[PATCH v3 0/9] vfio/pci: Add mmap() for DMABUFs

[PATCH v3 0/9] vfio/pci: Add mmap() for DMABUFs

[Matt Evans]

Hi all,


This series is based on previous RFCs/discussions:

Tech topic: https://lore.kernel.org/linux-iommu/20250918214425.2677057-1-amastro@fb.com/
RFCv1:	    https://lore.kernel.org/all/20260226202211.929005-1-mattev@meta.com/
RFCv2:	    https://lore.kernel.org/kvm/20260312184613.3710705-1-mattev@meta.com/

The background/rationale is covered in more detail in the RFC cover
letters.  The TL;DR is:

The goal is to enable userspace driver designs that use VFIO to export
DMABUFs representing subsets of PCI device BARs, and "vend" those
buffers from a primary process to other subordinate processes by fd.
These processes then mmap() the buffers and their access to the device
is isolated to the exported ranges.  This is an improvement on sharing
the VFIO device fd to subordinate processes, which would allow
unfettered access.

This is achieved by enabling mmap() of vfio-pci DMABUFs, passed by fd
to subordinate processes.  Second, a new revocation mechanism is added
to allow the primary process to forcibly revoke access to
previously-shared BAR spans, even if the subordinate processes haven't
cleanly exited.

(The related topic of safe delegation of iommufd control to the
subordinate processes is not addressed here, and is follow-up work.)

As well as isolation and revocation, another advantage to accessing a
BAR through a VMA backed by a DMABUF is that it's straightforward to
mmap() the buffer with access attributes, such as write-combining.

Feedback from the RFCs requested that, instead of creating
DMABUF-specific vm_ops and .fault paths, to go the whole way and
migrate the existing VFIO PCI BAR mmap() to be backed by a DMABUF too,
resulting in a common vm_ops and fault handler for mmap()s of both the
VFIO device and explicitly-exported DMABUFs.  This will help future
iommufd emulation of VFIO Type1 peer-to-peer, making it easier to get
a DMABUF for a VFIO BAR as a DMA target.

mmap() conversion to use DMABUF underneath has been done for vfio-pci,
but not sub-drivers:

  nvgrace-gpu's mmap() override path is unchanged; I kept this out of
  scope for now not least because I don't have a thorough test setup
  for this system.  I would prefer to help the nvgrace-gpu maintainers
  enable BAR mmap() DMABUFs themselves.


Notes on patches
================


 PCI/P2PDMA: Add CONFIG_PCI_P2PDMA_CORE

   Later in the series, vfio-pci's mmap() is going to depend on
   pcim_p2pdma_provider() which depended on CONFIG_PCI_P2PDMA, which
   in turn depended on ZONE_DEVICE (which isn't available on 32-bit
   and some archs, because they lack MEMORY_HOTPLUG and friends).
   VFIO does _not_ require actual P2P to be present for basic mmap()
   functionality, only for the optional CONFIG_DMA_SHARED_BUFFER
   feature.

   This splits out p2pdma_core.c under CONFIG_PCI_P2PDMA_CORE (which
   currently contains pcim_p2pdma_provider()), and an optional
   CONFIG_PCI_P2PDMA which depends on ZONE_DEVICE etc. providing
   P2P functionality in the existing p2pdma.c.


 vfio/pci: Add a helper to look up PFNs for DMABUFs
 vfio/pci: Add a helper to create a DMABUF for a BAR-map VMA

   The first is for a DMABUF VMA fault handler to determine
   arbitrary-sized PFNs from ranges in DMABUF.  Secondly, refactor
   DMABUF export for use by the existing export feature and add a
   helper that creates a DMABUF corresponding to a VFIO BAR mmap()
   request.


 vfio/pci: Convert BAR mmap() to use a DMABUF

   The vfio-pci core mmap() creates a DMABUF with the helper, and the
   vm_ops fault handler uses the other helper to resolve the fault.
   Because this depends on DMABUF structs/code, CONFIG_VFIO_PCI_CORE
   needs to depend on CONFIG_DMA_SHARED_BUFFER.  The
   CONFIG_VFIO_PCI_DMABUF still conditionally enables the export
   support code.

   NOTE: The user mmap()s a device fd, but the resulting VMA's vm_file
   becomes that of the DMABUF.  The DMABUF takes ownership of the
   device and put()s it on release, which maintains the existing
   behaviour of a VMA keeping the VFIO device open.

   BAR zapping then happens via the existing vfio_pci_dma_buf_move()
   path, which now needs to unmap PTEs in the DMABUF's address_space.


 vfio/pci: Provide a user-facing name for BAR mappings

   There was a request for decent debug naming in /proc/<pid>/maps
   etc.  comparable to the existing VFIO names: since the VMAs are
   DMABUFs, they have a "dmabuf:" prefix and can't be 100% identical
   to before.  This is a user-visible change, but this patch at least
   now gives us extra info on the BDF & BAR being mapped.


 vfio/pci: Clean up BAR zap and revocation

   In general (see NOTE!) the vfio_pci_zap_bars() is now obsolete,
   since it unmaps PTEs in the VFIO device address_space which is now
   unused.  This consolidates all calls (e.g. around reset) with the
   neighbouring vfio_pci_dma_buf_move()s into new functions, to
   revoke-zap/unrevoke.  This makes the "revoke/un-revoke" steps
   clearer.

   NOTE: Because drivers can use their own vm_ops and override .mmap,
   the core must conservatively assume an overridden .mmap might still
   add PTEs to the VFIO device address_space and therefore still does
   the zap.  A new flag, zap_bars_on_revoke, enables the zap when
   .mmap is overridden.  A driver that does not need the zap can clear
   this to opt-out, e.g. if the driver calls down to the common mmap
   (and so uses DMABUFs).


 vfio/pci: Support mmap() of a VFIO DMABUF

   Adds mmap() for a DMABUF fd exported from vfio-pci.

   It was a goal to keep the VFIO device fd lifetime behaviour
   unchanged with respect to the DMABUFs.  An application can close
   all device fds, and this will revoke/clean up all DMABUFs; no
   mappings or other access can be performed now.  When enabling
   mmap() of the DMABUFs, this means access through the VMA is also
   revoked.  This complicates the fault handler because whilst the
   DMABUF exists, it has no guarantee that the corresponding VFIO
   device is still alive.  Adds synchronisation ensuring the vdev is
   available before vdev->memory_lock is touched; this holds the
   device registration so that even if the buffer has been cleaned up,
   vdev hasn't been freed and so the lock can be safely taken.

   This commit makes VFIO_PCI_CORE depend on PCI_P2PDMA_CORE (commit
   1) to bring in (only) the P2PDMA provider code.


 vfio/pci: Permanently revoke a DMABUF on request

   By weight, this is mostly a rename of revoked to an enum, status.
   There are now 3 states for a buffer, usable and revoked
   temporary/permanent.  A new VFIO feature is added,
   VFIO_DEVICE_FEATURE_DMA_BUF_REVOKE, which takes a DMABUF (exported
   from the same device) and permanently revokes it.  Thus a userspace
   driver can guarantee any downstream consumers of a shared fd are
   prevented from accessing a BAR range, and that range can be reused.
   NOTE: This might block userspace, waiting on importers to detach.

   The code doing revocation in vfio_pci_dma_buf_move() is moved,
   unchanged, to a common function for use by ..._move() and this new
   feature.


 vfio/pci: Add mmap() attributes to DMABUF feature

   Adds a new VFIO feature, VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR.
   After a DMABUF is exported, this feature is used to set a memory
   attribute that will be used by future mmap()s of the DMABUF fd.  It
   doesn't affect existing maps.

   The default is UC, and via the feature one can specify CPU access
   as WC.  The attribute is an enum/scalar rather than
   bitmap/cumulative.  The attributes follow a "try-fail" model where
   a client can request an attribute and either succeed or fail with
   ENOENT if it's unknown; if future attributes are platform-specific
   then their support can be probed.

   (Since it's just UC/WC for now, there is no reservation or numeric
   structure to the namespace yet, but we could support
   system/arch-specific values in future by carving out base +
   arch-specific + IMPDEF ranges.)


Testing
=======

(The [RFC ONLY] userspace test program, for QEMU edu-plus, can be
found in the GitHub branch below.  It at least illustrates how the
export, map, revoke, attribute, and close semantics interoperate.)

This code has been tested in mapping DMABUFs of single/multiple ranges
from multiple BARs, aliasing mmap()s, aliasing ranges across DMABUFs,
vm_pgoff > 0, revocation, shutdown/cleanup scenarios, and hugepage
mappings.  I've lightly tested WC mappings also (by observing
resulting PTEs as having the correct attributes...).  No regressions
observed on the VFIO selftests, or on our internal vfio-pci
applications.  VFIO on i386 has been build-tested.


End
===

This is based on VFIO next (e.g. at b9285405c5f6).

These commits are on GitHub for easier browsing, along with
"[RFC ONLY] selftests: vfio: Add standalone vfio_dmabuf_mmap_test":

https://github.com/metamev/linux/compare/b9285405c5f6...metamev:linux:dev/mev/vfio-dmabuf-mmap-v3


Thanks for reading,


Matt


================================================================================
Change log:

v3:
 - Refactor p2pdma.c: split out pcim_p2pdma_provider() into a new
   p2pdma_core.c under CONFIG_PCI_P2PDMA_CORE.

 - vfio_pci_dma_buf_find_pfn() cleanups: Rename parameter to priv,
   remove bad WARN, move unnecessary addition out of inner loop.

 - vfio_pci_core_mmap_prep_dmabuf() cleanups: Remove uint32_t, remove
   unnecessary const variable.

 - Conversion of BAR mmap() to DMABUF: VFIO_PCI_DMABUF depends on
   VFIO_PCI_CORE. vfio_pci_mmap_huge_fault(): move dev_dbg() outside
   of lock (argh), remove READ_ONCE(vdev)/move priv->vdev read and
   improve comment explanation.

 - On revoke, BAR zap defaults to on if .mmap is overridden by a
   driver (and implements an opt-out for the hisi_acc_vfio_pci driver,
   which overrides mmap() with a simple wrapper that ends up using the
   common DMABUF mmap() rather than custom mappings).

 - Reworded commit "vfio/pci: Support mmap() of a VFIO DMABUF" message
   for clarity.  Reworded vfio_pci_mmap_huge_fault() comment for
   accuracy (vdev validity depends on not being revoked).
   Added comment in mmap() explaining belt-and-braces approach for
   early detecting a map of a revoked buffer.

 - Revoke now uses VFIO_DEVICE_FEATURE_DMA_BUF rather than a new
   ioctl(); instead of the revoke helper taking 'revoked/permanently'
   bools, it's become vfio_pci_dma_buf_set_status() taking a single
   status enum.  Added a READ_ONCE() for the lockless test of
   priv->vdev (flags it as intentional, even if it's in practice going
   to be a single-copy atomic read).

 - Removed GET on vfio_pci_core_feature_dma_buf_memattr(), removed
   unnecessary taking of memory_lock, fixed error return values.  In
   particular, removes ENOTSUPP, and uses ENOENT to indicate an
   unknown attribute enum value was passed to SET.  In the discussion
   here,
   https://lore.kernel.org/all/20260602131417.41366391@shazbot.org/
   we'd agreed on EOPNOTSUPP before I realised that's already used
   elsewhere.  ENOENT uniquely indicates an unknown attribute.


v2:
https://lore.kernel.org/all/20260527102319.100128-1-mattev@meta.com/

 - Rebase on VFIO next, picking up Alex's
   vfio_pci_dma_buf_move()/vfio_pci_dma_buf_cleanup() fixes, and
   dropping "vfio/pci: Fix vfio_pci_dma_buf_cleanup() double-put"

 - Added "PCI/P2PDMA: Add CONFIG_PCI_P2PDMA_CORE" so that the
   newly-added vfio-pci hard dependency on the P2PDMA provider instead
   pulls in the _CORE variant and not the full-fat CONFIG_PCI_P2PDMA.
   This means that the core of vfio-pci does not need ZONE_DEVICE, but
   if it's available then enabling P2PDMA in turn enables DMABUF
   export.  Fixes basic VFIO operation on 32b or other platforms without
   ZONE_DEVICE.

 - Fixed comment inaccuracy in vfio_pci_dma_buf_revoke() and cleaned
   up vdev validity test.

 - vfio_pci_dma_buf_find_pfn(): use PAGE_ALIGN(), better span variable
   naming, OVF check

 - Made vm_pgoffs use consistent (keeping the resource index at the
   top and masking where offset is used).  For BAR mmap, use new
   vma_pgoff_adjust to create the DMABUF with the exact mmap()ed span
   instead of from the start of the BAR with an invisible portion
   before the mapping.

 - Added VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR to set memory attributes,
   instead of using the export `flags` field.

 - vfio_pci_ioctl_reset: Moved vfio_pci_zap_revoke_bars()
   (effectively, vfio_pci_dma_buf_move()) back after D0 transition.
   Note, if a BAR zap is needed, it's done in this function so now
   happens after this D0 transition with the _move; it was done before
   it at the time of the memory_lock taking.

 - Minimised vfio_pci_dma_buf_mmap() (removed redundant span check),
   added READ_ONCE for memattr

 - Misc fixes: comment in DMABUF name generation, removed superfluous
   READ_ONCE from faulthandler


v1:
https://lore.kernel.org/kvm/20260416131815.2729131-1-mattev@meta.com/

 - Cleanup of the common DMABUF-aware VMA vm_ops fault handler and
   export code.
 - Fixed a lot of races, particularly faults racing with DMABUF
   cleanup (if the VFIO device fds close, for example).
 - Added nicer human-readable names for VFIO mmap() VMAs


RFCv2:  Respin based on the feedback/suggestions:
https://lore.kernel.org/kvm/20260312184613.3710705-1-mattev@meta.com/

 - Transform the existing VFIO BAR mmap path to also use DMABUFs
   behind the scenes, and then simply share that code for
   explicitly-mapped DMABUFs.  Jason wanted to go that direction to
   enable iommufd VFIO type 1 emulation to pick up a DMABUF for an IO
   mapping.

 - Revoke buffers using a VFIO device fd ioctl

RFCv1:
https://lore.kernel.org/all/20260226202211.929005-1-mattev@meta.com/


Matt Evans (9):
  PCI/P2PDMA: Add CONFIG_PCI_P2PDMA_CORE
  vfio/pci: Add a helper to look up PFNs for DMABUFs
  vfio/pci: Add a helper to create a DMABUF for a BAR-map VMA
  vfio/pci: Convert BAR mmap() to use a DMABUF
  vfio/pci: Provide a user-facing name for BAR mappings
  vfio/pci: Clean up BAR zap and revocation
  vfio/pci: Support mmap() of a VFIO DMABUF
  vfio/pci: Permanently revoke a DMABUF on request
  vfio/pci: Add mmap() attributes to DMABUF feature

 MAINTAINERS                                   |   2 +-
 drivers/pci/Kconfig                           |  10 +-
 drivers/pci/Makefile                          |   1 +
 drivers/pci/p2pdma.c                          | 109 +---
 drivers/pci/p2pdma.h                          |  29 +
 drivers/pci/p2pdma_core.c                     | 118 ++++
 drivers/vfio/pci/Kconfig                      |   5 +-
 drivers/vfio/pci/Makefile                     |   3 +-
 .../vfio/pci/hisilicon/hisi_acc_vfio_pci.c    |   8 +
 drivers/vfio/pci/vfio_pci_config.c            |  30 +-
 drivers/vfio/pci/vfio_pci_core.c              | 213 +++++--
 drivers/vfio/pci/vfio_pci_dmabuf.c            | 564 +++++++++++++++---
 drivers/vfio/pci/vfio_pci_priv.h              |  64 +-
 include/linux/pci-p2pdma.h                    |  24 +-
 include/linux/pci.h                           |   2 +-
 include/linux/vfio_pci_core.h                 |   1 +
 include/uapi/linux/vfio.h                     |  47 ++
 17 files changed, 958 insertions(+), 272 deletions(-)
 create mode 100644 drivers/pci/p2pdma.h
 create mode 100644 drivers/pci/p2pdma_core.c

-- 
2.50.1 (Apple Git-155)

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

[Matt Evans]

The P2PDMA code currently provides two features under the same
CONFIG_PCI_P2PDMA option:

 1.  Locate providers via pcim_p2pdma_provider()
 2.  Manage actual P2P DMA

Some drivers (such as vfio-pci) depend on 1, without having a hard
dependency on 2.

