[PATCH kernel v7 20/20] vfio_pci: Add NVIDIA GV100GL [Tesla V100 SXM2] subdriver

[Alexey Kardashevskiy]

POWER9 Witherspoon machines come with 4 or 6 V100 GPUs which are not
pluggable PCIe devices but still have PCIe links which are used
for config space and MMIO. In addition to that the GPUs have 6 NVLinks
which are connected to other GPUs and the POWER9 CPU. POWER9 chips
have a special unit on a die called an NPU which is an NVLink2 host bus
adapter with p2p connections to 2 to 3 GPUs, 3 or 2 NVLinks to each.
These systems also support ATS (address translation services) which is
a part of the NVLink2 protocol. Such GPUs also share on-board RAM
(16GB or 32GB) to the system via the same NVLink2 so a CPU has
cache-coherent access to a GPU RAM.

This exports GPU RAM to the userspace as a new VFIO device region. This
preregisters the new memory as device memory as it might be used for DMA.
This inserts pfns from the fault handler as the GPU memory is not onlined
until the vendor driver is loaded and trained the NVLinks so doing this
earlier causes low level errors which we fence in the firmware so
it does not hurt the host system but still better be avoided; for the same
reason this does not map GPU RAM into the host kernel (usual thing for
emulated access otherwise).

This exports an ATSD (Address Translation Shootdown) register of NPU which
allows TLB invalidations inside GPU for an operating system. The register
conveniently occupies a single 64k page. It is also presented to
the userspace as a new VFIO device region. One NPU has 8 ATSD registers,
each of them can be used for TLB invalidation in a GPU linked to this NPU.
This allocates one ATSD register per an NVLink bridge allowing passing
up to 6 registers. Due to the host firmware bug (just recently fixed),
only 1 ATSD register per NPU was actually advertised to the host system
so this passes that alone register via the first NVLink bridge device in
the group which is still enough as QEMU collects them all back and
presents to the guest via vPHB to mimic the emulated NPU PHB on the host.

In order to provide the userspace with the information about GPU-to-NVLink
connections, this exports an additional capability called "tgt"
(which is an abbreviated host system bus address). The "tgt" property
tells the GPU its own system address and allows the guest driver to
conglomerate the routing information so each GPU knows how to get directly
to the other GPUs.

For ATS to work, the nest MMU (an NVIDIA block in a P9 CPU) needs to
know LPID (a logical partition ID or a KVM guest hardware ID in other
words) and PID (a memory context ID of a userspace process, not to be
confused with a linux pid). This assigns a GPU to LPID in the NPU and
this is why this adds a listener for KVM on an IOMMU group. A PID comes
via NVLink from a GPU and NPU uses a PID wildcard to pass it through.

This requires coherent memory and ATSD to be available on the host as
the GPU vendor only supports configurations with both features enabled
and other configurations are known not to work. Because of this and
because of the ways the features are advertised to the host system
(which is a device tree with very platform specific properties),
this requires enabled POWERNV platform.

The V100 GPUs do not advertise any of these capabilities via the config
space and there are more than just one device ID so this relies on
the platform to tell whether these GPUs have special abilities such as
NVLinks.

Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
---
Changes:
v6.1:
* fixed outdated comment about VFIO_REGION_INFO_CAP_NVLINK2_LNKSPD

v6:
* reworked capabilities - tgt for nvlink and gpu and link-speed
for nvlink only

v5:
* do not memremap GPU RAM for emulation, map it only when it is needed
* allocate 1 ATSD register per NVLink bridge, if none left, then expose
the region with a zero size
* separate caps per device type
* addressed AW review comments

v4:
* added nvlink-speed to the NPU bridge capability as this turned out to
be not a constant value
* instead of looking at the exact device ID (which also changes from system
to system), now this (indirectly) looks at the device tree to know
if GPU and NPU support NVLink

v3:
* reworded the commit log about tgt
* added tracepoints (do we want them enabled for entire vfio-pci?)
* added code comments
* added write|mmap flags to the new regions
* auto enabled VFIO_PCI_NVLINK2 config option
* added 'tgt' capability to a GPU so QEMU can recreate ibm,npu and ibm,gpu
references; there are required by the NVIDIA driver
* keep notifier registered only for short time
---
 drivers/vfio/pci/Makefile           |   1 +
 drivers/vfio/pci/trace.h            | 102 ++++++
 drivers/vfio/pci/vfio_pci_private.h |  14 +
 include/uapi/linux/vfio.h           |  37 +++
 drivers/vfio/pci/vfio_pci.c         |  27 +-
 drivers/vfio/pci/vfio_pci_nvlink2.c | 482 ++++++++++++++++++++++++++++
 drivers/vfio/pci/Kconfig            |   6 +
 7 files changed, 667 insertions(+), 2 deletions(-)
 create mode 100644 drivers/vfio/pci/trace.h
 create mode 100644 drivers/vfio/pci/vfio_pci_nvlink2.c

diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
index 76d8ec0..9662c06 100644
--- a/drivers/vfio/pci/Makefile
+++ b/drivers/vfio/pci/Makefile
@@ -1,5 +1,6 @@
 
 vfio-pci-y := vfio_pci.o vfio_pci_intrs.o vfio_pci_rdwr.o vfio_pci_config.o
 vfio-pci-$(CONFIG_VFIO_PCI_IGD) += vfio_pci_igd.o
+vfio-pci-$(CONFIG_VFIO_PCI_NVLINK2) += vfio_pci_nvlink2.o
 
 obj-$(CONFIG_VFIO_PCI) += vfio-pci.o
diff --git a/drivers/vfio/pci/trace.h b/drivers/vfio/pci/trace.h
new file mode 100644
index 0000000..b80d2d3
--- /dev/null
+++ b/drivers/vfio/pci/trace.h
@@ -0,0 +1,102 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * VFIO PCI mmap/mmap_fault tracepoints
+ *
+ * Copyright (C) 2018 IBM Corp.  All rights reserved.
+ *     Author: Alexey Kardashevskiy <aik@xxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM vfio_pci
+
+#if !defined(_TRACE_VFIO_PCI_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_VFIO_PCI_H
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(vfio_pci_nvgpu_mmap_fault,
+	TP_PROTO(struct pci_dev *pdev, unsigned long hpa, unsigned long ua,
+			vm_fault_t ret),
+	TP_ARGS(pdev, hpa, ua, ret),
+
+	TP_STRUCT__entry(
+		__field(const char *, name)
+		__field(unsigned long, hpa)
+		__field(unsigned long, ua)
+		__field(int, ret)
+	),
+
+	TP_fast_assign(
+		__entry->name = dev_name(&pdev->dev),
+		__entry->hpa = hpa;
+		__entry->ua = ua;
+		__entry->ret = ret;
+	),
+
+	TP_printk("%s: %lx -> %lx ret=%d", __entry->name, __entry->hpa,
+			__entry->ua, __entry->ret)
+);
+
+TRACE_EVENT(vfio_pci_nvgpu_mmap,
+	TP_PROTO(struct pci_dev *pdev, unsigned long hpa, unsigned long ua,
+			unsigned long size, int ret),
+	TP_ARGS(pdev, hpa, ua, size, ret),
+
+	TP_STRUCT__entry(
+		__field(const char *, name)
+		__field(unsigned long, hpa)
+		__field(unsigned long, ua)
+		__field(unsigned long, size)
+		__field(int, ret)
+	),
+
+	TP_fast_assign(
+		__entry->name = dev_name(&pdev->dev),
+		__entry->hpa = hpa;
+		__entry->ua = ua;
+		__entry->size = size;
+		__entry->ret = ret;
+	),
+
+	TP_printk("%s: %lx -> %lx size=%lx ret=%d", __entry->name, __entry->hpa,
+			__entry->ua, __entry->size, __entry->ret)
+);
+
+TRACE_EVENT(vfio_pci_npu2_mmap,
+	TP_PROTO(struct pci_dev *pdev, unsigned long hpa, unsigned long ua,
+			unsigned long size, int ret),
+	TP_ARGS(pdev, hpa, ua, size, ret),
+
+	TP_STRUCT__entry(
+		__field(const char *, name)
+		__field(unsigned long, hpa)
+		__field(unsigned long, ua)
+		__field(unsigned long, size)
+		__field(int, ret)
+	),
+
+	TP_fast_assign(
+		__entry->name = dev_name(&pdev->dev),
+		__entry->hpa = hpa;
+		__entry->ua = ua;
+		__entry->size = size;
+		__entry->ret = ret;
+	),
+
+	TP_printk("%s: %lx -> %lx size=%lx ret=%d", __entry->name, __entry->hpa,
+			__entry->ua, __entry->size, __entry->ret)
+);
+
+#endif /* _TRACE_SUBSYS_H */
+
+#undef TRACE_INCLUDE_PATH
+#define TRACE_INCLUDE_PATH .
+#undef TRACE_INCLUDE_FILE
+#define TRACE_INCLUDE_FILE trace
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
index 93c1738..127071b 100644
--- a/drivers/vfio/pci/vfio_pci_private.h
+++ b/drivers/vfio/pci/vfio_pci_private.h
@@ -163,4 +163,18 @@ static inline int vfio_pci_igd_init(struct vfio_pci_device *vdev)
 	return -ENODEV;
 }
 #endif
+#ifdef CONFIG_VFIO_PCI_NVLINK2
+extern int vfio_pci_nvdia_v100_nvlink2_init(struct vfio_pci_device *vdev);
+extern int vfio_pci_ibm_npu2_init(struct vfio_pci_device *vdev);
+#else
+static inline int vfio_pci_nvdia_v100_nvlink2_init(struct vfio_pci_device *vdev)
+{
+	return -ENODEV;
+}
+
+static inline int vfio_pci_ibm_npu2_init(struct vfio_pci_device *vdev)
+{
+	return -ENODEV;
+}
+#endif
 #endif /* VFIO_PCI_PRIVATE_H */
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 8131028..5562587 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -353,6 +353,21 @@ struct vfio_region_gfx_edid {
 #define VFIO_DEVICE_GFX_LINK_STATE_DOWN  2
 };
 
