_CMB_BAR4) {
+		dev->cmbsz = nvme_pseudo_cmbsz(pdev, 4);
+		dev->cmbloc = 4;
+	} else {
+		dev->cmbsz = readl(dev->bar + NVME_REG_CMBSZ);
+		if (!dev->cmbsz)
+			return;
+		dev->cmbloc = readl(dev->bar + NVME_REG_CMBLOC);
+	}
 
 	size = nvme_cmb_size_unit(dev) * nvme_cmb_size(dev);
 	offset = nvme_cmb_size_unit(dev) * NVME_CMB_OFST(dev->cmbloc);
@@ -2715,6 +2727,10 @@ static const struct pci_device_id nvme_id_table[] = {
 		.driver_data = NVME_QUIRK_LIGHTNVM, },
 	{ PCI_DEVICE(0x1d1d, 0x2601),	/* CNEX Granby */
 		.driver_data = NVME_QUIRK_LIGHTNVM, },
+	{ PCI_DEVICE(0x11f8, 0xf117),	/* Microsemi NVRAM adaptor */
+		.driver_data = NVME_QUIRK_PSEUDO_CMB_BAR4, },
+	{ PCI_DEVICE(0x1db1, 0x0002),	/* Everspin nvNitro adaptor */
+		.driver_data = NVME_QUIRK_PSEUDO_CMB_BAR4,  },
 	{ PCI_DEVICE_CLASS(PCI_CLASS_STORAGE_EXPRESS, 0xffffff) },
 	{ PCI_DEVICE(PCI_VENDOR_ID_APPLE, 0x2001) },
 	{ PCI_DEVICE(PCI_VENDOR_ID_APPLE, 0x2003) },
-- 
2.19.0

[PATCH v6 12/13] nvmet: Introduce helper functions to allocate and free request SGLs

[Logan Gunthorpe]

Add helpers to allocate and free the SGL in a struct nvmet_req:

int nvmet_req_alloc_sgl(struct nvmet_req *req, struct nvmet_sq *sq)
void nvmet_req_free_sgl(struct nvmet_req *req)

This will be expanded in a future patch to implement peer-to-peer
memory DMAs and should be common with all target drivers. The presently
unused 'sq' argument in the alloc function will be necessary to
decide whether to use peer-to-peer memory and obtain the correct
provider to allocate the memory.

The new helpers are used in nvmet-rdma. Seeing we use req.transfer_len
as the length of the SGL it is set earlier and cleared on any error.
It also seems to be unnecessary to accumulate the length as the map_sgl
functions should only ever be called once per request.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Sagi Grimberg <sagi@grimberg.me>
Cc: Christoph Hellwig <hch@lst.de>
---
 drivers/nvme/target/core.c  | 18 ++++++++++++++++++
 drivers/nvme/target/nvmet.h |  2 ++
 drivers/nvme/target/rdma.c  | 20 ++++++++++++--------
 3 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
index b5ec96abd048..bddd1599b826 100644
--- a/drivers/nvme/target/core.c
+++ b/drivers/nvme/target/core.c
@@ -725,6 +725,24 @@ void nvmet_req_execute(struct nvmet_req *req)
 }
 EXPORT_SYMBOL_GPL(nvmet_req_execute);
 
+int nvmet_req_alloc_sgl(struct nvmet_req *req, struct nvmet_sq *sq)
+{
+	req->sg = sgl_alloc(req->transfer_len, GFP_KERNEL, &req->sg_cnt);
+	if (!req->sg)
+		return -ENOMEM;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(nvmet_req_alloc_sgl);
+
+void nvmet_req_free_sgl(struct nvmet_req *req)
+{
+	sgl_free(req->sg);
+	req->sg = NULL;
+	req->sg_cnt = 0;
+}
+EXPORT_SYMBOL_GPL(nvmet_req_free_sgl);
+
 static inline bool nvmet_cc_en(u32 cc)
 {
 	return (cc >> NVME_CC_EN_SHIFT) & 0x1;
diff --git a/drivers/nvme/target/nvmet.h b/drivers/nvme/target/nvmet.h
index ec9af4ee03b6..7d6cb61021e4 100644
--- a/drivers/nvme/target/nvmet.h
+++ b/drivers/nvme/target/nvmet.h
@@ -336,6 +336,8 @@ bool nvmet_req_init(struct nvmet_req *req, struct nvmet_cq *cq,
 void nvmet_req_uninit(struct nvmet_req *req);
 void nvmet_req_execute(struct nvmet_req *req);
 void nvmet_req_complete(struct nvmet_req *req, u16 status);
+int nvmet_req_alloc_sgl(struct nvmet_req *req, struct nvmet_sq *sq);
+void nvmet_req_free_sgl(struct nvmet_req *req);
 
 void nvmet_cq_setup(struct nvmet_ctrl *ctrl, struct nvmet_cq *cq, u16 qid,
 		u16 size);
diff --git a/drivers/nvme/target/rdma.c b/drivers/nvme/target/rdma.c
index 3533e918ea37..e148dee72ba5 100644
--- a/drivers/nvme/target/rdma.c
+++ b/drivers/nvme/target/rdma.c
@@ -489,7 +489,7 @@ static void nvmet_rdma_release_rsp(struct nvmet_rdma_rsp *rsp)
 	}
 
 	if (rsp->req.sg != rsp->cmd->inline_sg)
-		sgl_free(rsp->req.sg);
+		nvmet_req_free_sgl(&rsp->req);
 
 	if (unlikely(!list_empty_careful(&queue->rsp_wr_wait_list)))
 		nvmet_rdma_process_wr_wait_list(queue);
@@ -638,24 +638,24 @@ static u16 nvmet_rdma_map_sgl_keyed(struct nvmet_rdma_rsp *rsp,
 {
 	struct rdma_cm_id *cm_id = rsp->queue->cm_id;
 	u64 addr = le64_to_cpu(sgl->addr);
-	u32 len = get_unaligned_le24(sgl->length);
 	u32 key = get_unaligned_le32(sgl->key);
 	int ret;
 
+	rsp->req.transfer_len = get_unaligned_le24(sgl->length);
+
 	/* no data command? */
-	if (!len)
+	if (!rsp->req.transfer_len)
 		return 0;
 
-	rsp->req.sg = sgl_alloc(len, GFP_KERNEL, &rsp->req.sg_cnt);
-	if (!rsp->req.sg)
-		return NVME_SC_INTERNAL;
+	ret = nvmet_req_alloc_sgl(&rsp->req, &rsp->queue->nvme_sq);
+	if (ret < 0)
+		goto error_out;
 
 	ret = rdma_rw_ctx_init(&rsp->rw, cm_id->qp, cm_id->port_num,
 			rsp->req.sg, rsp->req.sg_cnt, 0, addr, key,
 			nvmet_data_dir(&rsp->req));
 	if (ret < 0)
-		return NVME_SC_INTERNAL;
-	rsp->req.transfer_len += len;
+		goto error_out;
 	rsp->n_rdma += ret;
 
 	if (invalidate) {
@@ -664,6 +664,10 @@ static u16 nvmet_rdma_map_sgl_keyed(struct nvmet_rdma_rsp *rsp,
 	}
 
 	return 0;
+
+error_out:
+	rsp->req.transfer_len = 0;
+	return NVME_SC_INTERNAL;
 }
 
 static u16 nvmet_rdma_map_sgl(struct nvmet_rdma_rsp *rsp)
-- 
2.19.0

[PATCH v6 13/13] nvmet: Optionally use PCI P2P memory

[Logan Gunthorpe]

We create a configfs attribute in each nvme-fabrics target port to
enable p2p memory use. When enabled, the port will only then use the
p2p memory if a p2p memory device can be found which is behind the
same switch hierarchy as the RDMA port and all the block devices in
use. If the user enabled it and no devices are found, then the system
will silently fall back on using regular memory.

If appropriate, that port will allocate memory for the RDMA buffers
for queues from the p2pmem device falling back to system memory should
anything fail.

Ideally, we'd want to use an NVME CMB buffer as p2p memory. This would
save an extra PCI transfer as the NVME card could just take the data
out of it's own memory. However, at this time, only a limited number
of cards with CMB buffers seem to be available.