A future commit expands the use of DMABUF in vfio-pci for non-P2P
scenarios, relying on pcim_p2pdma_provider() always being present.  If
that depended on CONFIG_PCI_P2PDMA, it would make vfio-pci only
available if CONFIG_ZONE_DEVICE is present (e.g. 64-bit systems), even
when P2P is not needed.

To resolve this, introduce CONFIG_PCI_P2PDMA_CORE and refactor the
basic provider functionality into a new p2pdma_core.c file.  This is
available even if the CONFIG_PCI_P2PDMA feature is disabled (or
unavailable due to !CONFIG_ZONE_DEVICE).  Then, drivers can enable any
additional P2P features with the original CONFIG_PCI_P2PDMA (available
when CONFIG_ZONE_DEVICE is set).

Signed-off-by: Matt Evans <matt@ozlabs.org>
---
 MAINTAINERS                |   2 +-
 drivers/pci/Kconfig        |  10 ++--
 drivers/pci/Makefile       |   1 +
 drivers/pci/p2pdma.c       | 109 ++--------------------------------
 drivers/pci/p2pdma.h       |  29 +++++++++
 drivers/pci/p2pdma_core.c  | 118 +++++++++++++++++++++++++++++++++++++
 include/linux/pci-p2pdma.h |  24 ++++----
 include/linux/pci.h        |   2 +-
 8 files changed, 174 insertions(+), 121 deletions(-)
 create mode 100644 drivers/pci/p2pdma.h
 create mode 100644 drivers/pci/p2pdma_core.c

diff --git a/MAINTAINERS b/MAINTAINERS
index c2c6d79275c6..b21523b3bd8b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -20617,7 +20617,7 @@ B:	https://bugzilla.kernel.org
 C:	irc://irc.oftc.net/linux-pci
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git
 F:	Documentation/driver-api/pci/p2pdma.rst
-F:	drivers/pci/p2pdma.c
+F:	drivers/pci/p2pdma*
 F:	include/linux/pci-p2pdma.h
 
 PCI POWER CONTROL
diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
index 33c88432b728..59d70bc84cc9 100644
--- a/drivers/pci/Kconfig
+++ b/drivers/pci/Kconfig
@@ -206,11 +206,7 @@ config PCIE_TPH
 config PCI_P2PDMA
 	bool "PCI peer-to-peer transfer support"
 	depends on ZONE_DEVICE
-	#
-	# The need for the scatterlist DMA bus address flag means PCI P2PDMA
-	# requires 64bit
-	#
-	depends on 64BIT
+	select PCI_P2PDMA_CORE
 	select GENERIC_ALLOCATOR
 	select NEED_SG_DMA_FLAGS
 	help
@@ -226,6 +222,10 @@ config PCI_P2PDMA
 
 	  If unsure, say N.
 
+config PCI_P2PDMA_CORE
+	default n
+	bool
+
 config PCI_LABEL
 	def_bool y if (DMI || ACPI)
 	select NLS
diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile
index 41ebc3b9a518..0b32572d57a1 100644
--- a/drivers/pci/Makefile
+++ b/drivers/pci/Makefile
@@ -30,6 +30,7 @@ obj-$(CONFIG_PCI_SYSCALL)	+= syscall.o
 obj-$(CONFIG_PCI_STUB)		+= pci-stub.o
 obj-$(CONFIG_PCI_PF_STUB)	+= pci-pf-stub.o
 obj-$(CONFIG_PCI_ECAM)		+= ecam.o
+obj-$(CONFIG_PCI_P2PDMA_CORE)	+= p2pdma_core.o
 obj-$(CONFIG_PCI_P2PDMA)	+= p2pdma.o
 obj-$(CONFIG_XEN_PCIDEV_FRONTEND) += xen-pcifront.o
 obj-$(CONFIG_VGA_ARB)		+= vgaarb.o
diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 7c898542af8d..50b1a7daf55c 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -21,12 +21,7 @@
 #include <linux/seq_buf.h>
 #include <linux/xarray.h>
 
-struct pci_p2pdma {
-	struct gen_pool *pool;
-	bool p2pmem_published;
-	struct xarray map_types;
-	struct p2pdma_provider mem[PCI_STD_NUM_BARS];
-};
+#include "p2pdma.h"
 
 struct pci_p2pdma_pagemap {
 	struct dev_pagemap pgmap;
@@ -226,110 +221,16 @@ static const struct dev_pagemap_ops p2pdma_pgmap_ops = {
 	.folio_free = p2pdma_folio_free,
 };
 
-static void pci_p2pdma_release(void *data)
+void pci_p2pdma_release_pool(struct pci_dev *pdev, struct pci_p2pdma *p2pdma)
 {
-	struct pci_dev *pdev = data;
-	struct pci_p2pdma *p2pdma;
-
-	p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
-	if (!p2pdma)
-		return;
-
-	/* Flush and disable pci_alloc_p2p_mem() */
-	pdev->p2pdma = NULL;
-	if (p2pdma->pool)
-		synchronize_rcu();
-	xa_destroy(&p2pdma->map_types);
-
 	if (!p2pdma->pool)
 		return;
 
+	synchronize_rcu();
 	gen_pool_destroy(p2pdma->pool);
 	sysfs_remove_group(&pdev->dev.kobj, &p2pmem_group);
 }
 
-/**
- * pcim_p2pdma_init - Initialise peer-to-peer DMA providers
- * @pdev: The PCI device to enable P2PDMA for
- *
- * This function initializes the peer-to-peer DMA infrastructure
- * for a PCI device. It allocates and sets up the necessary data
- * structures to support P2PDMA operations, including mapping type
- * tracking.
- */
-int pcim_p2pdma_init(struct pci_dev *pdev)
-{
-	struct pci_p2pdma *p2p;
-	int i, ret;
-
-	p2p = rcu_dereference_protected(pdev->p2pdma, 1);
-	if (p2p)
-		return 0;
-
-	p2p = devm_kzalloc(&pdev->dev, sizeof(*p2p), GFP_KERNEL);
-	if (!p2p)
-		return -ENOMEM;
-
-	xa_init(&p2p->map_types);
-	/*
-	 * Iterate over all standard PCI BARs and record only those that
-	 * correspond to MMIO regions. Skip non-memory resources (e.g. I/O
-	 * port BARs) since they cannot be used for peer-to-peer (P2P)
-	 * transactions.
-	 */
-	for (i = 0; i < PCI_STD_NUM_BARS; i++) {
-		if (!(pci_resource_flags(pdev, i) & IORESOURCE_MEM))
-			continue;
-
-		p2p->mem[i].owner = &pdev->dev;
-		p2p->mem[i].bus_offset =
-			pci_bus_address(pdev, i) - pci_resource_start(pdev, i);
-	}
-
-	ret = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_release, pdev);
-	if (ret)
-		goto out_p2p;
-
-	rcu_assign_pointer(pdev->p2pdma, p2p);
-	return 0;
-
-out_p2p:
-	devm_kfree(&pdev->dev, p2p);
-	return ret;
-}
-EXPORT_SYMBOL_GPL(pcim_p2pdma_init);
-
-/**
- * pcim_p2pdma_provider - Get peer-to-peer DMA provider
- * @pdev: The PCI device to enable P2PDMA for
- * @bar: BAR index to get provider
- *
- * This function gets peer-to-peer DMA provider for a PCI device. The lifetime
- * of the provider (and of course the MMIO) is bound to the lifetime of the
- * driver. A driver calling this function must ensure that all references to the
- * provider, and any DMA mappings created for any MMIO, are all cleaned up
- * before the driver remove() completes.
- *
- * Since P2P is almost always shared with a second driver this means some system
- * to notify, invalidate and revoke the MMIO's DMA must be in place to use this
- * function. For example a revoke can be built using DMABUF.
- */
-struct p2pdma_provider *pcim_p2pdma_provider(struct pci_dev *pdev, int bar)
-{
-	struct pci_p2pdma *p2p;
-
-	if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))
-		return NULL;
-
-	p2p = rcu_dereference_protected(pdev->p2pdma, 1);
-	if (WARN_ON(!p2p))
-		/* Someone forgot to call to pcim_p2pdma_init() before */
-		return NULL;
-
-	return &p2p->mem[bar];
-}
-EXPORT_SYMBOL_GPL(pcim_p2pdma_provider);
-
 static int pci_p2pdma_setup_pool(struct pci_dev *pdev)
 {
 	struct pci_p2pdma *p2pdma;
@@ -932,8 +833,8 @@ void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size)
 	struct pci_p2pdma *p2pdma;
 
 	/*
-	 * Pairs with synchronize_rcu() in pci_p2pdma_release() to
-	 * ensure pdev->p2pdma is non-NULL for the duration of the
+	 * Pairs with synchronize_rcu() in pci_p2pdma_release_pool()
+	 * to ensure pdev->p2pdma is non-NULL for the duration of the
 	 * read-lock.
 	 */
 	rcu_read_lock();
diff --git a/drivers/pci/p2pdma.h b/drivers/pci/p2pdma.h
new file mode 100644
index 000000000000..453f4aa7ade8
--- /dev/null
+++ b/drivers/pci/p2pdma.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * PCI Peer 2 Peer DMA support.
+ */
+
+#ifndef _PCI_P2PDMA_H
+#define _PCI_P2PDMA_H
+
+#include <linux/genalloc.h>
+#include <linux/pci-p2pdma.h>
+#include <linux/xarray.h>
+
+struct pci_p2pdma {
+	struct gen_pool *pool;
+	bool p2pmem_published;
+	struct xarray map_types;
+	struct p2pdma_provider mem[PCI_STD_NUM_BARS];
+};
+
+#ifdef CONFIG_PCI_P2PDMA
+void pci_p2pdma_release_pool(struct pci_dev *pdev, struct pci_p2pdma *p2pdma);
+#else
+static inline void pci_p2pdma_release_pool(struct pci_dev *pdev, struct pci_p2pdma *p2pdma)
+{
+}
+#endif
+
+#endif
+
diff --git a/drivers/pci/p2pdma_core.c b/drivers/pci/p2pdma_core.c
new file mode 100644
index 000000000000..1fda15d40196
--- /dev/null
+++ b/drivers/pci/p2pdma_core.c
@@ -0,0 +1,118 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * PCI Peer 2 Peer DMA support core, providing a bare-bones
+ * pcim_p2pdma_provider() interface to drivers even if full P2PDMA
+ * isn't present.  The full P2PDMA feature is in p2pdma.c (see
+ * CONFIG_PCI_P2PDMA).
+ *
+ * Copyright (c) 2016-2018, Logan Gunthorpe
+ * Copyright (c) 2016-2017, Microsemi Corporation
+ * Copyright (c) 2017, Christoph Hellwig
+ * Copyright (c) 2018, Eideticom Inc.
+ */
+
+#define pr_fmt(fmt) "pci-p2pdma: " fmt
+#include <linux/ctype.h>
+#include <linux/genalloc.h>
+#include <linux/memremap.h>
+#include <linux/pci-p2pdma.h>
+#include <linux/xarray.h>
+
+#include "p2pdma.h"
+
+static void pci_p2pdma_release(void *data)
+{
+	struct pci_dev *pdev = data;
+	struct pci_p2pdma *p2pdma;
+
+	p2pdma = rcu_dereference_protected(pdev->p2pdma, 1);
+	if (!p2pdma)
+		return;
+
+	/* Flush and disable pci_alloc_p2p_mem() */
+	pdev->p2pdma = NULL;
+	pci_p2pdma_release_pool(pdev, p2pdma);
+	xa_destroy(&p2pdma->map_types);
+}
+
+/**
+ * pcim_p2pdma_init - Initialise peer-to-peer DMA providers
+ * @pdev: The PCI device to enable P2PDMA for
+ *
+ * This function initializes the peer-to-peer DMA infrastructure
+ * for a PCI device. It allocates and sets up the necessary data
+ * structures to support P2PDMA operations, including mapping type
+ * tracking.
+ */
+int pcim_p2pdma_init(struct pci_dev *pdev)
+{
+	struct pci_p2pdma *p2p;
+	int i, ret;
+
+	p2p = rcu_dereference_protected(pdev->p2pdma, 1);
+	if (p2p)
+		return 0;
+
+	p2p = devm_kzalloc(&pdev->dev, sizeof(*p2p), GFP_KERNEL);
+	if (!p2p)
+		return -ENOMEM;
+
+	xa_init(&p2p->map_types);
+	/*
+	 * Iterate over all standard PCI BARs and record only those that
+	 * correspond to MMIO regions. Skip non-memory resources (e.g. I/O
+	 * port BARs) since they cannot be used for peer-to-peer (P2P)
+	 * transactions.
+	 */
+	for (i = 0; i < PCI_STD_NUM_BARS; i++) {
+		if (!(pci_resource_flags(pdev, i) & IORESOURCE_MEM))
+			continue;
+
+		p2p->mem[i].owner = &pdev->dev;
+		p2p->mem[i].bus_offset =
+			pci_bus_address(pdev, i) - pci_resource_start(pdev, i);
+	}
+
+	ret = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_release, pdev);
+	if (ret)
+		goto out_p2p;
+
+	rcu_assign_pointer(pdev->p2pdma, p2p);
+	return 0;
+
+out_p2p:
+	devm_kfree(&pdev->dev, p2p);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(pcim_p2pdma_init);
+
+/**
+ * pcim_p2pdma_provider - Get peer-to-peer DMA provider
+ * @pdev: The PCI device to enable P2PDMA for
+ * @bar: BAR index to get provider
+ *
+ * This function gets peer-to-peer DMA provider for a PCI device. The lifetime
+ * of the provider (and of course the MMIO) is bound to the lifetime of the
+ * driver. A driver calling this function must ensure that all references to the
+ * provider, and any DMA mappings created for any MMIO, are all cleaned up
+ * before the driver remove() completes.
+ *
+ * Since P2P is almost always shared with a second driver this means some system
+ * to notify, invalidate and revoke the MMIO's DMA must be in place to use this
+ * function. For example a revoke can be built using DMABUF.
+ */
+struct p2pdma_provider *pcim_p2pdma_provider(struct pci_dev *pdev, int bar)
+{
+	struct pci_p2pdma *p2p;
+
+	if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))
+		return NULL;
+
+	p2p = rcu_dereference_protected(pdev->p2pdma, 1);
+	if (WARN_ON(!p2p))
+		/* Someone forgot to call to pcim_p2pdma_init() before */
+		return NULL;
+
+	return &p2p->mem[bar];
+}
+EXPORT_SYMBOL_GPL(pcim_p2pdma_provider);
diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h
index 873de20a2247..4c42a7b2ee85 100644
--- a/include/linux/pci-p2pdma.h
+++ b/include/linux/pci-p2pdma.h
@@ -67,9 +67,22 @@ enum pci_p2pdma_map_type {
 	PCI_P2PDMA_MAP_THRU_HOST_BRIDGE,
 };
 
-#ifdef CONFIG_PCI_P2PDMA
+#ifdef CONFIG_PCI_P2PDMA_CORE
 int pcim_p2pdma_init(struct pci_dev *pdev);
 struct p2pdma_provider *pcim_p2pdma_provider(struct pci_dev *pdev, int bar);
+#else
+static inline int pcim_p2pdma_init(struct pci_dev *pdev)
+{
+	return -EOPNOTSUPP;
+}
+static inline struct p2pdma_provider *pcim_p2pdma_provider(struct pci_dev *pdev,
+							   int bar)
+{
+	return NULL;
+}
+#endif
+
+#ifdef CONFIG_PCI_P2PDMA
 int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
 		u64 offset);
 int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,
@@ -89,15 +102,6 @@ ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
 enum pci_p2pdma_map_type pci_p2pdma_map_type(struct p2pdma_provider *provider,
 					     struct device *dev);
 #else /* CONFIG_PCI_P2PDMA */
-static inline int pcim_p2pdma_init(struct pci_dev *pdev)
-{
-	return -EOPNOTSUPP;
-}
-static inline struct p2pdma_provider *pcim_p2pdma_provider(struct pci_dev *pdev,
-							   int bar)
-{
-	return NULL;
-}
 static inline int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar,
 		size_t size, u64 offset)
 {
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 2c4454583c11..531aec355686 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -557,7 +557,7 @@ struct pci_dev {
 	u16		pasid_cap;	/* PASID Capability offset */
 	u16		pasid_features;
 #endif
-#ifdef CONFIG_PCI_P2PDMA
+#ifdef CONFIG_PCI_P2PDMA_CORE
 	struct pci_p2pdma __rcu *p2pdma;
 #endif
 #ifdef CONFIG_PCI_DOE
-- 
2.50.1 (Apple Git-155)

[PATCH v3 2/9] vfio/pci: Add a helper to look up PFNs for DMABUFs

[Matt Evans]

Add vfio_pci_dma_buf_find_pfn(), which a VMA fault handler can use to
find a PFN.