+/*
+ * 10de vendor sub-type
+ *
+ * NVIDIA GPU NVlink2 RAM is coherent RAM mapped onto the host address space.
+ */
+#define VFIO_REGION_SUBTYPE_NVIDIA_NVLINK2_RAM	(1)
+
+/*
+ * 1014 vendor sub-type
+ *
+ * IBM NPU NVlink2 ATSD (Address Translation Shootdown) register of NPU
+ * to do TLB invalidation on a GPU.
+ */
+#define VFIO_REGION_SUBTYPE_IBM_NVLINK2_ATSD	(1)
+
 /*
  * The MSIX mappable capability informs that MSIX data of a BAR can be mmapped
  * which allows direct access to non-MSIX registers which happened to be within
@@ -363,6 +378,28 @@ struct vfio_region_gfx_edid {
  */
 #define VFIO_REGION_INFO_CAP_MSIX_MAPPABLE	3
 
+/*
+ * Capability with compressed real address (aka SSA - small system address)
+ * where GPU RAM is mapped on a system bus. Used by a GPU for DMA routing.
+ */
+#define VFIO_REGION_INFO_CAP_NVLINK2_SSATGT	4
+
+struct vfio_region_info_cap_nvlink2_ssatgt {
+	struct vfio_info_cap_header header;
+	__u64 tgt;
+};
+
+/*
+ * Capability with an NVLink link speed.
+ */
+#define VFIO_REGION_INFO_CAP_NVLINK2_LNKSPD	5
+
+struct vfio_region_info_cap_nvlink2_lnkspd {
+	struct vfio_info_cap_header header;
+	__u32 link_speed;
+	__u32 __pad;
+};
+
 /**
  * VFIO_DEVICE_GET_IRQ_INFO - _IOWR(VFIO_TYPE, VFIO_BASE + 9,
  *				    struct vfio_irq_info)
diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 6cb70cf..67c03f2 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -302,14 +302,37 @@ static int vfio_pci_enable(struct vfio_pci_device *vdev)
 		if (ret) {
 			dev_warn(&vdev->pdev->dev,
 				 "Failed to setup Intel IGD regions\n");
-			vfio_pci_disable(vdev);
-			return ret;
+			goto disable_exit;
+		}
+	}
+
+	if (pdev->vendor == PCI_VENDOR_ID_NVIDIA &&
+	    IS_ENABLED(CONFIG_VFIO_PCI_NVLINK2)) {
+		ret = vfio_pci_nvdia_v100_nvlink2_init(vdev);
+		if (ret && ret != -ENODEV) {
+			dev_warn(&vdev->pdev->dev,
+				 "Failed to setup NVIDIA NV2 RAM region\n");
+			goto disable_exit;
+		}
+	}
+
+	if (pdev->vendor == PCI_VENDOR_ID_IBM &&
+	    IS_ENABLED(CONFIG_VFIO_PCI_NVLINK2)) {
+		ret = vfio_pci_ibm_npu2_init(vdev);
+		if (ret && ret != -ENODEV) {
+			dev_warn(&vdev->pdev->dev,
+					"Failed to setup NVIDIA NV2 ATSD region\n");
+			goto disable_exit;
 		}
 	}
 