Signed-off-by: Stephen Bates <sbates@raithlin.com>
Signed-off-by: Steve Wise <swise@opengridcomputing.com>
[hch: partial rewrite of the initial code]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
 drivers/nvme/target/configfs.c    |  36 ++++++++
 drivers/nvme/target/core.c        | 138 +++++++++++++++++++++++++++++-
 drivers/nvme/target/io-cmd-bdev.c |   3 +
 drivers/nvme/target/nvmet.h       |  13 +++
 drivers/nvme/target/rdma.c        |   2 +
 5 files changed, 191 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/target/configfs.c b/drivers/nvme/target/configfs.c
index b37a8e3e3f80..0dfb0e0c3d21 100644
--- a/drivers/nvme/target/configfs.c
+++ b/drivers/nvme/target/configfs.c
@@ -17,6 +17,8 @@
 #include <linux/slab.h>
 #include <linux/stat.h>
 #include <linux/ctype.h>
+#include <linux/pci.h>
+#include <linux/pci-p2pdma.h>
 
 #include "nvmet.h"
 
@@ -1094,6 +1096,37 @@ static void nvmet_port_release(struct config_item *item)
 	kfree(port);
 }
 
+#ifdef CONFIG_PCI_P2PDMA
+static ssize_t nvmet_p2pmem_show(struct config_item *item, char *page)
+{
+	struct nvmet_port *port = to_nvmet_port(item);
+
+	return pci_p2pdma_enable_show(page, port->p2p_dev, port->use_p2pmem);
+}
+
+static ssize_t nvmet_p2pmem_store(struct config_item *item,
+		const char *page, size_t count)
+{
+	struct nvmet_port *port = to_nvmet_port(item);
+	struct pci_dev *p2p_dev = NULL;
+	bool use_p2pmem;
+	int error;
+
+	error = pci_p2pdma_enable_store(page, &p2p_dev, &use_p2pmem);
+	if (error)
+		return error;
+
+	down_write(&nvmet_config_sem);
+	port->use_p2pmem = use_p2pmem;
+	pci_dev_put(port->p2p_dev);
+	port->p2p_dev = p2p_dev;
+	up_write(&nvmet_config_sem);
+
+	return count;
+}
+CONFIGFS_ATTR(nvmet_, p2pmem);
+#endif /* CONFIG_PCI_P2PDMA */
+
 static struct configfs_attribute *nvmet_port_attrs[] = {
 	&nvmet_attr_addr_adrfam,
 	&nvmet_attr_addr_treq,
@@ -1101,6 +1134,9 @@ static struct configfs_attribute *nvmet_port_attrs[] = {
 	&nvmet_attr_addr_trsvcid,
 	&nvmet_attr_addr_trtype,
 	&nvmet_attr_param_inline_data_size,
+#ifdef CONFIG_PCI_P2PDMA
+	&nvmet_attr_p2pmem,
+#endif
 	NULL,
 };
 
diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
index bddd1599b826..7ade16cb4ed3 100644
--- a/drivers/nvme/target/core.c
+++ b/drivers/nvme/target/core.c
@@ -15,6 +15,7 @@
 #include <linux/module.h>
 #include <linux/random.h>
 #include <linux/rculist.h>
+#include <linux/pci-p2pdma.h>
 
 #include "nvmet.h"
 
@@ -365,9 +366,29 @@ static void nvmet_ns_dev_disable(struct nvmet_ns *ns)
 	nvmet_file_ns_disable(ns);
 }
 
+static int nvmet_p2pdma_add_client(struct nvmet_ctrl *ctrl,
+		struct nvmet_ns *ns)
+{
+	int ret;
+
+	if (!blk_queue_pci_p2pdma(ns->bdev->bd_queue)) {
+		pr_err("peer-to-peer DMA is not supported by %s\n",
+		       ns->device_path);
+		return -EINVAL;
+	}
+
+	ret = pci_p2pdma_add_client(&ctrl->p2p_clients, nvmet_ns_dev(ns));
+	if (ret)
+		pr_err("failed to add peer-to-peer DMA client %s: %d\n",
+		       ns->device_path, ret);
+
+	return ret;
+}
+
 int nvmet_ns_enable(struct nvmet_ns *ns)
 {
 	struct nvmet_subsys *subsys = ns->subsys;
+	struct nvmet_ctrl *ctrl;
 	int ret;
 
 	mutex_lock(&subsys->lock);
@@ -389,6 +410,14 @@ int nvmet_ns_enable(struct nvmet_ns *ns)
 	if (ret)
 		goto out_dev_put;
 
+	list_for_each_entry(ctrl, &subsys->ctrls, subsys_entry) {
+		if (ctrl->p2p_dev) {
+			ret = nvmet_p2pdma_add_client(ctrl, ns);
+			if (ret)
+				goto out_remove_clients;
+		}
+	}
+
 	if (ns->nsid > subsys->max_nsid)
 		subsys->max_nsid = ns->nsid;
 
@@ -417,6 +446,9 @@ int nvmet_ns_enable(struct nvmet_ns *ns)
 out_unlock:
 	mutex_unlock(&subsys->lock);
 	return ret;
+out_remove_clients:
+	list_for_each_entry(ctrl, &subsys->ctrls, subsys_entry)
+		pci_p2pdma_remove_client(&ctrl->p2p_clients, nvmet_ns_dev(ns));
 out_dev_put:
 	nvmet_ns_dev_disable(ns);
 	goto out_unlock;
@@ -425,6 +457,7 @@ int nvmet_ns_enable(struct nvmet_ns *ns)
 void nvmet_ns_disable(struct nvmet_ns *ns)
 {
 	struct nvmet_subsys *subsys = ns->subsys;
+	struct nvmet_ctrl *ctrl;
 
 	mutex_lock(&subsys->lock);
 	if (!ns->enabled)
@@ -450,6 +483,12 @@ void nvmet_ns_disable(struct nvmet_ns *ns)
 	percpu_ref_exit(&ns->ref);
 
 	mutex_lock(&subsys->lock);
+
+	list_for_each_entry(ctrl, &subsys->ctrls, subsys_entry) {
+		pci_p2pdma_remove_client(&ctrl->p2p_clients, nvmet_ns_dev(ns));
+		nvmet_add_async_event(ctrl, NVME_AER_TYPE_NOTICE, 0, 0);
+	}
+
 	subsys->nr_namespaces--;
 	nvmet_ns_changed(subsys, ns->nsid);
 	nvmet_ns_dev_disable(ns);
@@ -727,6 +766,23 @@ EXPORT_SYMBOL_GPL(nvmet_req_execute);
 
 int nvmet_req_alloc_sgl(struct nvmet_req *req, struct nvmet_sq *sq)
 {
+	struct pci_dev *p2p_dev = NULL;
+
+	if (IS_ENABLED(CONFIG_PCI_P2PDMA)) {
+		if (sq->ctrl)
+			p2p_dev = sq->ctrl->p2p_dev;
+
+		req->p2p_dev = NULL;
+		if (sq->qid && p2p_dev) {
+			req->sg = pci_p2pmem_alloc_sgl(p2p_dev, &req->sg_cnt,
+						       req->transfer_len);
+			if (req->sg) {
+				req->p2p_dev = p2p_dev;
+				return 0;
+			}
+		}
+	}
+
 	req->sg = sgl_alloc(req->transfer_len, GFP_KERNEL, &req->sg_cnt);
 	if (!req->sg)
 		return -ENOMEM;
@@ -737,7 +793,11 @@ EXPORT_SYMBOL_GPL(nvmet_req_alloc_sgl);
 
 void nvmet_req_free_sgl(struct nvmet_req *req)
 {
-	sgl_free(req->sg);
+	if (req->p2p_dev)
+		pci_p2pmem_free_sgl(req->p2p_dev, req->sg);
+	else
+		sgl_free(req->sg);
+
 	req->sg = NULL;
 	req->sg_cnt = 0;
 }
@@ -939,6 +999,79 @@ bool nvmet_host_allowed(struct nvmet_req *req, struct nvmet_subsys *subsys,
 		return __nvmet_host_allowed(subsys, hostnqn);
 }
 