This supports multi-range DMABUFs, which typically would be used to
represent scattered spans but might even represent overlapping or
aliasing spans of PFNs.

Because this is intended to be used in vfio_pci_core.c, we also need
to expose the struct vfio_pci_dma_buf in the vfio_pci_priv.h header.

Signed-off-by: Matt Evans <matt@ozlabs.org>
---
 drivers/vfio/pci/vfio_pci_dmabuf.c | 137 ++++++++++++++++++++++++++---
 drivers/vfio/pci/vfio_pci_priv.h   |  20 +++++
 2 files changed, 144 insertions(+), 13 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index c16f460c01d6..9e5e865f6fb6 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -9,19 +9,6 @@
 
 MODULE_IMPORT_NS("DMA_BUF");
 
-struct vfio_pci_dma_buf {
-	struct dma_buf *dmabuf;
-	struct vfio_pci_core_device *vdev;
-	struct list_head dmabufs_elm;
-	size_t size;
-	struct phys_vec *phys_vec;
-	struct p2pdma_provider *provider;
-	u32 nr_ranges;
-	struct kref kref;
-	struct completion comp;
-	u8 revoked : 1;
-};
-
 static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
 				   struct dma_buf_attachment *attachment)
 {
@@ -106,6 +93,130 @@ static const struct dma_buf_ops vfio_pci_dmabuf_ops = {
 	.release = vfio_pci_dma_buf_release,
 };
 
+int vfio_pci_dma_buf_find_pfn(struct vfio_pci_dma_buf *priv,
+			      struct vm_area_struct *vma,
+			      unsigned long address,
+			      unsigned int order,
+			      unsigned long *out_pfn)
+{
+	/*
+	 * Given a VMA (start, end, pgoffs) and a fault address,
+	 * search the corresponding DMABUF's phys_vec[] to find the
+	 * range representing the address's offset into the VMA, and
+	 * its PFN.
+	 *
+	 * The phys_vec[] ranges represent contiguous spans of VAs
+	 * upwards from the buffer offset 0; the actual PFNs might be
+	 * in any order, overlap/alias, etc.  Calculate an offset of
+	 * the desired page given VMA start/pgoff and address, then
+	 * search upwards from 0 to find which span contains it.
+	 *
+	 * On success, a valid PFN for a page sized by 'order' is
+	 * returned into out_pfn.
+	 *
+	 * Failure occurs if:
+	 * - The page would cross the edge of the VMA
+	 * - The page isn't entirely contained within a range
+	 * - We find a range, but the final PFN isn't aligned to the
+	 *   requested order.
+	 *
+	 * (Upon failure, the caller is expected to try again with a
+	 * smaller order; the tests above will always succeed for
+	 * order=0 as the limit case.)
+	 *
+	 * It's suboptimal if DMABUFs are created with neigbouring
+	 * ranges that are physically contiguous, since hugepages
+	 * can't straddle range boundaries.  (The construction of the
+	 * ranges vector should merge such ranges.)
+	 *
+	 * Finally, vma_pgoff_adjust is used for a DMABUF representing
+	 * a VFIO BAR mmap, which is created from the start of the
+	 * offset region.
+	 */
+
+	const unsigned long pagesize = PAGE_SIZE << order;
+	unsigned long vma_off = ((vma->vm_pgoff - priv->vma_pgoff_adjust) <<
+				 PAGE_SHIFT) & VFIO_PCI_OFFSET_MASK;
+	unsigned long rounded_page_addr = ALIGN_DOWN(address, pagesize);
+	unsigned long rounded_page_end = rounded_page_addr + pagesize;
+	unsigned long page_buf_offset;
+	unsigned long page_buf_offset_end;
+	unsigned long range_buf_offset = 0;
+	unsigned int i;
+
+	if (rounded_page_addr < vma->vm_start || rounded_page_end > vma->vm_end) {
+		if (order > 0)
+			return -EAGAIN;
+
+		/* A fault address outside of the VMA is absurd. */
+		WARN(1, "Fault addr 0x%lx outside VMA 0x%lx-0x%lx\n",
+		     address, vma->vm_start, vma->vm_end);
+		return -EFAULT;
+	}
+
+	/*
+	 * page_buff_offset[_end] is the span of DMABUF offsets
+	 * corresponding to the faulting page:
+	 */
+	if (unlikely(check_add_overflow(rounded_page_addr - vma->vm_start,
+					vma_off, &page_buf_offset) ||
+		     check_add_overflow(page_buf_offset, pagesize,
+					&page_buf_offset_end)))
+		return -EFAULT;
+
+	for (i = 0; i < priv->nr_ranges; i++) {
+		size_t range_len = priv->phys_vec[i].len;
+		phys_addr_t range_start = priv->phys_vec[i].paddr;
+
+		/*
+		 * If the current range starts after the page's span,
+		 * this and any future range won't match.  Bail early.
+		 */
+		if (page_buf_offset_end <= range_buf_offset)
+			break;
+
+		if (page_buf_offset >= range_buf_offset &&
+		    page_buf_offset_end <= range_buf_offset + range_len) {
+			/*
+			 * The faulting page is wholly contained
+			 * within the span represented by the range.
+			 * Validate PFN alignment for the order:
+			 */
+			unsigned long pfn = (range_start + page_buf_offset -
+					     range_buf_offset) / PAGE_SIZE;
+
+			if (IS_ALIGNED(pfn, 1 << order)) {
+				*out_pfn = pfn;
+				return 0;
+			}
+			/* Retry with smaller order */
+			return -EAGAIN;
+		}
+		range_buf_offset += range_len;
+	}
+
+	/*
+	 * A hugepage straddling a range boundary will fail to match a
+	 * range, but the address will (eventually) match when retried
+	 * with a smaller page.
+	 */
+	if (order > 0)
+		return -EAGAIN;
+
+	/*
+	 * If we get here, the address fell outside of the span
+	 * represented by the (concatenated) ranges.  Setup of a
+	 * mapping must ensure that the VMA is <= the total size of
+	 * the ranges, so this should never happen.  But, if it does,
+	 * force SIGBUS for the access and warn.
+	 */
+	WARN_ONCE(1, "No range for addr 0x%lx, order %d: VMA 0x%lx-0x%lx pgoff 0x%lx, %u ranges, size 0x%zx\n",
+		  address, order, vma->vm_start, vma->vm_end, vma->vm_pgoff,
+		  priv->nr_ranges, priv->size);
+
+	return -EFAULT;
+}
+
 /*
  * This is a temporary "private interconnect" between VFIO DMABUF and iommufd.
  * It allows the two co-operating drivers to exchange the physical address of
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index fca9d0dfac90..c8f6f959056a 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -23,6 +23,20 @@ struct vfio_pci_ioeventfd {
 	bool			test_mem;
 };
 
+struct vfio_pci_dma_buf {
+	struct dma_buf *dmabuf;
+	struct vfio_pci_core_device *vdev;
+	struct list_head dmabufs_elm;
+	size_t size;
+	struct phys_vec *phys_vec;
+	struct p2pdma_provider *provider;
+	u32 nr_ranges;
+	struct kref kref;
+	struct completion comp;
+	unsigned long vma_pgoff_adjust;
+	u8 revoked : 1;
+};
+
 bool vfio_pci_intx_mask(struct vfio_pci_core_device *vdev);
 void vfio_pci_intx_unmask(struct vfio_pci_core_device *vdev);
 
@@ -114,6 +128,12 @@ static inline bool vfio_pci_is_vga(struct pci_dev *pdev)
 	return (pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA;
 }
 
+int vfio_pci_dma_buf_find_pfn(struct vfio_pci_dma_buf *vpdmabuf,
+			      struct vm_area_struct *vma,
+			      unsigned long address,
+			      unsigned int order,
+			      unsigned long *out_pfn);
+
 #ifdef CONFIG_VFIO_PCI_DMABUF
 int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 				  struct vfio_device_feature_dma_buf __user *arg,
-- 
2.50.1 (Apple Git-155)

[PATCH v3 3/9] vfio/pci: Add a helper to create a DMABUF for a BAR-map VMA

[Matt Evans]

This helper, vfio_pci_core_mmap_prep_dmabuf(), creates a single-range
DMABUF for the purpose of mapping a PCI BAR.  This is used in a future
commit by VFIO's ordinary mmap() path.

This function transfers ownership of the VFIO device fd to the
DMABUF, which fput()s when it's released.

Refactor the existing vfio_pci_core_feature_dma_buf() to split out
export code common to the two paths, VFIO_DEVICE_FEATURE_DMA_BUF and
this new VFIO_BAR mmap().

Signed-off-by: Matt Evans <matt@ozlabs.org>
---
 drivers/vfio/pci/vfio_pci_dmabuf.c | 142 +++++++++++++++++++++++------
 drivers/vfio/pci/vfio_pci_priv.h   |   5 +
 2 files changed, 117 insertions(+), 30 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index 9e5e865f6fb6..21180acf9600 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -82,6 +82,8 @@ static void vfio_pci_dma_buf_release(struct dma_buf *dmabuf)
 		up_write(&priv->vdev->memory_lock);
 		vfio_device_put_registration(&priv->vdev->vdev);
 	}
+	if (priv->vfile)
+		fput(priv->vfile);
 	kfree(priv->phys_vec);
 	kfree(priv);
 }
@@ -217,6 +219,45 @@ int vfio_pci_dma_buf_find_pfn(struct vfio_pci_dma_buf *priv,
 	return -EFAULT;
 }
 
+/*
+ * Create a DMABUF corresponding to priv, add it to vdev->dmabufs list
+ * for tracking (meaning cleanup or revocation will zap it), and take
+ * a vfio_device registration.
+ */
+static int vfio_pci_dmabuf_export(struct vfio_pci_core_device *vdev,
+				  struct vfio_pci_dma_buf *priv, u32 flags)
+{
+	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+
+	if (!vfio_device_try_get_registration(&vdev->vdev))
+		return -ENODEV;
+
+	exp_info.ops = &vfio_pci_dmabuf_ops;
+	exp_info.size = priv->size;
+	exp_info.flags = flags;
+	exp_info.priv = priv;
+
+	priv->dmabuf = dma_buf_export(&exp_info);
+	if (IS_ERR(priv->dmabuf)) {
+		vfio_device_put_registration(&vdev->vdev);
+		return PTR_ERR(priv->dmabuf);
+	}
+
+	kref_init(&priv->kref);
+	init_completion(&priv->comp);
+
+	/* dma_buf_put() now frees priv */
+	INIT_LIST_HEAD(&priv->dmabufs_elm);
+	down_write(&vdev->memory_lock);
+	dma_resv_lock(priv->dmabuf->resv, NULL);
+	priv->revoked = !__vfio_pci_memory_enabled(vdev);
+	list_add_tail(&priv->dmabufs_elm, &vdev->dmabufs);
+	dma_resv_unlock(priv->dmabuf->resv);
+	up_write(&vdev->memory_lock);
+
+	return 0;
+}
+
 /*
  * This is a temporary "private interconnect" between VFIO DMABUF and iommufd.
  * It allows the two co-operating drivers to exchange the physical address of
@@ -335,7 +376,6 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 {
 	struct vfio_device_feature_dma_buf get_dma_buf = {};
 	struct vfio_region_dma_range *dma_ranges;
-	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
 	struct vfio_pci_dma_buf *priv;
 	size_t length;
 	int ret;
@@ -395,34 +435,9 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 	kfree(dma_ranges);
 	dma_ranges = NULL;
 
-	if (!vfio_device_try_get_registration(&vdev->vdev)) {
-		ret = -ENODEV;
+	ret = vfio_pci_dmabuf_export(vdev, priv, get_dma_buf.open_flags);
+	if (ret)
 		goto err_free_phys;
-	}
-
-	exp_info.ops = &vfio_pci_dmabuf_ops;
-	exp_info.size = priv->size;
-	exp_info.flags = get_dma_buf.open_flags;
-	exp_info.priv = priv;
-
-	priv->dmabuf = dma_buf_export(&exp_info);
-	if (IS_ERR(priv->dmabuf)) {
-		ret = PTR_ERR(priv->dmabuf);
-		goto err_dev_put;
-	}
-
-	kref_init(&priv->kref);
-	init_completion(&priv->comp);
-
-	/* dma_buf_put() now frees priv */
-	INIT_LIST_HEAD(&priv->dmabufs_elm);
-	down_write(&vdev->memory_lock);
-	dma_resv_lock(priv->dmabuf->resv, NULL);
-	priv->revoked = !__vfio_pci_memory_enabled(vdev);
-	list_add_tail(&priv->dmabufs_elm, &vdev->dmabufs);
-	dma_resv_unlock(priv->dmabuf->resv);
-	up_write(&vdev->memory_lock);
-
 	/*
 	 * dma_buf_fd() consumes the reference, when the file closes the dmabuf
 	 * will be released.
@@ -433,8 +448,6 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 
 	return ret;
 
-err_dev_put:
-	vfio_device_put_registration(&vdev->vdev);
 err_free_phys:
 	kfree(priv->phys_vec);
 err_free_priv:
@@ -444,6 +457,75 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 	return ret;
 }
 
+int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
+				   struct vm_area_struct *vma,
+				   u64 phys_start, u64 req_len,
+				   unsigned int res_index)
+{
+	struct vfio_pci_dma_buf *priv;
+	unsigned long vma_pgoff = vma->vm_pgoff & (VFIO_PCI_OFFSET_MASK >> PAGE_SHIFT);
+	int ret;
+
+	priv = kzalloc_obj(*priv);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->phys_vec = kzalloc_obj(*priv->phys_vec);
+	if (!priv->phys_vec) {
+		ret = -ENOMEM;
+		goto err_free_priv;
+	}
+
+	/*
+	 * The DMABUF begins from the mmap()'s BAR offset, i.e. the
+	 * start of the VMA corresponds to byte 0 of the DMABUF and
+	 * byte (vma_pgoff << PAGE_SHIFT) of the BAR.
+	 *
+	 * vfio_pci_dma_buf_find_pfn() reverses this offset using
+	 * vma_pgoff_adjust, so that ultimately a fault's offset from
+	 * the start of the _VMA_ has a consistent usage whether the
+	 * VMA originates from an mmap() of the VFIO device here or a
+	 * direct DMABUF mmap().
+	 */
+	priv->vdev = vdev;
+	priv->size = req_len;
+	priv->nr_ranges = 1;
+	priv->vma_pgoff_adjust = vma_pgoff;
+	priv->provider = pcim_p2pdma_provider(vdev->pdev, res_index);
+	if (!priv->provider) {
+		ret = -EINVAL;
+		goto err_free_phys;
+	}
+
+	priv->phys_vec[0].paddr = phys_start + ((u64)vma_pgoff << PAGE_SHIFT);
+	priv->phys_vec[0].len = priv->size;
+
+	ret = vfio_pci_dmabuf_export(vdev, priv, O_CLOEXEC | O_RDWR);
+	if (ret)
+		goto err_free_phys;
+
+	/*
+	 * Ownership of the DMABUF file transfers to the VMA so that
+	 * other users can locate the DMABUF via a VA.  Ownership of
+	 * the original VFIO device file being mmap()ed transfers to
+	 * priv, and is put when the DMABUF is released.  This
+	 * intentionally does not use get_file()/vma_set_file()
+	 * because the references are already held, and ownership
+	 * moves.
+	 */
+	priv->vfile = vma->vm_file;
+	vma->vm_file = priv->dmabuf->file;
+	vma->vm_private_data = priv;
+
+	return 0;
+
+err_free_phys:
+	kfree(priv->phys_vec);
+err_free_priv:
+	kfree(priv);
+	return ret;
+}
+
 void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
 {
 	struct vfio_pci_dma_buf *priv;
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index c8f6f959056a..06dc0fd3e230 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -30,6 +30,7 @@ struct vfio_pci_dma_buf {
 	size_t size;
 	struct phys_vec *phys_vec;
 	struct p2pdma_provider *provider;
+	struct file *vfile;
 	u32 nr_ranges;
 	struct kref kref;
 	struct completion comp;
@@ -133,6 +134,10 @@ int vfio_pci_dma_buf_find_pfn(struct vfio_pci_dma_buf *vpdmabuf,
 			      unsigned long address,
 			      unsigned int order,
 			      unsigned long *out_pfn);
+int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
+				   struct vm_area_struct *vma,
+				   u64 phys_start, u64 req_len,
+				   unsigned int res_index);
 
 #ifdef CONFIG_VFIO_PCI_DMABUF
 int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
-- 
2.50.1 (Apple Git-155)

[PATCH v3 4/9] vfio/pci: Convert BAR mmap() to use a DMABUF

[Matt Evans]

Convert the VFIO device fd fops->mmap to create a DMABUF representing
the BAR mapping, and make the VMA fault handler look up PFNs from the
corresponding DMABUF.  This supports future code mmap()ing BAR
DMABUFs, and iommufd work to support Type1 P2P.