 	vfio_pci_probe_mmaps(vdev);
 
 	return 0;
+
+disable_exit:
+	vfio_pci_disable(vdev);
+	return ret;
 }
 
 static void vfio_pci_disable(struct vfio_pci_device *vdev)
diff --git a/drivers/vfio/pci/vfio_pci_nvlink2.c b/drivers/vfio/pci/vfio_pci_nvlink2.c
new file mode 100644
index 0000000..054a2cf
--- /dev/null
+++ b/drivers/vfio/pci/vfio_pci_nvlink2.c
@@ -0,0 +1,482 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * VFIO PCI NVIDIA Whitherspoon GPU support a.k.a. NVLink2.
+ *
+ * Copyright (C) 2018 IBM Corp.  All rights reserved.
+ *     Author: Alexey Kardashevskiy <aik@xxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Register an on-GPU RAM region for cacheable access.
+ *
+ * Derived from original vfio_pci_igd.c:
+ * Copyright (C) 2016 Red Hat, Inc.  All rights reserved.
+ *	Author: Alex Williamson <alex.williamson@xxxxxxxxxx>
+ */
+
+#include <linux/io.h>
+#include <linux/pci.h>
+#include <linux/uaccess.h>
+#include <linux/vfio.h>
+#include <linux/sched/mm.h>
+#include <linux/mmu_context.h>
+#include <asm/kvm_ppc.h>
+#include "vfio_pci_private.h"
+
+#define CREATE_TRACE_POINTS
+#include "trace.h"
+
+EXPORT_TRACEPOINT_SYMBOL_GPL(vfio_pci_nvgpu_mmap_fault);
+EXPORT_TRACEPOINT_SYMBOL_GPL(vfio_pci_nvgpu_mmap);
+EXPORT_TRACEPOINT_SYMBOL_GPL(vfio_pci_npu2_mmap);
+
+struct vfio_pci_nvgpu_data {
+	unsigned long gpu_hpa; /* GPU RAM physical address */
+	unsigned long gpu_tgt; /* TGT address of corresponding GPU RAM */
+	unsigned long useraddr; /* GPU RAM userspace address */
+	unsigned long size; /* Size of the GPU RAM window (usually 128GB) */
+	struct mm_struct *mm;
+	struct mm_iommu_table_group_mem_t *mem; /* Pre-registered RAM descr. */
+	struct pci_dev *gpdev;
+	struct notifier_block group_notifier;
+};
+
+static size_t vfio_pci_nvgpu_rw(struct vfio_pci_device *vdev,
+		char __user *buf, size_t count, loff_t *ppos, bool iswrite)
+{
+	unsigned int i = VFIO_PCI_OFFSET_TO_INDEX(*ppos) - VFIO_PCI_NUM_REGIONS;
+	struct vfio_pci_nvgpu_data *data = vdev->region[i].data;
+	loff_t pos = *ppos & VFIO_PCI_OFFSET_MASK;
+	loff_t posaligned = pos & PAGE_MASK, posoff = pos & ~PAGE_MASK;
+	size_t sizealigned;
+	void __iomem *ptr;
+
+	if (pos >= vdev->region[i].size)
+		return -EINVAL;
+
+	count = min(count, (size_t)(vdev->region[i].size - pos));
+
+	/*
+	 * We map only a bit of GPU RAM for a short time instead of mapping it
+	 * for the guest lifetime as:
+	 *
+	 * 1) we do not know GPU RAM size, only aperture which is 4-8 times
+	 *    bigger than actual RAM size (16/32GB RAM vs. 128GB aperture);
+	 * 2) mapping GPU RAM allows CPU to prefetch and if this happens
+	 *    before NVLink bridge is reset (which fences GPU RAM),
+	 *    hardware management interrupts (HMI) might happen, this
+	 *    will freeze NVLink bridge.
+	 *
+	 * This is not fast path anyway.
+	 */
+	sizealigned = _ALIGN_UP(posoff + count, PAGE_SIZE);
+	ptr = ioremap_cache(data->gpu_hpa + posaligned, sizealigned);
+	if (!ptr)
+		return -EFAULT;
+
+	if (iswrite) {
+		if (copy_from_user(ptr + posoff, buf, count))
+			count = -EFAULT;
+		else
+			*ppos += count;
+	} else {