+/*
+ * If allow_p2pmem is set, we will try to use P2P memory for the SGL lists for
+ * Ι/O commands. This requires the PCI p2p device to be compatible with the
+ * backing device for every namespace on this controller.
+ */
+static void nvmet_setup_p2pmem(struct nvmet_ctrl *ctrl, struct nvmet_req *req)
+{
+	struct nvmet_ns *ns;
+	int ret;
+
+	if (!req->port->use_p2pmem || !req->p2p_client)
+		return;
+
+	mutex_lock(&ctrl->subsys->lock);
+
+	ret = pci_p2pdma_add_client(&ctrl->p2p_clients, req->p2p_client);
+	if (ret) {
+		pr_err("failed adding peer-to-peer DMA client %s: %d\n",
+		       dev_name(req->p2p_client), ret);
+		goto free_devices;
+	}
+
+	list_for_each_entry_rcu(ns, &ctrl->subsys->namespaces, dev_link) {
+		ret = nvmet_p2pdma_add_client(ctrl, ns);
+		if (ret)
+			goto free_devices;
+	}
+
+	if (req->port->p2p_dev) {
+		/* A specific P2P device was selected in configfs */
+		if (!pci_p2pdma_assign_provider(req->port->p2p_dev,
+						&ctrl->p2p_clients)) {
+			pr_info("peer-to-peer memory on %s is not supported\n",
+				pci_name(req->port->p2p_dev));
+			goto free_devices;
+		}
+		ctrl->p2p_dev = pci_dev_get(req->port->p2p_dev);
+	} else {
+		/*
+		 * No P2P device was provided in configfs, therefore find one
+		 * automatically.
+		 */
+		ctrl->p2p_dev = pci_p2pmem_find(&ctrl->p2p_clients);
+		if (!ctrl->p2p_dev) {
+			pr_info("no supported peer-to-peer memory devices found\n");
+			goto free_devices;
+		}
+	}
+
+	mutex_unlock(&ctrl->subsys->lock);
+
+	pr_info("using peer-to-peer memory on %s\n", pci_name(ctrl->p2p_dev));
+	return;
+
+free_devices:
+	pci_p2pdma_client_list_free(&ctrl->p2p_clients);
+	mutex_unlock(&ctrl->subsys->lock);
+}
+
+static void nvmet_release_p2pmem(struct nvmet_ctrl *ctrl)
+{
+	if (!ctrl->p2p_dev)
+		return;
+
+	mutex_lock(&ctrl->subsys->lock);
+
+	pci_p2pdma_client_list_free(&ctrl->p2p_clients);
+	pci_dev_put(ctrl->p2p_dev);
+	ctrl->p2p_dev = NULL;
+
+	mutex_unlock(&ctrl->subsys->lock);
+}
+
 u16 nvmet_alloc_ctrl(const char *subsysnqn, const char *hostnqn,
 		struct nvmet_req *req, u32 kato, struct nvmet_ctrl **ctrlp)
 {
@@ -980,6 +1113,7 @@ u16 nvmet_alloc_ctrl(const char *subsysnqn, const char *hostnqn,
 
 	INIT_WORK(&ctrl->async_event_work, nvmet_async_event_work);
 	INIT_LIST_HEAD(&ctrl->async_events);
+	INIT_LIST_HEAD(&ctrl->p2p_clients);
 
 	memcpy(ctrl->subsysnqn, subsysnqn, NVMF_NQN_SIZE);
 	memcpy(ctrl->hostnqn, hostnqn, NVMF_NQN_SIZE);
@@ -1041,6 +1175,7 @@ u16 nvmet_alloc_ctrl(const char *subsysnqn, const char *hostnqn,
 		ctrl->kato = DIV_ROUND_UP(kato, 1000);
 	}
 	nvmet_start_keep_alive_timer(ctrl);
+	nvmet_setup_p2pmem(ctrl, req);
 
 	mutex_lock(&subsys->lock);
 	list_add_tail(&ctrl->subsys_entry, &subsys->ctrls);
@@ -1079,6 +1214,7 @@ static void nvmet_ctrl_free(struct kref *ref)
 	flush_work(&ctrl->async_event_work);
 	cancel_work_sync(&ctrl->fatal_err_work);
 
+	nvmet_release_p2pmem(ctrl);
 	ida_simple_remove(&cntlid_ida, ctrl->cntlid);
 
 	kfree(ctrl->sqs);
diff --git a/drivers/nvme/target/io-cmd-bdev.c b/drivers/nvme/target/io-cmd-bdev.c
index 7bc9f6240432..5660dd7ca755 100644
--- a/drivers/nvme/target/io-cmd-bdev.c
+++ b/drivers/nvme/target/io-cmd-bdev.c
@@ -78,6 +78,9 @@ static void nvmet_bdev_execute_rw(struct nvmet_req *req)
 		op = REQ_OP_READ;
 	}
 
+	if (is_pci_p2pdma_page(sg_page(req->sg)))
+		op_flags |= REQ_NOMERGE;
+
 	sector = le64_to_cpu(req->cmd->rw.slba);
 	sector <<= (req->ns->blksize_shift - 9);
 
diff --git a/drivers/nvme/target/nvmet.h b/drivers/nvme/target/nvmet.h
index 7d6cb61021e4..297861064dd8 100644
--- a/drivers/nvme/target/nvmet.h
+++ b/drivers/nvme/target/nvmet.h
@@ -84,6 +84,11 @@ static inline struct nvmet_ns *to_nvmet_ns(struct config_item *item)
 	return container_of(to_config_group(item), struct nvmet_ns, group);
 }
 
+static inline struct device *nvmet_ns_dev(struct nvmet_ns *ns)
+{
+	return disk_to_dev(ns->bdev->bd_disk);
+}
+
 struct nvmet_cq {
 	u16			qid;
 	u16			size;
@@ -134,6 +139,8 @@ struct nvmet_port {
 	void				*priv;
 	bool				enabled;
 	int				inline_data_size;
+	bool				use_p2pmem;
+	struct pci_dev			*p2p_dev;
 };
 
 static inline struct nvmet_port *to_nvmet_port(struct config_item *item)
@@ -182,6 +189,9 @@ struct nvmet_ctrl {
 	__le32			*changed_ns_list;
 	u32			nr_changed_ns;
 
+	struct pci_dev		*p2p_dev;
+	struct list_head	p2p_clients;
+
 	char			subsysnqn[NVMF_NQN_FIELD_LEN];
 	char			hostnqn[NVMF_NQN_FIELD_LEN];
 };
@@ -294,6 +304,9 @@ struct nvmet_req {
 
 	void (*execute)(struct nvmet_req *req);
 	const struct nvmet_fabrics_ops *ops;
+
+	struct pci_dev *p2p_dev;
+	struct device *p2p_client;
 };
 
 extern struct workqueue_struct *buffered_io_wq;
diff --git a/drivers/nvme/target/rdma.c b/drivers/nvme/target/rdma.c
index e148dee72ba5..5c9cb752e2ed 100644
--- a/drivers/nvme/target/rdma.c
+++ b/drivers/nvme/target/rdma.c
@@ -735,6 +735,8 @@ static void nvmet_rdma_handle_command(struct nvmet_rdma_queue *queue,
 		cmd->send_sge.addr, cmd->send_sge.length,
 		DMA_TO_DEVICE);
 
+	cmd->req.p2p_client = &queue->dev->device->dev;
+
 	if (!nvmet_req_init(&cmd->req, &queue->nvme_cq,
 			&queue->nvme_sq, &nvmet_rdma_ops))
 		return;
-- 
2.19.0

Re: [PATCH v6 07/13] block: Add PCI P2P flag for request queue and check support for requests

[Jens Axboe]

On 9/12/18 6:11 PM, Logan Gunthorpe wrote:
> QUEUE_FLAG_PCI_P2P is introduced meaning a driver's request queue
> supports targeting P2P memory.
> 
> When a request is submitted we check if PCI P2PDMA memory is assigned
> to the first page in the bio. If it is, we ensure the queue it's
> submitted to supports it, and enforce REQ_NOMERGE.

This changelog is no longer accurate.