First, vfio_pci_core_mmap() uses the new
vfio_pci_core_mmap_prep_dmabuf() helper to export a DMABUF
representing a single BAR range.  Then, the vfio_pci_mmap_huge_fault()
callback is updated to understand revoked buffers, and uses the new
vfio_pci_dma_buf_find_pfn() helper to determine the PFN for a given
fault address.

Now that the VFIO DMABUFs can be mmap()ed, vfio_pci_dma_buf_move()
zaps PTEs (used on the revocation and cleanup paths).

CONFIG_VFIO_PCI_CORE now unconditionally depends on
CONFIG_DMA_SHARED_BUFFER and CONFIG_PCI_P2PDMA_CORE.  The
CONFIG_VFIO_PCI_DMABUF feature conditionally includes support for
VFIO_DEVICE_FEATURE_DMA_BUF, depending on the availability of
CONFIG_PCI_P2PDMA.

Signed-off-by: Matt Evans <matt@ozlabs.org>
---
 drivers/vfio/pci/Kconfig           |  5 +-
 drivers/vfio/pci/Makefile          |  3 +-
 drivers/vfio/pci/vfio_pci_core.c   | 75 +++++++++++++++++++-----------
 drivers/vfio/pci/vfio_pci_dmabuf.c | 12 +++++
 drivers/vfio/pci/vfio_pci_priv.h   | 11 +----
 5 files changed, 67 insertions(+), 39 deletions(-)

diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
index 296bf01e185e..67a2ae1fbc04 100644
--- a/drivers/vfio/pci/Kconfig
+++ b/drivers/vfio/pci/Kconfig
@@ -6,6 +6,8 @@ config VFIO_PCI_CORE
 	tristate
 	select VFIO_VIRQFD
 	select IRQ_BYPASS_MANAGER
+	select PCI_P2PDMA_CORE
+	select DMA_SHARED_BUFFER
 
 config VFIO_PCI_INTX
 	def_bool y if !S390
@@ -56,7 +58,8 @@ config VFIO_PCI_ZDEV_KVM
 	  To enable s390x KVM vfio-pci extensions, say Y.
 
 config VFIO_PCI_DMABUF
-	def_bool y if VFIO_PCI_CORE && PCI_P2PDMA && DMA_SHARED_BUFFER
+	def_bool y if PCI_P2PDMA
+	depends on VFIO_PCI_CORE
 
 source "drivers/vfio/pci/mlx5/Kconfig"
 
diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
index 6138f1bf241d..881452ea89be 100644
--- a/drivers/vfio/pci/Makefile
+++ b/drivers/vfio/pci/Makefile
@@ -1,8 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 
-vfio-pci-core-y := vfio_pci_core.o vfio_pci_intrs.o vfio_pci_rdwr.o vfio_pci_config.o
+vfio-pci-core-y := vfio_pci_core.o vfio_pci_intrs.o vfio_pci_rdwr.o vfio_pci_config.o vfio_pci_dmabuf.o
 vfio-pci-core-$(CONFIG_VFIO_PCI_ZDEV_KVM) += vfio_pci_zdev.o
-vfio-pci-core-$(CONFIG_VFIO_PCI_DMABUF) += vfio_pci_dmabuf.o
 obj-$(CONFIG_VFIO_PCI_CORE) += vfio-pci-core.o
 
 vfio-pci-y := vfio_pci.o
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 041243a84d81..f9636d8f9e2a 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -1683,18 +1683,6 @@ void vfio_pci_memory_unlock_and_restore(struct vfio_pci_core_device *vdev, u16 c
 	up_write(&vdev->memory_lock);
 }
 
-static unsigned long vma_to_pfn(struct vm_area_struct *vma)
-{
-	struct vfio_pci_core_device *vdev = vma->vm_private_data;
-	int index = vma->vm_pgoff >> (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT);
-	u64 pgoff;
-
-	pgoff = vma->vm_pgoff &
-		((1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) - 1);
-
-	return (pci_resource_start(vdev->pdev, index) >> PAGE_SHIFT) + pgoff;
-}
-
 vm_fault_t vfio_pci_vmf_insert_pfn(struct vfio_pci_core_device *vdev,
 				   struct vm_fault *vmf,
 				   unsigned long pfn,
@@ -1722,23 +1710,42 @@ static vm_fault_t vfio_pci_mmap_huge_fault(struct vm_fault *vmf,
 					   unsigned int order)
 {
 	struct vm_area_struct *vma = vmf->vma;
-	struct vfio_pci_core_device *vdev = vma->vm_private_data;
-	unsigned long addr = vmf->address & ~((PAGE_SIZE << order) - 1);
-	unsigned long pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
-	unsigned long pfn = vma_to_pfn(vma) + pgoff;
-	vm_fault_t ret = VM_FAULT_FALLBACK;
-
-	if (is_aligned_for_order(vma, addr, pfn, order)) {
-		scoped_guard(rwsem_read, &vdev->memory_lock)
-			ret = vfio_pci_vmf_insert_pfn(vdev, vmf, pfn, order);
+	struct vfio_pci_dma_buf *priv = vma->vm_private_data;
+	struct vfio_pci_core_device *vdev;
+	unsigned long pfn = 0;
+	vm_fault_t ret = VM_FAULT_SIGBUS;
+
+	/*
+	 * We can rely on the existence of both a DMABUF (priv) and
+	 * the VFIO device it was exported from (vdev).  This fault's
+	 * VMA was established using vfio_pci_core_mmap_prep_dmabuf()
+	 * which transfers ownership of the VFIO device fd to the
+	 * DMABUF, and so the VFIO device is held open because the
+	 * VMA's vm_file (DMABUF) is open.
+	 *
+	 * Since vfio_pci_dma_buf_cleanup() cannot have happened,
+	 * vdev must be valid; we can take memory_lock.
+	 */
+	vdev = priv->vdev;
+
+	scoped_guard(rwsem_read, &vdev->memory_lock) {
+		if (!priv->revoked) {
+			int pres = vfio_pci_dma_buf_find_pfn(priv, vma,
+							     vmf->address,
+							     order, &pfn);
+
+			if (pres == 0)
+				ret = vfio_pci_vmf_insert_pfn(vdev, vmf,
+							      pfn, order);
+			else if (pres == -EAGAIN)
+				ret = VM_FAULT_FALLBACK;
+		}
 	}
 
 	dev_dbg_ratelimited(&vdev->pdev->dev,
-			   "%s(,order = %d) BAR %ld page offset 0x%lx: 0x%x\n",
-			    __func__, order,
-			    vma->vm_pgoff >>
-				(VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT),
-			    pgoff, (unsigned int)ret);
+			    "%s(order = %d) PFN 0x%lx, VA 0x%lx, pgoff 0x%lx: 0x%x\n",
+			    __func__, order, pfn, vmf->address,
+			    vma->vm_pgoff, (unsigned int)ret);
 
 	return ret;
 }
@@ -1763,6 +1770,7 @@ int vfio_pci_core_mmap(struct vfio_device *core_vdev, struct vm_area_struct *vma
 	unsigned int index;
 	u64 phys_len, req_len, pgoff, req_start;
 	void __iomem *bar_io;
+	int ret;
 
 	index = vma->vm_pgoff >> (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT);
 
@@ -1802,7 +1810,20 @@ int vfio_pci_core_mmap(struct vfio_device *core_vdev, struct vm_area_struct *vma
 	if (IS_ERR(bar_io))
 		return PTR_ERR(bar_io);
 
-	vma->vm_private_data = vdev;
+	/*
+	 * Create a DMABUF with a single range corresponding to this
+	 * mapping, and wire it into vma->vm_private_data.  The VMA's
+	 * vm_file becomes that of the DMABUF, and the DMABUF takes
+	 * ownership of the VFIO device file (put upon DMABUF
+	 * release).  This maintains the behaviour of a live VMA
+	 * mapping holding the VFIO device file open.
+	 */
+	ret = vfio_pci_core_mmap_prep_dmabuf(vdev, vma,
+					     pci_resource_start(pdev, index),
+					     req_len, index);
+	if (ret)
+		return ret;
+
 	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 	vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
 
diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index 21180acf9600..2fd3629789bf 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -9,6 +9,7 @@
 
 MODULE_IMPORT_NS("DMA_BUF");
 
+#ifdef CONFIG_VFIO_PCI_DMABUF
 static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
 				   struct dma_buf_attachment *attachment)
 {
@@ -25,6 +26,7 @@ static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
 
 	return 0;
 }
+#endif /* CONFIG_VFIO_PCI_DMABUF */
 
 static void vfio_pci_dma_buf_done(struct kref *kref)
 {
@@ -89,7 +91,9 @@ static void vfio_pci_dma_buf_release(struct dma_buf *dmabuf)
 }
 
 static const struct dma_buf_ops vfio_pci_dmabuf_ops = {
+#ifdef CONFIG_VFIO_PCI_DMABUF
 	.attach = vfio_pci_dma_buf_attach,
+#endif
 	.map_dma_buf = vfio_pci_dma_buf_map,
 	.unmap_dma_buf = vfio_pci_dma_buf_unmap,
 	.release = vfio_pci_dma_buf_release,
@@ -258,6 +262,7 @@ static int vfio_pci_dmabuf_export(struct vfio_pci_core_device *vdev,
 	return 0;
 }
 
+#ifdef CONFIG_VFIO_PCI_DMABUF
 /*
  * This is a temporary "private interconnect" between VFIO DMABUF and iommufd.
  * It allows the two co-operating drivers to exchange the physical address of
@@ -456,6 +461,7 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 	kfree(dma_ranges);
 	return ret;
 }
+#endif /* CONFIG_VFIO_PCI_DMABUF */
 
 int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
 				   struct vm_area_struct *vma,
@@ -532,6 +538,10 @@ void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
 	struct vfio_pci_dma_buf *tmp;
 
 	lockdep_assert_held_write(&vdev->memory_lock);
+	/*
+	 * Holding memory_lock ensures a racing VMA fault observes
+	 * priv->revoked properly.
+	 */
 
 	list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm) {
 		if (!get_file_active(&priv->dmabuf->file))
@@ -549,6 +559,8 @@ void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
 			if (revoked) {
 				kref_put(&priv->kref, vfio_pci_dma_buf_done);
 				wait_for_completion(&priv->comp);
+				unmap_mapping_range(priv->dmabuf->file->f_mapping,
+						    0, priv->size, 1);
 				/*
 				 * Re-arm the registered kref reference and the
 				 * completion so the post-revoke state matches the
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index 06dc0fd3e230..d38e1b98b2e9 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -138,13 +138,13 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
 				   struct vm_area_struct *vma,
 				   u64 phys_start, u64 req_len,
 				   unsigned int res_index);
+void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev);
+void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked);
 
 #ifdef CONFIG_VFIO_PCI_DMABUF
 int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 				  struct vfio_device_feature_dma_buf __user *arg,
 				  size_t argsz);
-void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev);
-void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked);
 #else
 static inline int
 vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
@@ -153,13 +153,6 @@ vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 {
 	return -ENOTTY;
 }
-static inline void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev)
-{
-}
-static inline void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev,
-					 bool revoked)
-{
-}
 #endif
 
 #endif
-- 
2.50.1 (Apple Git-155)

[PATCH v3 5/9] vfio/pci: Provide a user-facing name for BAR mappings

[Matt Evans]

Since converting BAR mmap()s to using DMABUFs, we lose the original
device path in /proc/<pid>/maps, lsof, etc.  Generate a debug-oriented
synthetic 'filename' based on the cdev, plus BDF, plus resource index.

This applies only to BAR mappings via the VFIO device fd, as
explicitly-exported DMABUFs are named by userspace via the
DMA_BUF_SET_NAME ioctl.

Signed-off-by: Matt Evans <matt@ozlabs.org>
---
 drivers/vfio/pci/vfio_pci_dmabuf.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index 2fd3629789bf..8f7f1b909b94 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -4,6 +4,7 @@
 #include <linux/dma-buf-mapping.h>
 #include <linux/pci-p2pdma.h>
 #include <linux/dma-resv.h>
+#include <uapi/linux/dma-buf.h>
 
 #include "vfio_pci_priv.h"
 
@@ -470,6 +471,7 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
 {
 	struct vfio_pci_dma_buf *priv;
 	unsigned long vma_pgoff = vma->vm_pgoff & (VFIO_PCI_OFFSET_MASK >> PAGE_SHIFT);
+	char *bufname;
 	int ret;
 
 	priv = kzalloc_obj(*priv);
@@ -482,6 +484,20 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
 		goto err_free_priv;
 	}
 
+	bufname = kzalloc(DMA_BUF_NAME_LEN, GFP_KERNEL);
+	if (!bufname) {
+		ret = -ENOMEM;
+		goto err_free_phys;
+	}
+
+	/*
+	 * Maximum size of the friendly debug name is
+	 * vfio1234567890:ffff:ff:3f.7/5 = 30, which fits within
+	 * DMA_BUF_NAME_LEN.
+	 */
+	snprintf(bufname, DMA_BUF_NAME_LEN, "%s:%s/%x",
+		 dev_name(&vdev->vdev.device), pci_name(vdev->pdev), res_index);
+
 	/*
 	 * The DMABUF begins from the mmap()'s BAR offset, i.e. the
 	 * start of the VMA corresponds to byte 0 of the DMABUF and
@@ -500,7 +516,7 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
 	priv->provider = pcim_p2pdma_provider(vdev->pdev, res_index);
 	if (!priv->provider) {
 		ret = -EINVAL;
-		goto err_free_phys;
+		goto err_free_name;
 	}
 
 	priv->phys_vec[0].paddr = phys_start + ((u64)vma_pgoff << PAGE_SHIFT);
@@ -508,7 +524,7 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
 
 	ret = vfio_pci_dmabuf_export(vdev, priv, O_CLOEXEC | O_RDWR);
 	if (ret)
-		goto err_free_phys;
+		goto err_free_name;
 
 	/*
 	 * Ownership of the DMABUF file transfers to the VMA so that
@@ -523,8 +539,15 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
 	vma->vm_file = priv->dmabuf->file;
 	vma->vm_private_data = priv;
 
+	spin_lock(&priv->dmabuf->name_lock);
+	kfree(priv->dmabuf->name);
+	priv->dmabuf->name = bufname;
+	spin_unlock(&priv->dmabuf->name_lock);
+
 	return 0;
 
+err_free_name:
+	kfree(bufname);
 err_free_phys:
 	kfree(priv->phys_vec);
 err_free_priv:
-- 
2.50.1 (Apple Git-155)

[PATCH v3 6/9] vfio/pci: Clean up BAR zap and revocation

[Matt Evans]

Previously, vfio_pci_zap_bars() (and the wrapper
vfio_pci_zap_and_down_write_memory_lock()) calls were paired with
calls to vfio_pci_dma_buf_move().

This commit replaces them with a unified new function,
vfio_pci_zap_revoke_bars() containing both the vfio_pci_dma_buf_move()
and the unmap_mapping_range(), making it harder for callers to omit
one.  It adds a wrapper, vfio_pci_lock_zap_revoke_bars(), which takes
the write memory_lock before zapping, and adds a new
vfio_pci_unrevoke_bars() for the re-enable path.

As of "vfio/pci: Convert BAR mmap() to use a DMABUF", the
unmap_mapping_range() to zap is no longer performed for vfio-pci since
the DMABUFs used for BAR mappings already zap PTEs when the
vfio_pci_dma_buf_move() occurs.

However, it must be assumed that VFIO drivers which override the .mmap
op could create mappings _not_ backed by DMABUFs.  So, the zap is
still performed on revoke if .mmap is overridden, using a new
zap_bars_on_revoke flag.  A driver can explicitly opt out; the flag is
cleared by the hisi_acc_vfio_pci driver, since its .mmap just wraps
vfio_pci_core_mmap() and so still uses DMABUFs.

Signed-off-by: Matt Evans <matt@ozlabs.org>
---
 .../vfio/pci/hisilicon/hisi_acc_vfio_pci.c    |  8 +++
 drivers/vfio/pci/vfio_pci_config.c            | 30 ++++----
 drivers/vfio/pci/vfio_pci_core.c              | 70 +++++++++++++------
 drivers/vfio/pci/vfio_pci_priv.h              |  3 +-
 include/linux/vfio_pci_core.h                 |  1 +
 5 files changed, 73 insertions(+), 39 deletions(-)

diff --git a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
index 86362ec424a5..51990f6d66d5 100644
--- a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
+++ b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
@@ -1692,6 +1692,14 @@ static int hisi_acc_vfio_pci_probe(struct pci_dev *pdev, const struct pci_device
 	if (ret)
 		goto out_put_vdev;
 
+	/*
+	 * hisi_acc_vfio_pci_mmap() calls down to
+	 * vfio_pci_core_mmap(), so BAR mappings are still
+	 * DMABUF-backed.  They don't require a zap on revoke, so opt
+	 * out:
+	 */
+	hisi_acc_vdev->core_device.zap_bars_on_revoke = false;
+
 	hisi_acc_vfio_debug_init(hisi_acc_vdev);
 	return 0;
 
diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
index a10ed733f0e3..8bfab0da481c 100644
--- a/drivers/vfio/pci/vfio_pci_config.c
+++ b/drivers/vfio/pci/vfio_pci_config.c
@@ -590,12 +590,10 @@ static int vfio_basic_config_write(struct vfio_pci_core_device *vdev, int pos,
 		virt_mem = !!(le16_to_cpu(*virt_cmd) & PCI_COMMAND_MEMORY);
 		new_mem = !!(new_cmd & PCI_COMMAND_MEMORY);
 
-		if (!new_mem) {
-			vfio_pci_zap_and_down_write_memory_lock(vdev);
-			vfio_pci_dma_buf_move(vdev, true);
-		} else {
+		if (!new_mem)
+			vfio_pci_lock_zap_revoke_bars(vdev);
+		else
 			down_write(&vdev->memory_lock);
-		}
 
 		/*
 		 * If the user is writing mem/io enable (new_mem/io) and we
@@ -631,7 +629,7 @@ static int vfio_basic_config_write(struct vfio_pci_core_device *vdev, int pos,
 		*virt_cmd |= cpu_to_le16(new_cmd & mask);
 
 		if (__vfio_pci_memory_enabled(vdev))
-			vfio_pci_dma_buf_move(vdev, false);
+			vfio_pci_unrevoke_bars(vdev);
 		up_write(&vdev->memory_lock);
 	}
 
@@ -712,16 +710,14 @@ static int __init init_pci_cap_basic_perm(struct perm_bits *perm)
 static void vfio_lock_and_set_power_state(struct vfio_pci_core_device *vdev,
 					  pci_power_t state)
 {
-	if (state >= PCI_D3hot) {
-		vfio_pci_zap_and_down_write_memory_lock(vdev);
-		vfio_pci_dma_buf_move(vdev, true);
-	} else {
+	if (state >= PCI_D3hot)
+		vfio_pci_lock_zap_revoke_bars(vdev);
+	else
 		down_write(&vdev->memory_lock);
-	}
 
 	vfio_pci_set_power_state(vdev, state);
 	if (__vfio_pci_memory_enabled(vdev))
-		vfio_pci_dma_buf_move(vdev, false);
+		vfio_pci_unrevoke_bars(vdev);
 	up_write(&vdev->memory_lock);
 }
 
@@ -908,11 +904,10 @@ static int vfio_exp_config_write(struct vfio_pci_core_device *vdev, int pos,
 						 &cap);
 
 		if (!ret && (cap & PCI_EXP_DEVCAP_FLR)) {
-			vfio_pci_zap_and_down_write_memory_lock(vdev);
-			vfio_pci_dma_buf_move(vdev, true);
+			vfio_pci_lock_zap_revoke_bars(vdev);
 			pci_try_reset_function(vdev->pdev);
 			if (__vfio_pci_memory_enabled(vdev))
-				vfio_pci_dma_buf_move(vdev, false);
+				vfio_pci_unrevoke_bars(vdev);
 			up_write(&vdev->memory_lock);
 		}
 	}
@@ -993,11 +988,10 @@ static int vfio_af_config_write(struct vfio_pci_core_device *vdev, int pos,
 						&cap);
 
 		if (!ret && (cap & PCI_AF_CAP_FLR) && (cap & PCI_AF_CAP_TP)) {
-			vfio_pci_zap_and_down_write_memory_lock(vdev);
-			vfio_pci_dma_buf_move(vdev, true);
+			vfio_pci_lock_zap_revoke_bars(vdev);
 			pci_try_reset_function(vdev->pdev);
 			if (__vfio_pci_memory_enabled(vdev))
-				vfio_pci_dma_buf_move(vdev, false);
+				vfio_pci_unrevoke_bars(vdev);
 			up_write(&vdev->memory_lock);
 		}
 	}
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index f9636d8f9e2a..5ea0bd4e7876 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -319,8 +319,7 @@ static int vfio_pci_runtime_pm_entry(struct vfio_pci_core_device *vdev,
 	 * The vdev power related flags are protected with 'memory_lock'
 	 * semaphore.
 	 */
-	vfio_pci_zap_and_down_write_memory_lock(vdev);
-	vfio_pci_dma_buf_move(vdev, true);
+	vfio_pci_lock_zap_revoke_bars(vdev);
 
 	if (vdev->pm_runtime_engaged) {
 		up_write(&vdev->memory_lock);
@@ -406,7 +405,7 @@ static void vfio_pci_runtime_pm_exit(struct vfio_pci_core_device *vdev)
 	down_write(&vdev->memory_lock);
 	__vfio_pci_runtime_pm_exit(vdev);
 	if (__vfio_pci_memory_enabled(vdev))
-		vfio_pci_dma_buf_move(vdev, false);
+		vfio_pci_unrevoke_bars(vdev);
 	up_write(&vdev->memory_lock);
 }
 
@@ -1256,6 +1255,8 @@ static int vfio_pci_ioctl_set_irqs(struct vfio_pci_core_device *vdev,
 	return ret;
 }
 
+static void vfio_pci_zap_revoke_bars(struct vfio_pci_core_device *vdev);
+
 static int vfio_pci_ioctl_reset(struct vfio_pci_core_device *vdev,
 				void __user *arg)
 {
@@ -1264,7 +1265,7 @@ static int vfio_pci_ioctl_reset(struct vfio_pci_core_device *vdev,
 	if (!vdev->reset_works)
 		return -EINVAL;
 
-	vfio_pci_zap_and_down_write_memory_lock(vdev);
+	down_write(&vdev->memory_lock);
 
 	/*
 	 * This function can be invoked while the power state is non-D0. If
@@ -1277,10 +1278,11 @@ static int vfio_pci_ioctl_reset(struct vfio_pci_core_device *vdev,
 	 */
 	vfio_pci_set_power_state(vdev, PCI_D0);
 
-	vfio_pci_dma_buf_move(vdev, true);
+	vfio_pci_zap_revoke_bars(vdev);
+
 	ret = pci_try_reset_function(vdev->pdev);
 	if (__vfio_pci_memory_enabled(vdev))
-		vfio_pci_dma_buf_move(vdev, false);
+		vfio_pci_unrevoke_bars(vdev);
 	up_write(&vdev->memory_lock);
 
 	return ret;
@@ -1648,20 +1650,37 @@ ssize_t vfio_pci_core_write(struct vfio_device *core_vdev, const char __user *bu
 }
 EXPORT_SYMBOL_GPL(vfio_pci_core_write);
 
-static void vfio_pci_zap_bars(struct vfio_pci_core_device *vdev)
+static void vfio_pci_zap_revoke_bars(struct vfio_pci_core_device *vdev)
 {
-	struct vfio_device *core_vdev = &vdev->vdev;
-	loff_t start = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_BAR0_REGION_INDEX);
-	loff_t end = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_ROM_REGION_INDEX);
-	loff_t len = end - start;
+	lockdep_assert_held_write(&vdev->memory_lock);
+	vfio_pci_dma_buf_move(vdev, true);
 
-	unmap_mapping_range(core_vdev->inode->i_mapping, start, len, true);
+	/*
+	 * If a driver could possibly create BAR mappings in the
+	 * vdev's address_space, do an additional zap on revoke.  See
+	 * vfio_pci_core_register_device().
+	 */
+	if (vdev->zap_bars_on_revoke) {
+		struct vfio_device *core_vdev = &vdev->vdev;
+		loff_t start = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_BAR0_REGION_INDEX);
+		loff_t end = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_ROM_REGION_INDEX);
+		loff_t len = end - start;
+
+		unmap_mapping_range(core_vdev->inode->i_mapping,
+				    start, len, true);
+	}
 }
 
-void vfio_pci_zap_and_down_write_memory_lock(struct vfio_pci_core_device *vdev)
+void vfio_pci_lock_zap_revoke_bars(struct vfio_pci_core_device *vdev)
 {
 	down_write(&vdev->memory_lock);
-	vfio_pci_zap_bars(vdev);
+	vfio_pci_zap_revoke_bars(vdev);
+}
+
+void vfio_pci_unrevoke_bars(struct vfio_pci_core_device *vdev)
+{
+	lockdep_assert_held_write(&vdev->memory_lock);
+	vfio_pci_dma_buf_move(vdev, false);
 }
 
 u16 vfio_pci_memory_lock_and_enable(struct vfio_pci_core_device *vdev)
@@ -2242,6 +2261,17 @@ int vfio_pci_core_register_device(struct vfio_pci_core_device *vdev)
 	if (ret)
 		goto out_vf;
 
+	/*
+	 * If a driver overrides .mmap, it has to be assumed that it
+	 * might not use the DMABUF-backed core mmap; this flag
+	 * enables a zap at revoke time.  Drivers can opt out by
+	 * clearing this flag after registration, e.g. if their .mmap
+	 * override calls down to vfio_pci_core_mmap() so that maps
+	 * are DMABUF-backed.
+	 */
+	if (vdev->vdev.ops->mmap != vfio_pci_core_mmap)
+		vdev->zap_bars_on_revoke = true;
+
 	vfio_pci_probe_power_state(vdev);
 
 	/*
@@ -2517,9 +2547,10 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
 		}
 
 		/*
-		 * Take the memory write lock for each device and zap BAR
-		 * mappings to prevent the user accessing the device while in
-		 * reset.  Locking multiple devices is prone to deadlock,
+		 * Take the memory write lock for each device and
+		 * zap/revoke BAR mappings to prevent the user (or
+		 * peers) accessing the device while in reset.
+		 * Locking multiple devices is prone to deadlock,
 		 * runaway and unwind if we hit contention.
 		 */
 		if (!down_write_trylock(&vdev->memory_lock)) {
@@ -2527,8 +2558,7 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
 			break;
 		}
 
-		vfio_pci_dma_buf_move(vdev, true);
-		vfio_pci_zap_bars(vdev);
+		vfio_pci_zap_revoke_bars(vdev);
 	}
 
 	if (!list_entry_is_head(vdev,
@@ -2558,7 +2588,7 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
 	list_for_each_entry_from_reverse(vdev, &dev_set->device_list,
 					 vdev.dev_set_list) {
 		if (vdev->vdev.open_count && __vfio_pci_memory_enabled(vdev))
-			vfio_pci_dma_buf_move(vdev, false);
+			vfio_pci_unrevoke_bars(vdev);
 		up_write(&vdev->memory_lock);
 	}
 
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index d38e1b98b2e9..10833aabd7fb 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -83,7 +83,8 @@ void vfio_config_free(struct vfio_pci_core_device *vdev);
 int vfio_pci_set_power_state(struct vfio_pci_core_device *vdev,
 			     pci_power_t state);
 
-void vfio_pci_zap_and_down_write_memory_lock(struct vfio_pci_core_device *vdev);
+void vfio_pci_lock_zap_revoke_bars(struct vfio_pci_core_device *vdev);
+void vfio_pci_unrevoke_bars(struct vfio_pci_core_device *vdev);
 u16 vfio_pci_memory_lock_and_enable(struct vfio_pci_core_device *vdev);
 void vfio_pci_memory_unlock_and_restore(struct vfio_pci_core_device *vdev,
 					u16 cmd);
diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
index 7accd0eac457..93629b7fb8b8 100644
--- a/include/linux/vfio_pci_core.h
+++ b/include/linux/vfio_pci_core.h
@@ -127,6 +127,7 @@ struct vfio_pci_core_device {
 	bool			needs_pm_restore:1;
 	bool			pm_intx_masked:1;
 	bool			pm_runtime_engaged:1;
+	bool			zap_bars_on_revoke:1;
 	struct pci_saved_state	*pci_saved_state;
 	struct pci_saved_state	*pm_save;
 	int			ioeventfds_nr;
-- 
2.50.1 (Apple Git-155)

[PATCH v3 7/9] vfio/pci: Support mmap() of a VFIO DMABUF

[Matt Evans]

A VFIO DMABUF can export a subset of a BAR to userspace by fd; add
support for mmap() of this fd.  This provides another route for a
process to map BARs, in which the process can only map a specific
subset of a BAR represented by the exported DMABUF.

mmap() support enables userspace driver designs that safely delegate
access to BAR sub-ranges to other client processes by sharing a DMABUF
fd, without having to share the (omnipotent) VFIO device fd with them.

Since the main VFIO BAR mmap() is now DMABUF-aware, the new mmap() reuses
the existing vm_ops.

The lifecycle of an exported DMABUF remains decoupled from that of the
device fd it came from, i.e. the device fd could be closed with DMABUF
VMAs present, meaning a fault on a VMA could happen concurrently with
vfio_pci_dma_buf_cleanup().

To deal with this scenario, the fault handler now temporarily takes a
VFIO device registration to ensure the vdev remains valid, and then
vdev->memory_lock can be taken on it.