-- 
Jens Axboe

Re: [PATCH v6 07/13] block: Add PCI P2P flag for request queue and check support for requests

[Logan Gunthorpe]

On 12/09/18 06:28 PM, Jens Axboe wrote:
> On 9/12/18 6:11 PM, Logan Gunthorpe wrote:
>> QUEUE_FLAG_PCI_P2P is introduced meaning a driver's request queue
>> supports targeting P2P memory.
>>
>> When a request is submitted we check if PCI P2PDMA memory is assigned
>> to the first page in the bio. If it is, we ensure the queue it's
>> submitted to supports it, and enforce REQ_NOMERGE.
> 
> This changelog is no longer accurate.


Oops, I'll fix this for v7.

Thanks,

Logan

Re: [PATCH v6 01/13] PCI/P2PDMA: Support peer-to-peer memory

[Bjorn Helgaas]

On Wed, Sep 12, 2018 at 06:11:44PM -0600, Logan Gunthorpe wrote:
> Some PCI devices may have memory mapped in a BAR space that's
> intended for use in peer-to-peer transactions. In order to enable
> such transactions the memory must be registered with ZONE_DEVICE pages
> so it can be used by DMA interfaces in existing drivers.
> 
> Add an interface for other subsystems to find and allocate chunks of P2P
> memory as necessary to facilitate transfers between two PCI peers:
> 
> int pci_p2pdma_add_client();
> struct pci_dev *pci_p2pmem_find();
> void *pci_alloc_p2pmem();
> 
> The new interface requires a driver to collect a list of client devices
> involved in the transaction with the pci_p2pmem_add_client*() functions
> then call pci_p2pmem_find() to obtain any suitable P2P memory. Once
> this is done the list is bound to the memory and the calling driver is
> free to add and remove clients as necessary (adding incompatible clients
> will fail). With a suitable p2pmem device, memory can then be
> allocated with pci_alloc_p2pmem() for use in DMA transactions.
> 
> Depending on hardware, using peer-to-peer memory may reduce the bandwidth
> of the transfer but can significantly reduce pressure on system memory.
> This may be desirable in many cases: for example a system could be designed
> with a small CPU connected to a PCIe switch by a small number of lanes
> which would maximize the number of lanes available to connect to NVMe
> devices.
> 
> The code is designed to only utilize the p2pmem device if all the devices
> involved in a transfer are behind the same PCI bridge. This is because we
> have no way of knowing whether peer-to-peer routing between PCIe Root Ports
> is supported (PCIe r4.0, sec 1.3.1). Additionally, the benefits of P2P
> transfers that go through the RC is limited to only reducing DRAM usage
> and, in some cases, coding convenience. The PCI-SIG may be exploring
> adding a new capability bit to advertise whether this is possible for
> future hardware.
> 
> This commit includes significant rework and feedback from Christoph
> Hellwig.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>  # PCI pieces

Mostly trivial comments below.  Thanks for persevering with this!

> ---
>  drivers/pci/Kconfig        |  17 +
>  drivers/pci/Makefile       |   1 +
>  drivers/pci/p2pdma.c       | 761 +++++++++++++++++++++++++++++++++++++
>  include/linux/memremap.h   |   5 +
>  include/linux/mm.h         |  18 +
>  include/linux/pci-p2pdma.h | 102 +++++
>  include/linux/pci.h        |   4 +
>  7 files changed, 908 insertions(+)
>  create mode 100644 drivers/pci/p2pdma.c
>  create mode 100644 include/linux/pci-p2pdma.h

> +#define pr_fmt(fmt) "pci-p2pdma: " fmt

Is pr_fmt() actually used anywhere?

> + * Check if a PCI bridge has it's ACS redirection bits set to redirect P2P

s/it's/its/

> + * TLPs upstream via ACS. Returns 1 if the packets will be redirected
> + * upstream, 0 otherwise.
> + */
> +static int pci_bridge_has_acs_redir(struct pci_dev *dev)

Most of your code uses "pdev" for a struct pci_dev *.

> +static void seq_buf_print_bus_devfn(struct seq_buf *buf, struct pci_dev *dev)
> +{
> +	if (!buf)
> +		return;
> +
> +	seq_buf_printf(buf, "%04x:%02x:%02x.%x;", pci_domain_nr(dev->bus),
> +		       dev->bus->number, PCI_SLOT(dev->devfn),
> +		       PCI_FUNC(dev->devfn));

dev vs pdev?
I think you could use pci_name() here (see pci_setup_device()).

> + * In the case where two devices are connected to different PCIe switches,
> + * this function will still return a positive distance as long as both
> + * switches evenutally have a common upstream bridge. Note this covers

s/evenutally/eventually/

> +static int upstream_bridge_distance_warn(struct pci_dev *provider,
> +					 struct pci_dev *client)
> +{
> +	struct seq_buf acs_list;
> +	int ret;
> +
> +	seq_buf_init(&acs_list, kmalloc(PAGE_SIZE, GFP_KERNEL), PAGE_SIZE);

Check for kmalloc() failure here?  Failure would mean acs_list->buffer is
NULL, but I gave up following the chain to see how that would be handled.

> +
> +	ret = upstream_bridge_distance(provider, client, &acs_list);
> +	if (ret == -2) {
> +		pci_warn(client, "cannot be used for peer-to-peer DMA as ACS redirect is set between the client and provider\n");

Maybe include pci_name(provider) in these messages?

> +		/* Drop final semicolon */
> +		acs_list.buffer[acs_list.len-1] = 0;
> +		pci_warn(client, "to disable ACS redirect for this path, add the kernel parameter: pci=disable_acs_redir=%s\n",
> +			 acs_list.buffer);
> +
> +	} else if (ret < 0) {
> +		pci_warn(client, "cannot be used for peer-to-peer DMA as the client and provider do not share an upstream bridge\n");

> + * pci_p2pdma_assign_provider - Check compatibily (as per pci_p2pdma_distance)

s/compatibily/compatibility/

> +struct pci_dev *pci_p2pmem_find(struct list_head *clients)
> +{
> +	struct pci_dev *pdev = NULL;
> +	struct pci_p2pdma_client *pos;
> +	int distance;
> +	int closest_distance = INT_MAX;
> +	struct pci_dev **closest_pdevs;
> +	int dev_cnt = 0;
> +	const int max_devs = PAGE_SIZE / sizeof(*closest_pdevs);
> +	int i;
> +
> +	closest_pdevs = kmalloc(PAGE_SIZE, GFP_KERNEL);

Check for kmalloc() failure?

> +++ b/include/linux/pci-p2pdma.h
> @@ -0,0 +1,102 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * PCI Peer 2 Peer DMA support.
> + *
> + * Copyright (c) 2016-2018, Logan Gunthorpe
> + * Copyright (c) 2016-2017, Microsemi Corporation
> + * Copyright (c) 2017, Christoph Hellwig
> + * Copyright (c) 2018, Eideticom Inc.
> + *

Spurious blank line.

> + */

Re: [PATCH v6 01/13] PCI/P2PDMA: Support peer-to-peer memory

[Logan Gunthorpe]

On 2018-09-20 4:38 PM, Bjorn Helgaas wrote:
> Acked-by: Bjorn Helgaas <bhelgaas@google.com>  # PCI pieces
> 
> Mostly trivial comments below.  Thanks for persevering with this!

Thanks Bjorn. I'll make these fixes for v7 next week.
>> +#define pr_fmt(fmt) "pci-p2pdma: " fmt
> 
> Is pr_fmt() actually used anywhere?

It's used in a Patch 4 to print errors in the configfs helpers.

Logan

Re: [PATCH v6 01/13] PCI/P2PDMA: Support peer-to-peer memory

[Bjorn Helgaas]

On Thu, Sep 20, 2018 at 04:47:49PM -0600, Logan Gunthorpe wrote:
> On 2018-09-20 4:38 PM, Bjorn Helgaas wrote:
> >> +#define pr_fmt(fmt) "pci-p2pdma: " fmt
> > 
> > Is pr_fmt() actually used anywhere?
> 
> It's used in a Patch 4 to print errors in the configfs helpers.

Ideally pr_fmt() would be added in the same patch that uses it, but
obviously pretty trivial.