Signed-off-by: Matt Evans <matt@ozlabs.org>
---
 drivers/vfio/pci/vfio_pci_core.c   | 80 ++++++++++++++++++++++++++----
 drivers/vfio/pci/vfio_pci_dmabuf.c | 36 ++++++++++++++
 drivers/vfio/pci/vfio_pci_priv.h   |  2 +
 3 files changed, 109 insertions(+), 9 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 5ea0bd4e7876..508a5eca910a 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -12,6 +12,8 @@
 
 #include <linux/aperture.h>
 #include <linux/device.h>
+#include <linux/dma-buf.h>
+#include <linux/dma-resv.h>
 #include <linux/eventfd.h>
 #include <linux/file.h>
 #include <linux/interrupt.h>
@@ -1735,19 +1737,78 @@ static vm_fault_t vfio_pci_mmap_huge_fault(struct vm_fault *vmf,
 	vm_fault_t ret = VM_FAULT_SIGBUS;
 
 	/*
-	 * We can rely on the existence of both a DMABUF (priv) and
-	 * the VFIO device it was exported from (vdev).  This fault's
-	 * VMA was established using vfio_pci_core_mmap_prep_dmabuf()
-	 * which transfers ownership of the VFIO device fd to the
-	 * DMABUF, and so the VFIO device is held open because the
-	 * VMA's vm_file (DMABUF) is open.
+	 * The only thing this can rely on is that the DMABUF relating
+	 * to the VMA's vm_file exists (priv).
 	 *
-	 * Since vfio_pci_dma_buf_cleanup() cannot have happened,
-	 * vdev must be valid; we can take memory_lock.
+	 * A DMABUF for a VFIO device fd mmap() holds a reference to
+	 * the original VFIO device fd, but an explicitly-exported
+	 * DMABUF does not.  The original fd might have closed,
+	 * meaning this fault can race with
+	 * vfio_pci_dma_buf_cleanup(), meaning the buffer could have
+	 * been revoked (in which case priv->vdev might be NULL), and
+	 * the VFIO device registration might have been dropped.
+	 *
+	 * With the goal of taking vdev->memory_lock in a world where
+	 * vdev might not still exist:
+	 *
+	 * 1. Take the resv lock on the DMABUF:
+	 *  - If racing cleanup got in first, the buffer is revoked;
+	 *    stop/exit if so.
+	 *  - If we got in first, the buffer is not revoked so vdev is
+	 *    non-NULL, accessible, and cleanup _has not yet put the
+	 *    VFIO device registration_.  So, the device refcount must
+	 *    be >0.
+	 *
+	 * 2. Take vfio_device registration (refcount guaranteed >0
+	 *    hereafter).
+	 *
+	 * 3. Unlock the DMABUF's resv lock:
+	 *  - A racing cleanup can now complete.
+	 *  - But, the device refcount >0, meaning the vfio_device
+	 *    (and vfio_pcie_core device vdev) have not yet been
+	 *    freed.  vdev is accessible, even if the DMABUF has been
+	 *    revoked or cleanup has happened, because
+	 *    vfio_unregister_group_dev() can't complete.
+	 *
+	 * 4. Take the vdev->memory_lock
+	 *  - Either the DMABUF is usable, or has been cleaned up.
+	 *    Whichever, it can no longer change under us.
+	 *  - Test the DMABUF revocation status again: if it was
+	 *    revoked between 1 and 4 return a SIGBUS. Otherwise,
+	 *    return a PFN.
+	 *  - It's not necessary to also take the resv lock, because
+	 *    the status/vdev can't change while memory_lock is held.
+	 *
+	 * 5. Unlock, done.
 	 */
+
+	dma_resv_lock(priv->dmabuf->resv, NULL);
+
+	if (priv->revoked) {
+		pr_debug_ratelimited("%s VA 0x%lx, pgoff 0x%lx: DMABUF revoked/cleaned up\n",
+				     __func__, vmf->address, vma->vm_pgoff);
+		dma_resv_unlock(priv->dmabuf->resv);
+		return VM_FAULT_SIGBUS;
+	}
+
+	/* If the buffer isn't revoked, vdev is valid */
 	vdev = priv->vdev;
 
+	if (!vfio_device_try_get_registration(&vdev->vdev)) {
+		/*
+		 * If vdev != NULL (above), the registration should
+		 * already be >0 and so this try_get should never
+		 * fail.
+		 */
+		dev_warn(&vdev->pdev->dev, "%s: Unexpected registration failure\n",
+			 __func__);
+		dma_resv_unlock(priv->dmabuf->resv);
+		return VM_FAULT_SIGBUS;
+	}
+	dma_resv_unlock(priv->dmabuf->resv);
+
 	scoped_guard(rwsem_read, &vdev->memory_lock) {
+		/* Revocation status must be re-read, under memory_lock */
 		if (!priv->revoked) {
 			int pres = vfio_pci_dma_buf_find_pfn(priv, vma,
 							     vmf->address,
@@ -1766,6 +1827,7 @@ static vm_fault_t vfio_pci_mmap_huge_fault(struct vm_fault *vmf,
 			    __func__, order, pfn, vmf->address,
 			    vma->vm_pgoff, (unsigned int)ret);
 
+	vfio_device_put_registration(&vdev->vdev);
 	return ret;
 }
 
@@ -1774,7 +1836,7 @@ static vm_fault_t vfio_pci_mmap_page_fault(struct vm_fault *vmf)
 	return vfio_pci_mmap_huge_fault(vmf, 0);
 }
 
-static const struct vm_operations_struct vfio_pci_mmap_ops = {
+const struct vm_operations_struct vfio_pci_mmap_ops = {
 	.fault = vfio_pci_mmap_page_fault,
 #ifdef CONFIG_ARCH_SUPPORTS_HUGE_PFNMAP
 	.huge_fault = vfio_pci_mmap_huge_fault,
diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index 8f7f1b909b94..2fb09a2c0f6b 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -27,6 +27,41 @@ static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
 
 	return 0;
 }
+
+static int vfio_pci_dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
+{
+	struct vfio_pci_dma_buf *priv = dmabuf->priv;
+
+	/*
+	 * If we observe that the buffer is revoked now then refuse
+	 * the mmap().  This is a belt-and-braces early failure to
+	 * ease debugging a revoked buffer being used.  Userspace
+	 * might also race an mmap() against an explicit revocation,
+	 * or an action doing a temporary revoke; race scenarios are
+	 * still safe because the fault handler ultimately prevents
+	 * access to a revoked buffer if it isn't caught here.
+	 */
+	if (READ_ONCE(priv->revoked))
+		return -ENODEV;
+	if ((vma->vm_flags & VM_SHARED) == 0)
+		return -EINVAL;
+
+	/*
+	 * dma_buf_mmap_internal() has asserted that the VMA is
+	 * contained within the DMABUF size before calling this.
+	 */
+
+	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+	vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
+
+	/* See comments in vfio_pci_core_mmap() re VM_ALLOW_ANY_UNCACHED. */
+	vm_flags_set(vma, VM_ALLOW_ANY_UNCACHED | VM_IO | VM_PFNMAP |
+		     VM_DONTEXPAND | VM_DONTDUMP);
+	vma->vm_private_data = priv;
+	vma->vm_ops = &vfio_pci_mmap_ops;
+
+	return 0;
+}
 #endif /* CONFIG_VFIO_PCI_DMABUF */
 
 static void vfio_pci_dma_buf_done(struct kref *kref)
@@ -94,6 +129,7 @@ static void vfio_pci_dma_buf_release(struct dma_buf *dmabuf)
 static const struct dma_buf_ops vfio_pci_dmabuf_ops = {
 #ifdef CONFIG_VFIO_PCI_DMABUF
 	.attach = vfio_pci_dma_buf_attach,
+	.mmap = vfio_pci_dma_buf_mmap,
 #endif
 	.map_dma_buf = vfio_pci_dma_buf_map,
 	.unmap_dma_buf = vfio_pci_dma_buf_unmap,
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index 10833aabd7fb..db2e2aeae88f 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -38,6 +38,8 @@ struct vfio_pci_dma_buf {
 	u8 revoked : 1;
 };
 
+extern const struct vm_operations_struct vfio_pci_mmap_ops;
+
 bool vfio_pci_intx_mask(struct vfio_pci_core_device *vdev);
 void vfio_pci_intx_unmask(struct vfio_pci_core_device *vdev);
 
-- 
2.50.1 (Apple Git-155)

[PATCH v3 8/9] vfio/pci: Permanently revoke a DMABUF on request

[Matt Evans]

Expand the VFIO DMABUF revocation state to three states:
Not revoked, temporarily revoked, and permanently revoked.

The first two are for existing transient revocation, e.g. across a
function reset, and the DMABUF is put into the last in response to a
new VFIO feature VFIO_DEVICE_FEATURE_DMA_BUF.

VFIO_DEVICE_FEATURE_DMA_BUF passes a DMABUF by fd and requests that
the DMABUF is permanently revoked.  On success, it's guaranteed that
the buffer can never be imported/attached/mmap()ed in future, that
dynamic imports have been cleanly detached, and that all mappings have
been made inaccessible/PTEs zapped.

This is useful for lifecycle management, to reclaim VFIO PCI BAR
ranges previously delegated to a subordinate client process: The
driver process can ensure that the loaned resources are revoked when
the client is deemed "done", and exported ranges can be safely re-used
elsewhere.

Refactor the revocation code out of vfio_pci_dma_buf_move() to a
function common to move and the new feature request path.

Signed-off-by: Matt Evans <matt@ozlabs.org>
---
 drivers/vfio/pci/vfio_pci_core.c   |   6 +-
 drivers/vfio/pci/vfio_pci_dmabuf.c | 169 ++++++++++++++++++++++-------
 drivers/vfio/pci/vfio_pci_priv.h   |  19 +++-
 include/uapi/linux/vfio.h          |  20 ++++
 4 files changed, 173 insertions(+), 41 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 508a5eca910a..064906b25467 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -1573,6 +1573,8 @@ int vfio_pci_core_ioctl_feature(struct vfio_device *device, u32 flags,
 		return vfio_pci_core_feature_token(vdev, flags, arg, argsz);
 	case VFIO_DEVICE_FEATURE_DMA_BUF:
 		return vfio_pci_core_feature_dma_buf(vdev, flags, arg, argsz);
+	case VFIO_DEVICE_FEATURE_DMA_BUF_REVOKE:
+		return vfio_pci_core_feature_dma_buf_revoke(vdev, flags, arg, argsz);
 	default:
 		return -ENOTTY;
 	}
@@ -1784,7 +1786,7 @@ static vm_fault_t vfio_pci_mmap_huge_fault(struct vm_fault *vmf,
 
 	dma_resv_lock(priv->dmabuf->resv, NULL);
 
-	if (priv->revoked) {
+	if (priv->status != VFIO_PCI_DMABUF_OK) {
 		pr_debug_ratelimited("%s VA 0x%lx, pgoff 0x%lx: DMABUF revoked/cleaned up\n",
 				     __func__, vmf->address, vma->vm_pgoff);
 		dma_resv_unlock(priv->dmabuf->resv);
@@ -1809,7 +1811,7 @@ static vm_fault_t vfio_pci_mmap_huge_fault(struct vm_fault *vmf,
 
 	scoped_guard(rwsem_read, &vdev->memory_lock) {
 		/* Revocation status must be re-read, under memory_lock */
-		if (!priv->revoked) {
+		if (priv->status == VFIO_PCI_DMABUF_OK) {
 			int pres = vfio_pci_dma_buf_find_pfn(priv, vma,
 							     vmf->address,
 							     order, &pfn);
diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index 2fb09a2c0f6b..b47411992ab6 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -19,7 +19,7 @@ static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
 	if (!attachment->peer2peer)
 		return -EOPNOTSUPP;
 
-	if (priv->revoked)
+	if (priv->status != VFIO_PCI_DMABUF_OK)
 		return -ENODEV;
 
 	if (!dma_buf_attach_revocable(attachment))
@@ -41,7 +41,7 @@ static int vfio_pci_dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *
 	 * still safe because the fault handler ultimately prevents
 	 * access to a revoked buffer if it isn't caught here.
 	 */
-	if (READ_ONCE(priv->revoked))
+	if (READ_ONCE(priv->status) != VFIO_PCI_DMABUF_OK)
 		return -ENODEV;
 	if ((vma->vm_flags & VM_SHARED) == 0)
 		return -EINVAL;
@@ -81,7 +81,7 @@ vfio_pci_dma_buf_map(struct dma_buf_attachment *attachment,
 
 	dma_resv_assert_held(priv->dmabuf->resv);
 
-	if (priv->revoked)
+	if (priv->status != VFIO_PCI_DMABUF_OK)
 		return ERR_PTR(-ENODEV);
 
 	ret = dma_buf_phys_vec_to_sgt(attachment, priv->provider,
@@ -291,7 +291,8 @@ static int vfio_pci_dmabuf_export(struct vfio_pci_core_device *vdev,
 	INIT_LIST_HEAD(&priv->dmabufs_elm);
 	down_write(&vdev->memory_lock);
 	dma_resv_lock(priv->dmabuf->resv, NULL);
-	priv->revoked = !__vfio_pci_memory_enabled(vdev);
+	priv->status = __vfio_pci_memory_enabled(vdev) ? VFIO_PCI_DMABUF_OK :
+		VFIO_PCI_DMABUF_TEMP_REVOKED;
 	list_add_tail(&priv->dmabufs_elm, &vdev->dmabufs);
 	dma_resv_unlock(priv->dmabuf->resv);
 	up_write(&vdev->memory_lock);
@@ -322,7 +323,7 @@ int vfio_pci_dma_buf_iommufd_map(struct dma_buf_attachment *attachment,
 		return -EOPNOTSUPP;
 
 	priv = attachment->dmabuf->priv;
-	if (priv->revoked)
+	if (priv->status != VFIO_PCI_DMABUF_OK)
 		return -ENODEV;
 
 	/* More than one range to iommufd will require proper DMABUF support */
@@ -591,6 +592,64 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
 	return ret;
 }
 
+/* Set the DMABUF's revocation status (OK or temporarily/permanently revoked) */
+static void vfio_pci_dma_buf_set_status(struct vfio_pci_dma_buf *priv,
+					enum vfio_pci_dma_buf_status new_status)
+{
+	bool was_revoked;
+
+	lockdep_assert_held_write(&priv->vdev->memory_lock);
+
+	if (priv->status == VFIO_PCI_DMABUF_PERM_REVOKED ||
+	    priv->status == new_status) {
+		return;
+	}
+
+	dma_resv_lock(priv->dmabuf->resv, NULL);
+	was_revoked = (priv->status == VFIO_PCI_DMABUF_TEMP_REVOKED);
+
+	if (new_status != VFIO_PCI_DMABUF_OK) {
+		priv->status = new_status; /* Temp or permanently revoked */
+
+		if (was_revoked) {
+			/*
+			 * TEMP_REVOKED is being upgraded to
+			 * PERM_REVOKED.  The buffer is already gone,
+			 * don't wait on it again.
+			 */
+			dma_resv_unlock(priv->dmabuf->resv);
+			return;
+		}
+	}
+
+	dma_buf_invalidate_mappings(priv->dmabuf);
+	dma_resv_wait_timeout(priv->dmabuf->resv,
+			      DMA_RESV_USAGE_BOOKKEEP, false,
+			      MAX_SCHEDULE_TIMEOUT);
+	dma_resv_unlock(priv->dmabuf->resv);
+	if (new_status != VFIO_PCI_DMABUF_OK) {
+		kref_put(&priv->kref, vfio_pci_dma_buf_done);
+		wait_for_completion(&priv->comp);
+		unmap_mapping_range(priv->dmabuf->file->f_mapping,
+				    0, priv->size, 1);
+		/*
+		 * Re-arm the registered kref reference and the
+		 * completion so the post-revoke state matches the
+		 * post-creation state.	 An un-revoke followed by a
+		 * new mapping needs the kref to be non-zero before
+		 * kref_get(), and vfio_pci_dma_buf_cleanup()
+		 * delegates its drain back through this revoke
+		 * path on a possibly-already-revoked dma-buf.
+		 */
+		kref_init(&priv->kref);
+		reinit_completion(&priv->comp);
+	} else {
+		dma_resv_lock(priv->dmabuf->resv, NULL);
+		priv->status = VFIO_PCI_DMABUF_OK;
+		dma_resv_unlock(priv->dmabuf->resv);
+	}
+}
+
 void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
 {
 	struct vfio_pci_dma_buf *priv;
@@ -599,44 +658,15 @@ void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
 	lockdep_assert_held_write(&vdev->memory_lock);
 	/*
 	 * Holding memory_lock ensures a racing VMA fault observes
-	 * priv->revoked properly.
+	 * priv->status properly.
 	 */
 
 	list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm) {
 		if (!get_file_active(&priv->dmabuf->file))
 			continue;
-
-		if (priv->revoked != revoked) {
-			dma_resv_lock(priv->dmabuf->resv, NULL);
-			if (revoked)
-				priv->revoked = true;
-			dma_buf_invalidate_mappings(priv->dmabuf);
-			dma_resv_wait_timeout(priv->dmabuf->resv,
-					      DMA_RESV_USAGE_BOOKKEEP, false,
-					      MAX_SCHEDULE_TIMEOUT);
-			dma_resv_unlock(priv->dmabuf->resv);
-			if (revoked) {
-				kref_put(&priv->kref, vfio_pci_dma_buf_done);
-				wait_for_completion(&priv->comp);
-				unmap_mapping_range(priv->dmabuf->file->f_mapping,
-						    0, priv->size, 1);
-				/*
-				 * Re-arm the registered kref reference and the
-				 * completion so the post-revoke state matches the
-				 * post-creation state.  An un-revoke followed by a
-				 * new mapping needs the kref to be non-zero before
-				 * kref_get(), and vfio_pci_dma_buf_cleanup()
-				 * delegates its drain back through this revoke
-				 * path on a possibly-already-revoked dma-buf.
-				 */
-				kref_init(&priv->kref);
-				reinit_completion(&priv->comp);
-			} else {
-				dma_resv_lock(priv->dmabuf->resv, NULL);
-				priv->revoked = false;
-				dma_resv_unlock(priv->dmabuf->resv);
-			}
-		}
+		vfio_pci_dma_buf_set_status(priv, revoked ?
+					    VFIO_PCI_DMABUF_TEMP_REVOKED :
+					    VFIO_PCI_DMABUF_OK);
 		fput(priv->dmabuf->file);
 	}
 }
@@ -668,3 +698,66 @@ void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev)
 	}
 	up_write(&vdev->memory_lock);
 }
+
+#ifdef CONFIG_VFIO_PCI_DMABUF
+int vfio_pci_core_feature_dma_buf_revoke(
+	struct vfio_pci_core_device *vdev, u32 flags,
+	struct vfio_device_feature_dma_buf_revoke __user *arg,
+	size_t argsz)
+{
+	struct vfio_device_feature_dma_buf_revoke db_revoke;
+	struct vfio_pci_dma_buf *priv;
+	struct dma_buf *dmabuf;
+	int ret;
+
+	if (!vdev->pci_ops || !vdev->pci_ops->get_dmabuf_phys)
+		return -EOPNOTSUPP;
+
+	ret = vfio_check_feature(flags, argsz,
+				 VFIO_DEVICE_FEATURE_SET,
+				 sizeof(db_revoke));
+	if (ret != 1)
+		return ret;
+
+	if (copy_from_user(&db_revoke, arg, sizeof(db_revoke)))
+		return -EFAULT;
+
+	dmabuf = dma_buf_get(db_revoke.dmabuf_fd);
+	if (IS_ERR(dmabuf))
+		return PTR_ERR(dmabuf);
+
+	priv = dmabuf->priv;
+	/*
+	 * Sanity-check the DMABUF is really a vfio_pci_dma_buf _and_
+	 * relates to the VFIO device it was provided with.
+	 *
+	 * If the DMABUF relates to this vdev then priv->vdev is
+	 * stable because this open fd prevents cleanup.
+	 *
+	 * If it relates to a different vdev, reading priv->vdev might
+	 * race with a concurrent cleanup on that device.  But if so,
+	 * it points to a non-matching vdev or NULL and is unusable
+	 * either way.
+	 */
+	if (dmabuf->ops != &vfio_pci_dmabuf_ops ||
+	    READ_ONCE(priv->vdev) != vdev) {
+		ret = -ENODEV;
+		goto out_put_buf;
+	}
+
+	scoped_guard(rwsem_write, &vdev->memory_lock) {
+		if (priv->status == VFIO_PCI_DMABUF_PERM_REVOKED) {
+			ret = -EBADFD;
+		} else {
+			vfio_pci_dma_buf_set_status(priv,
+						    VFIO_PCI_DMABUF_PERM_REVOKED);
+			ret = 0;
+		}
+	}
+
+out_put_buf:
+	dma_buf_put(dmabuf);
+
+	return ret;
+}
+#endif /* CONFIG_VFIO_PCI_DMABUF */
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index db2e2aeae88f..3c2f2575b670 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -23,6 +23,12 @@ struct vfio_pci_ioeventfd {
 	bool			test_mem;
 };
 
+enum vfio_pci_dma_buf_status {
+	VFIO_PCI_DMABUF_OK = 0,
+	VFIO_PCI_DMABUF_TEMP_REVOKED = 1,
+	VFIO_PCI_DMABUF_PERM_REVOKED = 2,
+};
+
 struct vfio_pci_dma_buf {
 	struct dma_buf *dmabuf;
 	struct vfio_pci_core_device *vdev;
@@ -35,7 +41,7 @@ struct vfio_pci_dma_buf {
 	struct kref kref;
 	struct completion comp;
 	unsigned long vma_pgoff_adjust;
-	u8 revoked : 1;
+	enum vfio_pci_dma_buf_status status;
 };
 
 extern const struct vm_operations_struct vfio_pci_mmap_ops;
@@ -148,6 +154,10 @@ void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked);
 int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 				  struct vfio_device_feature_dma_buf __user *arg,
 				  size_t argsz);
+int vfio_pci_core_feature_dma_buf_revoke(
+	struct vfio_pci_core_device *vdev, u32 flags,
+	struct vfio_device_feature_dma_buf_revoke __user *arg,
+	size_t argsz);
 #else
 static inline int
 vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
@@ -156,6 +166,13 @@ vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 {
 	return -ENOTTY;
 }
+static inline int vfio_pci_core_feature_dma_buf_revoke(
+	struct vfio_pci_core_device *vdev, u32 flags,
+	struct vfio_device_feature_dma_buf_revoke __user *arg,
+	size_t argsz)
+{
+	return -ENOTTY;
+}
 #endif
 
 #endif
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 5de618a3a5ee..697c0bb4b9bc 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -1534,6 +1534,26 @@ struct vfio_device_feature_dma_buf {
  */
 #define VFIO_DEVICE_FEATURE_MIG_PRECOPY_INFOv2  12
 
+/**
+ * Given a dma_buf fd previously created by
+ * VFIO_DEVICE_FEATURE_DMA_BUF, a SET of this feature requests that
+ * access to the corresponding DMABUF is immediately and permanently
+ * revoked.  On successful return, the buffer is not accessible
+ * through any mmap() or dma-buf import.  The buffer is permanently
+ * disabled, and VFIO refuses all map, mmap, attach, etc. requests.
+ *
+ * Return: 0 on success, -1 and errno is set on failure:
+ *
+ *  EBADF, EINVAL: dmabuf_fd is not a DMABUF fd.
+ *  ENODEV: The dmabuf_fd does not match this VFIO device.
+ *  EBADFD: The DMABUF is already revoked.
+ */
+#define VFIO_DEVICE_FEATURE_DMA_BUF_REVOKE 13
+
+struct vfio_device_feature_dma_buf_revoke {
+	__s32	dmabuf_fd;
+};
+
 /* -------- API for Type1 VFIO IOMMU -------- */
 
 /**
-- 
2.50.1 (Apple Git-155)

[PATCH v3 9/9] vfio/pci: Add mmap() attributes to DMABUF feature

[Matt Evans]

A new VFIO feature, VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR, is added to
set CPU-facing memory type attributes for a DMABUF exported from
vfio-pci.  These are used for subsequent mmap()s of the buffer.

There are two attributes supported:
 - The default, VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_NC
 - VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_WC, which results in WC
   PTEs for the DMABUF's BAR region.

Signed-off-by: Matt Evans <matt@ozlabs.org>
---
 drivers/vfio/pci/vfio_pci_core.c   |  2 ++
 drivers/vfio/pci/vfio_pci_dmabuf.c | 57 +++++++++++++++++++++++++++++-
 drivers/vfio/pci/vfio_pci_priv.h   | 14 ++++++++
 include/uapi/linux/vfio.h          | 27 ++++++++++++++
 4 files changed, 99 insertions(+), 1 deletion(-)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 064906b25467..dc9c6f479e2c 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -1575,6 +1575,8 @@ int vfio_pci_core_ioctl_feature(struct vfio_device *device, u32 flags,
 		return vfio_pci_core_feature_dma_buf(vdev, flags, arg, argsz);
 	case VFIO_DEVICE_FEATURE_DMA_BUF_REVOKE:
 		return vfio_pci_core_feature_dma_buf_revoke(vdev, flags, arg, argsz);
+	case VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR:
+		return vfio_pci_core_feature_dma_buf_memattr(vdev, flags, arg, argsz);
 	default:
 		return -ENOTTY;
 	}
diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index b47411992ab6..58b769e65ab8 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -51,7 +51,10 @@ static int vfio_pci_dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *
 	 * contained within the DMABUF size before calling this.
 	 */
 
-	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+	if (READ_ONCE(priv->memattr) == VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_WC)
+		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
+	else
+		vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 	vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
 
 	/* See comments in vfio_pci_core_mmap() re VM_ALLOW_ANY_UNCACHED. */
@@ -468,6 +471,7 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 	priv->vdev = vdev;
 	priv->nr_ranges = get_dma_buf.nr_ranges;
 	priv->size = length;
+	priv->memattr = VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_NC;
 	ret = vdev->pci_ops->get_dmabuf_phys(vdev, &priv->provider,
 					     get_dma_buf.region_index,
 					     priv->phys_vec, dma_ranges,
@@ -755,6 +759,57 @@ int vfio_pci_core_feature_dma_buf_revoke(
 		}
 	}
 
+out_put_buf:
+	dma_buf_put(dmabuf);
+
+	return ret;
+}
+
+int vfio_pci_core_feature_dma_buf_memattr(
+	struct vfio_pci_core_device *vdev, u32 flags,
+	struct vfio_device_feature_dma_buf_memattr __user *arg,
+	size_t argsz)
+{
+	struct vfio_device_feature_dma_buf_memattr db_attr;
+	struct vfio_pci_dma_buf *priv;
+	struct dma_buf *dmabuf;
+	int ret;
+
+	if (!vdev->pci_ops || !vdev->pci_ops->get_dmabuf_phys)
+		return -EOPNOTSUPP;
+
+	ret = vfio_check_feature(flags, argsz,
+				 VFIO_DEVICE_FEATURE_SET,
+				 sizeof(db_attr));
+	if (ret != 1)
+		return ret;
+
+	if (copy_from_user(&db_attr, arg, sizeof(db_attr)))
+		return -EFAULT;
+
+	dmabuf = dma_buf_get(db_attr.dmabuf_fd);
+	if (IS_ERR(dmabuf))
+		return PTR_ERR(dmabuf);
+
+	/* Verify DMABUF: see comments in vfio_pci_dma_buf_revoke() */
+	priv = dmabuf->priv;
+	if (dmabuf->ops != &vfio_pci_dmabuf_ops ||
+	    READ_ONCE(priv->vdev) != vdev) {
+		ret = -ENODEV;
+		goto out_put_buf;
+	}
+
+	switch (db_attr.memattr) {
+	case VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_NC:
+	case VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_WC:
+		WRITE_ONCE(priv->memattr, db_attr.memattr);
+		ret = 0;
+		break;
+
+	default:
+		ret = -ENOENT;
+	}
+
 out_put_buf:
 	dma_buf_put(dmabuf);
 
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index 3c2f2575b670..3ec8b62194f3 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -41,6 +41,7 @@ struct vfio_pci_dma_buf {
 	struct kref kref;
 	struct completion comp;
 	unsigned long vma_pgoff_adjust;
+	u32 memattr;
 	enum vfio_pci_dma_buf_status status;
 };
 
@@ -158,6 +159,10 @@ int vfio_pci_core_feature_dma_buf_revoke(
 	struct vfio_pci_core_device *vdev, u32 flags,
 	struct vfio_device_feature_dma_buf_revoke __user *arg,
 	size_t argsz);
+int vfio_pci_core_feature_dma_buf_memattr(
+	struct vfio_pci_core_device *vdev, u32 flags,
+	struct vfio_device_feature_dma_buf_memattr __user *arg,
+	size_t argsz);
 #else
 static inline int
 vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
@@ -166,6 +171,7 @@ vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 {
 	return -ENOTTY;
 }
+
 static inline int vfio_pci_core_feature_dma_buf_revoke(
 	struct vfio_pci_core_device *vdev, u32 flags,
 	struct vfio_device_feature_dma_buf_revoke __user *arg,
@@ -173,6 +179,14 @@ static inline int vfio_pci_core_feature_dma_buf_revoke(
 {
 	return -ENOTTY;
 }
+
+static inline int vfio_pci_core_feature_dma_buf_memattr(
+	struct vfio_pci_core_device *vdev, u32 flags,
+	struct vfio_device_feature_dma_buf_memattr __user *arg,
+	size_t argsz)
+{
+	return -ENOTTY;
+}
 #endif
 
 #endif
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 697c0bb4b9bc..ab30b89399d0 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -1554,6 +1554,33 @@ struct vfio_device_feature_dma_buf_revoke {
 	__s32	dmabuf_fd;
 };
 
+/**
+ * Given a dma_buf fd previously created by
+ * VFIO_DEVICE_FEATURE_DMA_BUF, SET the memory attribute that will be
+ * used by future mmap()s of that fd.  SETting a new attribute does
+ * not affect existing VMAs.
+ *
+ * The default, if no previous SET has been performed, is NC.
+ *
+ * Return: 0 on success, -1 and errno is set on failure:
+ *
+ *  EBADF, EINVAL: dmabuf_fd is not a DMABUF fd.
+ *  ENODEV: The dmabuf_fd does not match this VFIO device.
+ *  ENOENT: The given memattr is not supported.
+ */
+#define VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR 14
+
+/* Valid memory attributes for the memattr field */
+enum vfio_device_dma_buf_memattr {
+	VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_NC = 0, /* pgprot_noncached */
+	VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_WC = 1, /* pgprot_writecombine */
+};
+
+struct vfio_device_feature_dma_buf_memattr {
+	__s32	dmabuf_fd;
+	__u32	memattr;
+};
+
 /* -------- API for Type1 VFIO IOMMU -------- */
 
 /**
-- 
2.50.1 (Apple Git-155)

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

[Leon Romanovsky]

On Wed, Jun 10, 2026 at 04:43:15PM +0100, Matt Evans wrote:
> The P2PDMA code currently provides two features under the same
> CONFIG_PCI_P2PDMA option:
> 
>  1.  Locate providers via pcim_p2pdma_provider()
>  2.  Manage actual P2P DMA
> 
> Some drivers (such as vfio-pci) depend on 1, without having a hard
> dependency on 2.
> 
> A future commit expands the use of DMABUF in vfio-pci for non-P2P
> scenarios, relying on pcim_p2pdma_provider() always being present.  If
> that depended on CONFIG_PCI_P2PDMA, it would make vfio-pci only
> available if CONFIG_ZONE_DEVICE is present (e.g. 64-bit systems), even
> when P2P is not needed.
> 
> To resolve this, introduce CONFIG_PCI_P2PDMA_CORE and refactor the
> basic provider functionality into a new p2pdma_core.c file.  This is
> available even if the CONFIG_PCI_P2PDMA feature is disabled (or
> unavailable due to !CONFIG_ZONE_DEVICE).  Then, drivers can enable any
> additional P2P features with the original CONFIG_PCI_P2PDMA (available
> when CONFIG_ZONE_DEVICE is set).
> 
> Signed-off-by: Matt Evans <matt@ozlabs.org>
> ---
>  MAINTAINERS                |   2 +-
>  drivers/pci/Kconfig        |  10 ++--
>  drivers/pci/Makefile       |   1 +
>  drivers/pci/p2pdma.c       | 109 ++--------------------------------
>  drivers/pci/p2pdma.h       |  29 +++++++++
>  drivers/pci/p2pdma_core.c  | 118 +++++++++++++++++++++++++++++++++++++
>  include/linux/pci-p2pdma.h |  24 ++++----
>  include/linux/pci.h        |   2 +-
>  8 files changed, 174 insertions(+), 121 deletions(-)
>  create mode 100644 drivers/pci/p2pdma.h
>  create mode 100644 drivers/pci/p2pdma_core.c

Thanks,
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>

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

[Bjorn Helgaas]

On Wed, Jun 10, 2026 at 04:43:15PM +0100, Matt Evans wrote:
> The P2PDMA code currently provides two features under the same
> CONFIG_PCI_P2PDMA option:
> 
>  1.  Locate providers via pcim_p2pdma_provider()
>  2.  Manage actual P2P DMA
> 
> Some drivers (such as vfio-pci) depend on 1, without having a hard
> dependency on 2.
> 
> A future commit expands the use of DMABUF in vfio-pci for non-P2P
> scenarios, relying on pcim_p2pdma_provider() always being present.  If
> that depended on CONFIG_PCI_P2PDMA, it would make vfio-pci only
> available if CONFIG_ZONE_DEVICE is present (e.g. 64-bit systems), even
> when P2P is not needed.
> 
> To resolve this, introduce CONFIG_PCI_P2PDMA_CORE and refactor the
> basic provider functionality into a new p2pdma_core.c file.  This is
> available even if the CONFIG_PCI_P2PDMA feature is disabled (or
> unavailable due to !CONFIG_ZONE_DEVICE).  Then, drivers can enable any
> additional P2P features with the original CONFIG_PCI_P2PDMA (available
> when CONFIG_ZONE_DEVICE is set).
> 
> Signed-off-by: Matt Evans <matt@ozlabs.org>

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

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

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

> +++ b/drivers/pci/p2pdma.h
> @@ -0,0 +1,29 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * PCI Peer 2 Peer DMA support.
> + */
> +
> +#ifndef _PCI_P2PDMA_H
> +#define _PCI_P2PDMA_H
> +
> +#include <linux/genalloc.h>
> +#include <linux/pci-p2pdma.h>
> +#include <linux/xarray.h>
> +
> +struct pci_p2pdma {
> +	struct gen_pool *pool;
> +	bool p2pmem_published;
> +	struct xarray map_types;
> +	struct p2pdma_provider mem[PCI_STD_NUM_BARS];
> +};
> +
> +#ifdef CONFIG_PCI_P2PDMA
> +void pci_p2pdma_release_pool(struct pci_dev *pdev, struct pci_p2pdma *p2pdma);
> +#else
> +static inline void pci_p2pdma_release_pool(struct pci_dev *pdev, struct pci_p2pdma *p2pdma)

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

> +{
> +}
> +#endif
> +
> +#endif
> +

Spurious blank line at end.