Re: [PATCH v6 02/13] PCI/P2PDMA: Add sysfs group to display p2pmem stats

[Bjorn Helgaas]

On Wed, Sep 12, 2018 at 06:11:45PM -0600, Logan Gunthorpe wrote:
> Add a sysfs group to display statistics about P2P memory that is
> registered in each PCI device.
> 
> Attributes in the group display the total amount of P2P memory, the
> amount available and whether it is published or not.
> 
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> +What:		/sys/bus/pci/devices/.../p2pmem/available
> +Date:		November 2017
> +Contact:	Logan Gunthorpe <logang@deltatee.com>
> +Description:
> +		If the device has any Peer-to-Peer memory registered, this
> +	        file contains the amount of memory that has not been
> +		allocated (in decimal).
> +
> +What:		/sys/bus/pci/devices/.../p2pmem/size
> +Date:		November 2017
> +Contact:	Logan Gunthorpe <logang@deltatee.com>
> +Description:
> +		If the device has any Peer-to-Peer memory registered, this
> +	        file contains the total amount of memory that the device
> +		provides (in decimal).

Maybe reorder this so the "size" (total amount) is documented before
"available" (some subset of "size")?

> +
> +What:		/sys/bus/pci/devices/.../p2pmem/published
> +Date:		November 2017
> +Contact:	Logan Gunthorpe <logang@deltatee.com>
> +Description:
> +		If the device has any Peer-to-Peer memory registered, this
> +	        file contains a '1' if the memory has been published for
> +		use inside the kernel or a '0' if it is only intended
> +		for use within the driver that published it.

It doesn't read quite right to talk about "use within the driver that
*published* it".  Is it really published in that case?  That sounds more
like "private".  I expected something like the following (but I don't claim
to understand the whole use model here):

  ... this file contains a '1' if the memory has been published for use
  outside the driver that owns the device.

Re: [PATCH v6 03/13] PCI/P2PDMA: Add PCI p2pmem DMA mappings to adjust the bus offset

[Bjorn Helgaas]

On Wed, Sep 12, 2018 at 06:11:46PM -0600, Logan Gunthorpe wrote:
> The DMA address used when mapping PCI P2P memory must be the PCI bus
> address. Thus, introduce pci_p2pmem_map_sg() to map the correct
> addresses when using P2P memory. Memory mapped in this way does not
> need to be unmapped.

I think the use of "map" in this context is slightly confusing because the
general expectation is that map/unmap must be balanced.

I assume it's because the "mapping" consumes no resources, e.g., requires
no page table entries.  Possibly there's a better verb than "map", e.g.,
"convert", "convert_to_p2pdma", etc?

If you keep "map", maybe add a sentence or two about why there's no
corresponding unmap?

> For this, we assume that an SGL passed to these functions contain all
> P2P memory or no P2P memory.
> 
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
>  drivers/pci/p2pdma.c       | 43 ++++++++++++++++++++++++++++++++++++++
>  include/linux/memremap.h   |  1 +
>  include/linux/pci-p2pdma.h |  7 +++++++
>  3 files changed, 51 insertions(+)
> 
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 67c1daf1189e..29bd40a87768 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -191,6 +191,8 @@ int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
>  	pgmap->res.flags = pci_resource_flags(pdev, bar);
>  	pgmap->ref = &pdev->p2pdma->devmap_ref;
>  	pgmap->type = MEMORY_DEVICE_PCI_P2PDMA;
> +	pgmap->pci_p2pdma_bus_offset = pci_bus_address(pdev, bar) -
> +		pci_resource_start(pdev, bar);
>  
>  	addr = devm_memremap_pages(&pdev->dev, pgmap);
>  	if (IS_ERR(addr)) {
> @@ -813,3 +815,44 @@ void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
>  	pdev->p2pdma->p2pmem_published = publish;
>  }
>  EXPORT_SYMBOL_GPL(pci_p2pmem_publish);
> +
> +/**
> + * pci_p2pdma_map_sg - map a PCI peer-to-peer scatterlist for DMA
> + * @dev: device doing the DMA request
> + * @sg: scatter list to map
> + * @nents: elements in the scatterlist
> + * @dir: DMA direction
> + *
> + * Scatterlists mapped with this function should not be unmapped in any way.
> + *
> + * Returns the number of SG entries mapped or 0 on error.
> + */
> +int pci_p2pdma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
> +		      enum dma_data_direction dir)
> +{
> +	struct dev_pagemap *pgmap;
> +	struct scatterlist *s;
> +	phys_addr_t paddr;
> +	int i;
> +
> +	/*
> +	 * p2pdma mappings are not compatible with devices that use
> +	 * dma_virt_ops. If the upper layers do the right thing
> +	 * this should never happen because it will be prevented
> +	 * by the check in pci_p2pdma_add_client()
> +	 */
> +	if (WARN_ON_ONCE(IS_ENABLED(CONFIG_DMA_VIRT_OPS) &&
> +			 dev->dma_ops == &dma_virt_ops))
> +		return 0;
> +
> +	for_each_sg(sg, s, nents, i) {
> +		pgmap = sg_page(s)->pgmap;
> +		paddr = sg_phys(s);
> +
> +		s->dma_address = paddr - pgmap->pci_p2pdma_bus_offset;
> +		sg_dma_len(s) = s->length;
> +	}
> +
> +	return nents;
> +}
> +EXPORT_SYMBOL_GPL(pci_p2pdma_map_sg);
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 9553370ebdad..0ac69ddf5fc4 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -125,6 +125,7 @@ struct dev_pagemap {
>  	struct device *dev;
>  	void *data;
>  	enum memory_type type;
> +	u64 pci_p2pdma_bus_offset;
>  };
>  
>  #ifdef CONFIG_ZONE_DEVICE
> diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h
> index 7b2b0f547528..2f03dbbf5af6 100644
> --- a/include/linux/pci-p2pdma.h
> +++ b/include/linux/pci-p2pdma.h
> @@ -36,6 +36,8 @@ struct scatterlist *pci_p2pmem_alloc_sgl(struct pci_dev *pdev,
>  					 unsigned int *nents, u32 length);
>  void pci_p2pmem_free_sgl(struct pci_dev *pdev, struct scatterlist *sgl);
>  void pci_p2pmem_publish(struct pci_dev *pdev, bool publish);
> +int pci_p2pdma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
> +		      enum dma_data_direction dir);
>  #else /* CONFIG_PCI_P2PDMA */
>  static inline int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar,
>  		size_t size, u64 offset)
> @@ -98,5 +100,10 @@ static inline void pci_p2pmem_free_sgl(struct pci_dev *pdev,
>  static inline void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
>  {
>  }
> +static inline int pci_p2pdma_map_sg(struct device *dev,
> +		struct scatterlist *sg, int nents, enum dma_data_direction dir)
> +{
> +	return 0;
> +}
>  #endif /* CONFIG_PCI_P2PDMA */
>  #endif /* _LINUX_PCI_P2P_H */
> -- 
> 2.19.0
> 

Re: [PATCH v6 01/13] PCI/P2PDMA: Support peer-to-peer memory

[Logan Gunthorpe]

On 2018-09-21 7:00 AM, Bjorn Helgaas wrote:
> On Thu, Sep 20, 2018 at 04:47:49PM -0600, Logan Gunthorpe wrote:
>> On 2018-09-20 4:38 PM, Bjorn Helgaas wrote:
>>>> +#define pr_fmt(fmt) "pci-p2pdma: " fmt
>>>
>>> Is pr_fmt() actually used anywhere?
>>
>> It's used in a Patch 4 to print errors in the configfs helpers.
> 
> Ideally pr_fmt() would be added in the same patch that uses it, but
> obviously pretty trivial.

Hmm, well Christoph asked me to do it this way. ;)

Logan

Re: [PATCH v6 01/13] PCI/P2PDMA: Support peer-to-peer memory

[Christoph Hellwig]

On Fri, Sep 21, 2018 at 09:37:33AM -0600, Logan Gunthorpe wrote:
> On 2018-09-21 7:00 AM, Bjorn Helgaas wrote:
> > On Thu, Sep 20, 2018 at 04:47:49PM -0600, Logan Gunthorpe wrote:
> >> On 2018-09-20 4:38 PM, Bjorn Helgaas wrote:
> >>>> +#define pr_fmt(fmt) "pci-p2pdma: " fmt
> >>>
> >>> Is pr_fmt() actually used anywhere?
> >>
> >> It's used in a Patch 4 to print errors in the configfs helpers.
> > 
> > Ideally pr_fmt() would be added in the same patch that uses it, but
> > obviously pretty trivial.
> 
> Hmm, well Christoph asked me to do it this way. ;)

Sorry.  I somehow was under the impression we already had a printk
in the earlier patch, but it looks like I was confused.

Re: [PATCH v6 04/13] PCI/P2PDMA: Introduce configfs/sysfs enable attribute helpers

[Bjorn Helgaas]

On Wed, Sep 12, 2018 at 06:11:47PM -0600, Logan Gunthorpe wrote:
> Users of the P2PDMA infrastructure will typically need a way for
> the user to tell the kernel to use P2P resources. Typically
> this will be a simple on/off boolean operation but sometimes
> it may be desirable for the user to specify the exact device to
> use for the P2P operation.
> 
> Add new helpers for attributes which take a boolean or a PCI device.
> Any boolean, or the word 'auto' turn P2P on or off. Specifying a full
> PCI device name/BDF will select the specific device.

I think examples of the valid booleans would be useful.  "Boolean"
suggests true/false, but AFAICT strtobool() only works for things
like 0/1/on/off.

What's the need for "auto"?  Sounds like it's equivalent to "on" but
it's not obvious why we need both.

It'd be sort of nice if the contents of the sysfs file were valid
things you could put *back* into it.  But it looks like the contents
might be "none", which isn't valid for the store.  And the contents
are never "on" or "off".

Where do these store/show functions get connected to sysfs?  I know
there's a lot of magic there, so apologies if I'm missing it.

> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> ---
>  drivers/pci/p2pdma.c       | 83 ++++++++++++++++++++++++++++++++++++++
>  include/linux/pci-p2pdma.h | 15 +++++++
>  2 files changed, 98 insertions(+)
> 
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 29bd40a87768..3da848f3fe72 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -9,6 +9,7 @@
>   */
>  
>  #define pr_fmt(fmt) "pci-p2pdma: " fmt
> +#include <linux/ctype.h>
>  #include <linux/pci-p2pdma.h>
>  #include <linux/module.h>
>  #include <linux/slab.h>
> @@ -856,3 +857,85 @@ int pci_p2pdma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
>  	return nents;
>  }
>  EXPORT_SYMBOL_GPL(pci_p2pdma_map_sg);
> +
> +/**
> + * pci_p2pdma_enable_store - parse a configfs/sysfs attribute store
> + *		to enable p2pdma
> + * @page: contents of the value to be stored
> + * @p2p_dev: returns the PCI device that was selected to be used
> + *		(if 'auto', 'none or a boolean isn't the store value)
> + * @use_p2pdma: returns whether to enable p2pdma or not
> + *
> + * Parses an attribute value to decide whether to enable p2pdma.
> + * The value can select a PCI device (using it's full BDF device
> + * name), a boolean, or 'auto'. 'auto' and a true boolean value
> + * have the same meaning. A false value disables p2pdma and
> + * a PCI device enables it to use a specific device as the
> + * backing provider.
> + *
> + * pci_p2pdma_enable_show() should be used as the show operation for
> + * the attribute.
> + *
> + * Returns 0 on success
> + */
> +int pci_p2pdma_enable_store(const char *page, struct pci_dev **p2p_dev,
> +			    bool *use_p2pdma)
> +{
> +	struct device *dev;
> +
> +	dev = bus_find_device_by_name(&pci_bus_type, NULL, page);
> +	if (dev) {
> +		*use_p2pdma = true;
> +		*p2p_dev = to_pci_dev(dev);
> +
> +		if (!pci_has_p2pmem(*p2p_dev)) {
> +			pr_err("PCI device has no peer-to-peer memory: %s\n",

pci_err()?

> +			       page);
> +			pci_dev_put(*p2p_dev);
> +			return -ENODEV;
> +		}
> +
> +		return 0;
> +	} else if (sysfs_streq(page, "auto")) {
> +		*use_p2pdma = true;
> +		return 0;
> +	} else if ((page[0] == '0' || page[0] == '1') && !iscntrl(page[1])) {
> +		/*
> +		 * If the user enters a PCI device that  doesn't exist
> +		 * like "0000:01:00.1", we don't want strtobool to think
> +		 * it's a '0' when it's clearly not what the user wanted.
> +		 * So we require 0's and 1's to be exactly one character.
> +		 */
> +	} else if (!strtobool(page, use_p2pdma)) {
> +		return 0;
> +	}
> +
> +	pr_err("No such PCI device: %.*s\n", (int)strcspn(page, "\n"), page);
> +	return -ENODEV;
> +}
> +EXPORT_SYMBOL_GPL(pci_p2pdma_enable_store);
> +
> +/**
> + * pci_p2pdma_enable_show - show a configfs/sysfs attribute indicating
> + *		whether p2pdma is enabled
> + * @page: contents of the stored value
> + * @p2p_dev: the selected p2p device (NULL if no device is selected)
> + * @use_p2pdma: whether p2pdme has been enabled
> + *
> + * Attributes that use pci_p2pdma_enable_store() should use this function
> + * to show the value of the attribute.
> + *
> + * Returns 0 on success
> + */
> +ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
> +			       bool use_p2pdma)
> +{
> +	if (!use_p2pdma)
> +		return sprintf(page, "none\n");
> +
> +	if (!p2p_dev)
> +		return sprintf(page, "auto\n");
> +
> +	return sprintf(page, "%s\n", pci_name(p2p_dev));
> +}
> +EXPORT_SYMBOL_GPL(pci_p2pdma_enable_show);
> diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h
> index 2f03dbbf5af6..377de4d73767 100644
> --- a/include/linux/pci-p2pdma.h
> +++ b/include/linux/pci-p2pdma.h
> @@ -38,6 +38,10 @@ void pci_p2pmem_free_sgl(struct pci_dev *pdev, struct scatterlist *sgl);
>  void pci_p2pmem_publish(struct pci_dev *pdev, bool publish);
>  int pci_p2pdma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
>  		      enum dma_data_direction dir);
> +int pci_p2pdma_enable_store(const char *page, struct pci_dev **p2p_dev,
> +			    bool *use_p2pdma);
> +ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
> +			       bool use_p2pdma);
>  #else /* CONFIG_PCI_P2PDMA */
>  static inline int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar,
>  		size_t size, u64 offset)
> @@ -105,5 +109,16 @@ static inline int pci_p2pdma_map_sg(struct device *dev,
>  {
>  	return 0;
>  }
> +static inline int pci_p2pdma_enable_store(const char *page,
> +		struct pci_dev **p2p_dev, bool *use_p2pdma)
> +{
> +	*use_p2pdma = false;
> +	return 0;
> +}
> +static inline ssize_t pci_p2pdma_enable_show(char *page,
> +		struct pci_dev *p2p_dev, bool use_p2pdma)
> +{
> +	return sprintf(page, "none\n");
> +}
>  #endif /* CONFIG_PCI_P2PDMA */
>  #endif /* _LINUX_PCI_P2P_H */
> -- 
> 2.19.0
> 

Re: [PATCH v6 06/13] PCI/P2PDMA: Add P2P DMA driver writer's documentation

[Bjorn Helgaas]

On Wed, Sep 12, 2018 at 06:11:49PM -0600, Logan Gunthorpe wrote:
> Add a restructured text file describing how to write drivers
> with support for P2P DMA transactions. The document describes
> how to use the APIs that were added in the previous few
> commits.
> 
> Also adds an index for the PCI documentation tree even though this
> is the only PCI document that has been converted to restructured text
> at this time.
> 
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> +With the client list in hand, the orchestrator may then call
> +:c:func:`pci_p2pmem_find()` to obtain a published P2P memory provider
> +that is supported (behind the same root port) as all the clients. If more
> +than one provider is supported, the one nearest to all the clients will
> +be chosen first. If there are more than one provider is an equal distance

s/If there are more/If more/

> +away, the one returned will be chosen at random. This function returns the PCI

s/the one returned will be chosen at random/one will be chosen
arbitrarily/ ?  (I doubt it's really random)

> +device to use for the provider with a reference taken and therefore
> +when it's no longer needed it should be returned with pci_dev_put().