> +++ b/drivers/pci/p2pdma_core.c
> @@ -0,0 +1,118 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * PCI Peer 2 Peer DMA support core, providing a bare-bones

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

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

[Matt Evans]

Hi Bjorn,

On 11/06/2026 17:07, Bjorn Helgaas wrote:
> On Wed, Jun 10, 2026 at 04:43:15PM +0100, Matt Evans wrote:
>> The P2PDMA code currently provides two features under the same
>> CONFIG_PCI_P2PDMA option:
>>
>>  1.  Locate providers via pcim_p2pdma_provider()
>>  2.  Manage actual P2P DMA
>>
>> Some drivers (such as vfio-pci) depend on 1, without having a hard
>> dependency on 2.
>>
>> A future commit expands the use of DMABUF in vfio-pci for non-P2P
>> scenarios, relying on pcim_p2pdma_provider() always being present.  If
>> that depended on CONFIG_PCI_P2PDMA, it would make vfio-pci only
>> available if CONFIG_ZONE_DEVICE is present (e.g. 64-bit systems), even
>> when P2P is not needed.
>>
>> To resolve this, introduce CONFIG_PCI_P2PDMA_CORE and refactor the
>> basic provider functionality into a new p2pdma_core.c file.  This is
>> available even if the CONFIG_PCI_P2PDMA feature is disabled (or
>> unavailable due to !CONFIG_ZONE_DEVICE).  Then, drivers can enable any
>> additional P2P features with the original CONFIG_PCI_P2PDMA (available
>> when CONFIG_ZONE_DEVICE is set).
>>
>> Signed-off-by: Matt Evans <matt@ozlabs.org>
> 
> I thought this was going to be just a code move and new Kconfig
> option, but it involves a little more than that, e.g., adding
> pci_p2pdma_release_pool() and tweaking the RCU synchronization.
> 
> If possible, it would be nice to do that refactoring in a smaller
> preliminary patch so it's easier to review/bisect/etc and make this
> one a pure code move.

pci_p2pdma_release_pool() is really part of the split, not a functional
change, i.e. factoring the (P2P-only) pool handling out from the rest of
the pci_p2pdma_release() actions still needed for the _CORE case.

I guess .._release() could be split in place in a small patch, and then
moved alongside the rest in a second.

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

Yes, I can reword that last paragraph of the commit message to make this
clearer.

>> +++ b/drivers/pci/p2pdma.h
>> @@ -0,0 +1,29 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/*
>> + * PCI Peer 2 Peer DMA support.
>> + */
>> +
>> +#ifndef _PCI_P2PDMA_H
>> +#define _PCI_P2PDMA_H
>> +
>> +#include <linux/genalloc.h>
>> +#include <linux/pci-p2pdma.h>
>> +#include <linux/xarray.h>
>> +
>> +struct pci_p2pdma {
>> +	struct gen_pool *pool;
>> +	bool p2pmem_published;
>> +	struct xarray map_types;
>> +	struct p2pdma_provider mem[PCI_STD_NUM_BARS];
>> +};
>> +
>> +#ifdef CONFIG_PCI_P2PDMA
>> +void pci_p2pdma_release_pool(struct pci_dev *pdev, struct pci_p2pdma *p2pdma);
>> +#else
>> +static inline void pci_p2pdma_release_pool(struct pci_dev *pdev, struct pci_p2pdma *p2pdma)
> 
> Wrap to fit in 80 columns like the rest of drivers/pci/

Fixed.

>> +{
>> +}
>> +#endif
>> +
>> +#endif
>> +
> 
> Spurious blank line at end.

Doh, fixed.

>> +++ b/drivers/pci/p2pdma_core.c
>> @@ -0,0 +1,118 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * PCI Peer 2 Peer DMA support core, providing a bare-bones
> 
> In this English text, I think I would spell out "Peer to Peer" instead
> of relying on the "2" homophone.  Same in p2pdma.h.

I would've preferred that too, it isn't correct; I was seeking to keep
the blurb here (and in p2pdma.h) as close to the original p2pdma.c as
possible.  I'll correct it in the new files (hyphenated "peer-to-peer"
in PCI-SIG language).


Thanks,


Matt

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

[Pranjal Shrivastava]

On Wed, Jun 10, 2026 at 04:43:15PM +0100, Matt Evans wrote:
> The P2PDMA code currently provides two features under the same
> CONFIG_PCI_P2PDMA option:
> 
>  1.  Locate providers via pcim_p2pdma_provider()
>  2.  Manage actual P2P DMA
> 
> Some drivers (such as vfio-pci) depend on 1, without having a hard
> dependency on 2.
> 
> A future commit expands the use of DMABUF in vfio-pci for non-P2P
> scenarios, relying on pcim_p2pdma_provider() always being present.  If
> that depended on CONFIG_PCI_P2PDMA, it would make vfio-pci only
> available if CONFIG_ZONE_DEVICE is present (e.g. 64-bit systems), even
> when P2P is not needed.
> 
> To resolve this, introduce CONFIG_PCI_P2PDMA_CORE and refactor the
> basic provider functionality into a new p2pdma_core.c file.  This is
> available even if the CONFIG_PCI_P2PDMA feature is disabled (or
> unavailable due to !CONFIG_ZONE_DEVICE).  Then, drivers can enable any
> additional P2P features with the original CONFIG_PCI_P2PDMA (available
> when CONFIG_ZONE_DEVICE is set).
> 
> Signed-off-by: Matt Evans <matt@ozlabs.org>
> ---
>  MAINTAINERS                |   2 +-
>  drivers/pci/Kconfig        |  10 ++--
>  drivers/pci/Makefile       |   1 +
>  drivers/pci/p2pdma.c       | 109 ++--------------------------------
>  drivers/pci/p2pdma.h       |  29 +++++++++
>  drivers/pci/p2pdma_core.c  | 118 +++++++++++++++++++++++++++++++++++++
>  include/linux/pci-p2pdma.h |  24 ++++----
>  include/linux/pci.h        |   2 +-
>  8 files changed, 174 insertions(+), 121 deletions(-)
>  create mode 100644 drivers/pci/p2pdma.h
>  create mode 100644 drivers/pci/p2pdma_core.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index c2c6d79275c6..b21523b3bd8b 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -20617,7 +20617,7 @@ B:	https://bugzilla.kernel.org
>  C:	irc://irc.oftc.net/linux-pci
>  T:	git git://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git
>  F:	Documentation/driver-api/pci/p2pdma.rst
> -F:	drivers/pci/p2pdma.c
> +F:	drivers/pci/p2pdma*
>  F:	include/linux/pci-p2pdma.h
>  
>  PCI POWER CONTROL
> diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
> index 33c88432b728..59d70bc84cc9 100644
> --- a/drivers/pci/Kconfig
> +++ b/drivers/pci/Kconfig
> @@ -206,11 +206,7 @@ config PCIE_TPH
>  config PCI_P2PDMA
>  	bool "PCI peer-to-peer transfer support"
>  	depends on ZONE_DEVICE
> -	#
> -	# The need for the scatterlist DMA bus address flag means PCI P2PDMA
> -	# requires 64bit
> -	#
> -	depends on 64BIT
> +	select PCI_P2PDMA_CORE
>  	select GENERIC_ALLOCATOR
>  	select NEED_SG_DMA_FLAGS
>  	help

Nit: Did we drop depends on 64BIT intentionally here? I guess the full
PCI_P2PDMA stack still selects NEED_SG_DMA_FLAGS? IIRC, NEED_SG_DMA_FLAGS
doesn't select 64BIT?

With the nit (and Bjorn's comments addressed)
Reviewed-by: Pranjal Shrivastava <praan@google.com>

Thanks,
Praan

Re: [PATCH v3 2/9] vfio/pci: Add a helper to look up PFNs for DMABUFs

[Pranjal Shrivastava]

On Wed, Jun 10, 2026 at 04:43:16PM +0100, Matt Evans wrote:
> Add vfio_pci_dma_buf_find_pfn(), which a VMA fault handler can use to
> find a PFN.
> 
> This supports multi-range DMABUFs, which typically would be used to
> represent scattered spans but might even represent overlapping or
> aliasing spans of PFNs.
> 
> Because this is intended to be used in vfio_pci_core.c, we also need
> to expose the struct vfio_pci_dma_buf in the vfio_pci_priv.h header.
> 
> Signed-off-by: Matt Evans <matt@ozlabs.org>
> ---
>  drivers/vfio/pci/vfio_pci_dmabuf.c | 137 ++++++++++++++++++++++++++---
>  drivers/vfio/pci/vfio_pci_priv.h   |  20 +++++
>  2 files changed, 144 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
> index c16f460c01d6..9e5e865f6fb6 100644
> --- a/drivers/vfio/pci/vfio_pci_dmabuf.c
> +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
> @@ -9,19 +9,6 @@
>  
>  MODULE_IMPORT_NS("DMA_BUF");
>  
> -struct vfio_pci_dma_buf {
> -	struct dma_buf *dmabuf;
> -	struct vfio_pci_core_device *vdev;
> -	struct list_head dmabufs_elm;
> -	size_t size;
> -	struct phys_vec *phys_vec;
> -	struct p2pdma_provider *provider;
> -	u32 nr_ranges;
> -	struct kref kref;
> -	struct completion comp;
> -	u8 revoked : 1;
> -};
> -
>  static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
>  				   struct dma_buf_attachment *attachment)
>  {
> @@ -106,6 +93,130 @@ static const struct dma_buf_ops vfio_pci_dmabuf_ops = {
>  	.release = vfio_pci_dma_buf_release,
>  };
>  
> +int vfio_pci_dma_buf_find_pfn(struct vfio_pci_dma_buf *priv,
> +			      struct vm_area_struct *vma,
> +			      unsigned long address,

Nit: s/address/fault_addr ?

> +			      unsigned int order,
> +			      unsigned long *out_pfn)
> +{
> +	/*
> +	 * Given a VMA (start, end, pgoffs) and a fault address,
> +	 * search the corresponding DMABUF's phys_vec[] to find the
> +	 * range representing the address's offset into the VMA, and
> +	 * its PFN.
> +	 *
> +	 * The phys_vec[] ranges represent contiguous spans of VAs
> +	 * upwards from the buffer offset 0; the actual PFNs might be
> +	 * in any order, overlap/alias, etc.  Calculate an offset of
> +	 * the desired page given VMA start/pgoff and address, then
> +	 * search upwards from 0 to find which span contains it.
> +	 *
> +	 * On success, a valid PFN for a page sized by 'order' is
> +	 * returned into out_pfn.
> +	 *
> +	 * Failure occurs if:
> +	 * - The page would cross the edge of the VMA
> +	 * - The page isn't entirely contained within a range
> +	 * - We find a range, but the final PFN isn't aligned to the
> +	 *   requested order.
> +	 *
> +	 * (Upon failure, the caller is expected to try again with a
> +	 * smaller order; the tests above will always succeed for
> +	 * order=0 as the limit case.)
> +	 *
> +	 * It's suboptimal if DMABUFs are created with neigbouring
> +	 * ranges that are physically contiguous, since hugepages
> +	 * can't straddle range boundaries.  (The construction of the
> +	 * ranges vector should merge such ranges.)
> +	 *
> +	 * Finally, vma_pgoff_adjust is used for a DMABUF representing
> +	 * a VFIO BAR mmap, which is created from the start of the
> +	 * offset region.
> +	 */
> +
> +	const unsigned long pagesize = PAGE_SIZE << order;
> +	unsigned long vma_off = ((vma->vm_pgoff - priv->vma_pgoff_adjust) <<
> +				 PAGE_SHIFT) & VFIO_PCI_OFFSET_MASK;
> +	unsigned long rounded_page_addr = ALIGN_DOWN(address, pagesize);
> +	unsigned long rounded_page_end = rounded_page_addr + pagesize;
> +	unsigned long page_buf_offset;
> +	unsigned long page_buf_offset_end;
> +	unsigned long range_buf_offset = 0;
> +	unsigned int i;
> +
> +	if (rounded_page_addr < vma->vm_start || rounded_page_end > vma->vm_end) {
> +		if (order > 0)
> +			return -EAGAIN;
> +
> +		/* A fault address outside of the VMA is absurd. */
> +		WARN(1, "Fault addr 0x%lx outside VMA 0x%lx-0x%lx\n",
> +		     address, vma->vm_start, vma->vm_end);

This could flood dmesg if triggered repeatedly by userspace :( 
Since a fault outside the VMA is an invalid access that already results
in a SIGBUS, we could probably avoid the WARN here?
Perhaps pr_warn_ratelimited() should suffice?

> +		return -EFAULT;
> +	}
> +
> +	/*
> +	 * page_buff_offset[_end] is the span of DMABUF offsets
> +	 * corresponding to the faulting page:
> +	 */
> +	if (unlikely(check_add_overflow(rounded_page_addr - vma->vm_start,
> +					vma_off, &page_buf_offset) ||
> +		     check_add_overflow(page_buf_offset, pagesize,
> +					&page_buf_offset_end)))
> +		return -EFAULT;
> +
> +	for (i = 0; i < priv->nr_ranges; i++) {
> +		size_t range_len = priv->phys_vec[i].len;
> +		phys_addr_t range_start = priv->phys_vec[i].paddr;
> +
> +		/*
> +		 * If the current range starts after the page's span,
> +		 * this and any future range won't match.  Bail early.
> +		 */
> +		if (page_buf_offset_end <= range_buf_offset)
> +			break;
> +
> +		if (page_buf_offset >= range_buf_offset &&
> +		    page_buf_offset_end <= range_buf_offset + range_len) {
> +			/*
> +			 * The faulting page is wholly contained
> +			 * within the span represented by the range.
> +			 * Validate PFN alignment for the order:
> +			 */
> +			unsigned long pfn = (range_start + page_buf_offset -
> +					     range_buf_offset) / PAGE_SIZE;

Minor nit: I'm aware that decent compilers convert pow(2) divides to >> 
However, we seem to be using `>> PAGE_SHIFT` across vfio-pci. E.g.:

return (pci_resource_start(vdev->pdev, index) >> PAGE_SHIFT) + pgoff;
unsigned long pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;

Let's consider using the same pattern?

> +
> +			if (IS_ALIGNED(pfn, 1 << order)) {
> +				*out_pfn = pfn;
> +				return 0;
> +			}
> +			/* Retry with smaller order */
> +			return -EAGAIN;
> +		}
> +		range_buf_offset += range_len;
> +	}
> +
> +	/*
> +	 * A hugepage straddling a range boundary will fail to match a
> +	 * range, but the address will (eventually) match when retried
> +	 * with a smaller page.
> +	 */
> +	if (order > 0)
> +		return -EAGAIN;
> +
> +	/*
> +	 * If we get here, the address fell outside of the span
> +	 * represented by the (concatenated) ranges.  Setup of a

Nit: double space before "Setup" and "But" below.

> +	 * mapping must ensure that the VMA is <= the total size of
> +	 * the ranges, so this should never happen.  But, if it does,
> +	 * force SIGBUS for the access and warn.
> +	 */
> +	WARN_ONCE(1, "No range for addr 0x%lx, order %d: VMA 0x%lx-0x%lx pgoff 0x%lx, %u ranges, size 0x%zx\n",
> +		  address, order, vma->vm_start, vma->vm_end, vma->vm_pgoff,
> +		  priv->nr_ranges, priv->size);
> +
> +	return -EFAULT;

The fall-through logic at the end feels a bit redundant.

If we've exhausted the phys_vec list without finding a match, returning
-EAGAIN for order > 0 seems like the correct fallback behavior.

However, the subsequent WARN_ONCE for the order == 0 seems unnecessary?
An out-of-bounds access is an error that should simply return -EFAULT 
(converting to SIGBUS) without polluting the kernel log with stackdumps?
Can we instead convert this to a pr_warn or something? Something like:

	ret = order ? -EAGAIN : -EFAULT;

	if (ret == -EFAULT)
		pr_warn_ratelimited("No range for addr 0x%lx...\n", address);

	return ret;

(with appropriate comments)

Thanks,
Praan