> +Struct Page Caveats
> +-------------------
> +
> +Driver writers should be very careful about not passing these special
> +struct pages to code that isn't prepared for it. At this time, the kernel
> +interfaces do not have any checks for ensuring this. This obviously
> +precludes passing these pages to userspace.

Sounds like landmines here since the reader probably can't translate
"code that isn't prepared for it" into a list of interfaces that are
off-limits.  But that's a VM issue that is above my pay grade, so I'm
not suggesting any change; just pointing out something that makes me
wonder "hmmm..., how would I act on this?"

> +P2P memory is also technically IO memory but should never have any side
> +effects behind it. Thus, the order of loads and stores should not be important
> +and ioreadX(), iowriteX() and friends should not be necessary.
> +However, as the memory is not cache coherent, if access ever needs to
> +be protected by a spinlock then :c:func:`mmiowb()` must be used before
> +unlocking the lock. (See ACQUIRES VS I/O ACCESSES in
> +Documentation/memory-barriers.txt)

Re: [PATCH v6 03/13] PCI/P2PDMA: Add PCI p2pmem DMA mappings to adjust the bus offset

[Bjorn Helgaas]

On Fri, Sep 21, 2018 at 08:15:50AM -0500, Bjorn Helgaas wrote:
> On Wed, Sep 12, 2018 at 06:11:46PM -0600, Logan Gunthorpe wrote:
> > The DMA address used when mapping PCI P2P memory must be the PCI bus
> > address. Thus, introduce pci_p2pmem_map_sg() to map the correct
> > addresses when using P2P memory. Memory mapped in this way does not
> > need to be unmapped.
> 
> I think the use of "map" in this context is slightly confusing because the
> general expectation is that map/unmap must be balanced.
> 
> I assume it's because the "mapping" consumes no resources, e.g., requires
> no page table entries.  Possibly there's a better verb than "map", e.g.,
> "convert", "convert_to_p2pdma", etc?
> 
> If you keep "map", maybe add a sentence or two about why there's no
> corresponding unmap?

Another wrinkle is that "map" usually takes an A and gives you back a
B.  Now the caller has both A and B and both are still valid.

Here we pass in an SGL and the SGL is transformed, so the caller only
has B and A has been destroyed, i.e., the SGL can no longer be used as
it was before, and there's no way to get A back.

Maybe this is pointless bikeshedding, so if your color is the best,
don't change anything.

Bjorn

Re: [PATCH v6 06/13] PCI/P2PDMA: Add P2P DMA driver writer's documentation

[Logan Gunthorpe]

On 2018-09-21 10:41 AM, Bjorn Helgaas wrote:
>> +away, the one returned will be chosen at random. This function returns the PCI
> 
> s/the one returned will be chosen at random/one will be chosen
> arbitrarily/ ?  (I doubt it's really random)

You're the second person to ask this, but yes, we really do it randomly.
Such that if there are multiple drivers getting resources they should be
evenly distributed. It's not the ideal solution but if it were to do it
arbitrarily then the code would likely return the same device all the
time and any additional devices would not get used.

>> +Struct Page Caveats
>> +-------------------
>> +
>> +Driver writers should be very careful about not passing these special
>> +struct pages to code that isn't prepared for it. At this time, the kernel
>> +interfaces do not have any checks for ensuring this. This obviously
>> +precludes passing these pages to userspace.
> 
> Sounds like landmines here since the reader probably can't translate
> "code that isn't prepared for it" into a list of interfaces that are
> off-limits.  But that's a VM issue that is above my pay grade, so I'm
> not suggesting any change; just pointing out something that makes me
> wonder "hmmm..., how would I act on this?"

Yes, these are big landmines. These are the problems we have been
fighting with trying to get P2P memory into the kernel and the first
step seems to have settled on the developer using them has to be careful
and ensure they are only sent to paths that are used correctly. This
series does these things in the block layer and RDMA interface, but due
to Jens not wanting to add warnings to the common code, it's still
possible for a developer to code something that sends these pages to
block devices that are not prepared for it.

Logan

Re: [PATCH v6 03/13] PCI/P2PDMA: Add PCI p2pmem DMA mappings to adjust the bus offset

[Logan Gunthorpe]

On 2018-09-21 10:48 AM, Bjorn Helgaas wrote:
>> I think the use of "map" in this context is slightly confusing because the
>> general expectation is that map/unmap must be balanced.

Yeah, Jason said the same thing, but having an empty unmap function
seems wasteful and Christoph said to just remove it. My opinion is that
it's not that big an issue one way or another -- if we have to add an
unmap later it's not really that hard.

>> If you keep "map", maybe add a sentence or two about why there's no
>> corresponding unmap?

Will do.

> Another wrinkle is that "map" usually takes an A and gives you back a
> B.  Now the caller has both A and B and both are still valid.
> Here we pass in an SGL and the SGL is transformed, so the caller only
> has B and A has been destroyed, i.e., the SGL can no longer be used as
> it was before, and there's no way to get A back.

I wouldn't say that. Our map_sg function is doing the same thing
dma_map_sg is: it sets the DMA address and length in the scatter list.
So B is still A just with other fields set. If the caller wanted to map
this SG in a different way they can still do so and the new DMA
address/length would override the old values. (Normally, you'd want to
unmap before doing something like that, but seeing our unmap is an empty
operation, we wouldn't have to do that.)

Logan

Re: [PATCH v6 04/13] PCI/P2PDMA: Introduce configfs/sysfs enable attribute helpers

[Logan Gunthorpe]

On 2018-09-21 10:18 AM, Bjorn Helgaas wrote:
> Where do these store/show functions get connected to sysfs?  I know
> there's a lot of magic there, so apologies if I'm missing it.

Well in this patch set they are used in configfs not sysfs. It's not
magic, they are just helpers for other drivers. They are called in Patch
13 by NVMe target's configfs functions.

Logan

Re: [PATCH v6 06/13] PCI/P2PDMA: Add P2P DMA driver writer's documentation

[Bjorn Helgaas]

On Fri, Sep 21, 2018 at 12:03:12PM -0600, Logan Gunthorpe wrote:
> On 2018-09-21 10:41 AM, Bjorn Helgaas wrote:
> >> +away, the one returned will be chosen at random. This function returns the PCI
> > 
> > s/the one returned will be chosen at random/one will be chosen
> > arbitrarily/ ?  (I doubt it's really random)
> 
> You're the second person to ask this, but yes, we really do it randomly.
> Such that if there are multiple drivers getting resources they should be
> evenly distributed. It's not the ideal solution but if it were to do it
> arbitrarily then the code would likely return the same device all the
> time and any additional devices would not get used.

Ah, I see, I should have searched for "random" in that patch and answered
my own question :)  Sorry for the noise.

Bjorn

Re: [PATCH v6 03/13] PCI/P2PDMA: Add PCI p2pmem DMA mappings to adjust the bus offset

[Bjorn Helgaas]

On Fri, Sep 21, 2018 at 12:13:21PM -0600, Logan Gunthorpe wrote:
> On 2018-09-21 10:48 AM, Bjorn Helgaas wrote:
> >> I think the use of "map" in this context is slightly confusing because the
> >> general expectation is that map/unmap must be balanced.
> 
> Yeah, Jason said the same thing, but having an empty unmap function
> seems wasteful and Christoph said to just remove it. My opinion is that
> it's not that big an issue one way or another -- if we have to add an
> unmap later it's not really that hard.
> 
> >> If you keep "map", maybe add a sentence or two about why there's no
> >> corresponding unmap?
> 
> Will do.
> 
> > Another wrinkle is that "map" usually takes an A and gives you back a
> > B.  Now the caller has both A and B and both are still valid.
> > Here we pass in an SGL and the SGL is transformed, so the caller only
> > has B and A has been destroyed, i.e., the SGL can no longer be used as
> > it was before, and there's no way to get A back.
> 
> I wouldn't say that. Our map_sg function is doing the same thing
> dma_map_sg is: it sets the DMA address and length in the scatter list.
> So B is still A just with other fields set. If the caller wanted to map
> this SG in a different way they can still do so and the new DMA
> address/length would override the old values. (Normally, you'd want to
> unmap before doing something like that, but seeing our unmap is an empty
> operation, we wouldn't have to do that.)

Ok.  I was assuming s->dma_address would have been already set before
the call and would be overwritten by pci_p2pmem_map_sg().  But I guess
that's not the case -- sounds like s->dma_address is undefined before
the call.

Bjorn

Re: [PATCH v6 03/13] PCI/P2PDMA: Add PCI p2pmem DMA mappings to adjust the bus offset

[Logan Gunthorpe]

On 2018-09-21 2:00 PM, Bjorn Helgaas wrote:
> Ok.  I was assuming s->dma_address would have been already set before
> the call and would be overwritten by pci_p2pmem_map_sg().  But I guess
> that's not the case -- sounds like s->dma_address is undefined before
> the call.

Correct. It's set by whatever dma_map function operates on it.

Logan

Re: [PATCH v6 04/13] PCI/P2PDMA: Introduce configfs/sysfs enable attribute helpers

[Logan Gunthorpe]

On 2018-09-21 10:18 a.m., Bjorn Helgaas wrote:
> It'd be sort of nice if the contents of the sysfs file were valid
> things you could put *back* into it.  But it looks like the contents
> might be "none", which isn't valid for the store.  And the contents
> are never "on" or "off".

In fact, "none" would be accepted by strtobool() as a false (seeing it
starts with 'n' and strtobool() only looks at the first character).
However, per the rest of your feedback I've changed show() to report
"0", "1" or  pci_name() and dropped "auto". This matches what the other
strtobool configfs attributes are doing in NVMe target.

Logan

Re: [PATCH v6 04/13] PCI/P2PDMA: Introduce configfs/sysfs enable attribute helpers

[Bjorn Helgaas]

On Wed, Sep 12, 2018 at 06:11:47PM -0600, Logan Gunthorpe wrote:
> Users of the P2PDMA infrastructure will typically need a way for
> the user to tell the kernel to use P2P resources. Typically
> this will be a simple on/off boolean operation but sometimes
> it may be desirable for the user to specify the exact device to
> use for the P2P operation.
> 
> Add new helpers for attributes which take a boolean or a PCI device.
> Any boolean, or the word 'auto' turn P2P on or off. Specifying a full
> PCI device name/BDF will select the specific device.
> 
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>

I appreciate your update to drop "auto" and show 0/1/pci_name().
When you post that, include my:

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
>  drivers/pci/p2pdma.c       | 83 ++++++++++++++++++++++++++++++++++++++
>  include/linux/pci-p2pdma.h | 15 +++++++
>  2 files changed, 98 insertions(+)
> 
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 29bd40a87768..3da848f3fe72 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -9,6 +9,7 @@
>   */
>  
>  #define pr_fmt(fmt) "pci-p2pdma: " fmt
> +#include <linux/ctype.h>
>  #include <linux/pci-p2pdma.h>
>  #include <linux/module.h>
>  #include <linux/slab.h>
> @@ -856,3 +857,85 @@ int pci_p2pdma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
>  	return nents;
>  }
>  EXPORT_SYMBOL_GPL(pci_p2pdma_map_sg);
> +
> +/**
> + * pci_p2pdma_enable_store - parse a configfs/sysfs attribute store
> + *		to enable p2pdma
> + * @page: contents of the value to be stored
> + * @p2p_dev: returns the PCI device that was selected to be used
> + *		(if 'auto', 'none or a boolean isn't the store value)
> + * @use_p2pdma: returns whether to enable p2pdma or not
> + *
> + * Parses an attribute value to decide whether to enable p2pdma.
> + * The value can select a PCI device (using it's full BDF device
> + * name), a boolean, or 'auto'. 'auto' and a true boolean value
> + * have the same meaning. A false value disables p2pdma and
> + * a PCI device enables it to use a specific device as the
> + * backing provider.
> + *
> + * pci_p2pdma_enable_show() should be used as the show operation for
> + * the attribute.
> + *
> + * Returns 0 on success
> + */
> +int pci_p2pdma_enable_store(const char *page, struct pci_dev **p2p_dev,
> +			    bool *use_p2pdma)
> +{
> +	struct device *dev;
> +
> +	dev = bus_find_device_by_name(&pci_bus_type, NULL, page);
> +	if (dev) {
> +		*use_p2pdma = true;
> +		*p2p_dev = to_pci_dev(dev);
> +
> +		if (!pci_has_p2pmem(*p2p_dev)) {
> +			pr_err("PCI device has no peer-to-peer memory: %s\n",
> +			       page);
> +			pci_dev_put(*p2p_dev);
> +			return -ENODEV;
> +		}
> +
> +		return 0;
> +	} else if (sysfs_streq(page, "auto")) {
> +		*use_p2pdma = true;
> +		return 0;
> +	} else if ((page[0] == '0' || page[0] == '1') && !iscntrl(page[1])) {
> +		/*
> +		 * If the user enters a PCI device that  doesn't exist
> +		 * like "0000:01:00.1", we don't want strtobool to think
> +		 * it's a '0' when it's clearly not what the user wanted.
> +		 * So we require 0's and 1's to be exactly one character.
> +		 */
> +	} else if (!strtobool(page, use_p2pdma)) {
> +		return 0;
> +	}
> +
> +	pr_err("No such PCI device: %.*s\n", (int)strcspn(page, "\n"), page);
> +	return -ENODEV;
> +}
> +EXPORT_SYMBOL_GPL(pci_p2pdma_enable_store);
> +
> +/**
> + * pci_p2pdma_enable_show - show a configfs/sysfs attribute indicating
> + *		whether p2pdma is enabled
> + * @page: contents of the stored value
> + * @p2p_dev: the selected p2p device (NULL if no device is selected)
> + * @use_p2pdma: whether p2pdme has been enabled
> + *
> + * Attributes that use pci_p2pdma_enable_store() should use this function
> + * to show the value of the attribute.
> + *
> + * Returns 0 on success
> + */
> +ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
> +			       bool use_p2pdma)
> +{
> +	if (!use_p2pdma)
> +		return sprintf(page, "none\n");
> +
> +	if (!p2p_dev)
> +		return sprintf(page, "auto\n");
> +
> +	return sprintf(page, "%s\n", pci_name(p2p_dev));
> +}
> +EXPORT_SYMBOL_GPL(pci_p2pdma_enable_show);
> diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h
> index 2f03dbbf5af6..377de4d73767 100644
> --- a/include/linux/pci-p2pdma.h
> +++ b/include/linux/pci-p2pdma.h
> @@ -38,6 +38,10 @@ void pci_p2pmem_free_sgl(struct pci_dev *pdev, struct scatterlist *sgl);
>  void pci_p2pmem_publish(struct pci_dev *pdev, bool publish);
>  int pci_p2pdma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
>  		      enum dma_data_direction dir);
> +int pci_p2pdma_enable_store(const char *page, struct pci_dev **p2p_dev,
> +			    bool *use_p2pdma);
> +ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
> +			       bool use_p2pdma);
>  #else /* CONFIG_PCI_P2PDMA */
>  static inline int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar,
>  		size_t size, u64 offset)
> @@ -105,5 +109,16 @@ static inline int pci_p2pdma_map_sg(struct device *dev,
>  {
>  	return 0;
>  }
> +static inline int pci_p2pdma_enable_store(const char *page,
> +		struct pci_dev **p2p_dev, bool *use_p2pdma)
> +{
> +	*use_p2pdma = false;
> +	return 0;
> +}
> +static inline ssize_t pci_p2pdma_enable_show(char *page,
> +		struct pci_dev *p2p_dev, bool use_p2pdma)
> +{
> +	return sprintf(page, "none\n");
> +}
>  #endif /* CONFIG_PCI_P2PDMA */
>  #endif /* _LINUX_PCI_P2P_H */
> -- 
> 2.19.0
>