+		if (copy_to_user(buf, ptr + posoff, count))
+			count = -EFAULT;
+		else
+			*ppos += count;
+	}
+
+	iounmap(ptr);
+
+	return count;
+}
+
+static void vfio_pci_nvgpu_release(struct vfio_pci_device *vdev,
+		struct vfio_pci_region *region)
+{
+	struct vfio_pci_nvgpu_data *data = region->data;
+	long ret;
+
+	/* If there were any mappings at all... */
+	if (data->mm) {
+		ret = mm_iommu_put(data->mm, data->mem);
+		WARN_ON(ret);
+
+		mmdrop(data->mm);
+	}
+
+	vfio_unregister_notifier(&data->gpdev->dev, VFIO_GROUP_NOTIFY,
+			&data->group_notifier);
+
+	pnv_npu2_unmap_lpar_dev(data->gpdev);
+
+	kfree(data);
+}
+
+static vm_fault_t vfio_pci_nvgpu_mmap_fault(struct vm_fault *vmf)
+{
+	vm_fault_t ret;
+	struct vm_area_struct *vma = vmf->vma;
+	struct vfio_pci_region *region = vma->vm_private_data;
+	struct vfio_pci_nvgpu_data *data = region->data;
+	unsigned long vmf_off = (vmf->address - vma->vm_start) >> PAGE_SHIFT;
+	unsigned long nv2pg = data->gpu_hpa >> PAGE_SHIFT;
+	unsigned long vm_pgoff = vma->vm_pgoff &
+		((1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) - 1);
+	unsigned long pfn = nv2pg + vm_pgoff + vmf_off;
+
+	ret = vmf_insert_pfn(vma, vmf->address, pfn);
+	trace_vfio_pci_nvgpu_mmap_fault(data->gpdev, pfn << PAGE_SHIFT,
+			vmf->address, ret);
+
+	return ret;
+}
+
+static const struct vm_operations_struct vfio_pci_nvgpu_mmap_vmops = {
+	.fault = vfio_pci_nvgpu_mmap_fault,
+};
+
+static int vfio_pci_nvgpu_mmap(struct vfio_pci_device *vdev,
+		struct vfio_pci_region *region, struct vm_area_struct *vma)
+{
+	int ret;
+	struct vfio_pci_nvgpu_data *data = region->data;
+
+	if (data->useraddr)
+		return -EPERM;
+
+	if (vma->vm_end - vma->vm_start > data->size)
+		return -EINVAL;
+
+	vma->vm_private_data = region;
+	vma->vm_flags |= VM_PFNMAP;
+	vma->vm_ops = &vfio_pci_nvgpu_mmap_vmops;
+
+	/*
+	 * Calling mm_iommu_newdev() here once as the region is not
+	 * registered yet and therefore right initialization will happen now.
+	 * Other places will use mm_iommu_find() which returns
+	 * registered @mem and does not go gup().
+	 */
+	data->useraddr = vma->vm_start;
+	data->mm = current->mm;
+
+	atomic_inc(&data->mm->mm_count);
+	ret = (int) mm_iommu_newdev(data->mm, data->useraddr,
+			(vma->vm_end - vma->vm_start) >> PAGE_SHIFT,
+			data->gpu_hpa, &data->mem);
+
+	trace_vfio_pci_nvgpu_mmap(vdev->pdev, data->gpu_hpa, data->useraddr,
+			vma->vm_end - vma->vm_start, ret);
+
+	return ret;
+}
+
+static int vfio_pci_nvgpu_add_capability(struct vfio_pci_device *vdev,
+		struct vfio_pci_region *region, struct vfio_info_cap *caps)
+{
+	struct vfio_pci_nvgpu_data *data = region->data;
+	struct vfio_region_info_cap_nvlink2_ssatgt cap = { 0 };
+
+	cap.header.id = VFIO_REGION_INFO_CAP_NVLINK2_SSATGT;
+	cap.header.version = 1;
+	cap.tgt = data->gpu_tgt;
+
+	return vfio_info_add_capability(caps, &cap.header, sizeof(cap));
+}
+
+static const struct vfio_pci_regops vfio_pci_nvgpu_regops = {
+	.rw = vfio_pci_nvgpu_rw,
+	.release = vfio_pci_nvgpu_release,
+	.mmap = vfio_pci_nvgpu_mmap,
+	.add_capability = vfio_pci_nvgpu_add_capability,
+};
+
+static int vfio_pci_nvgpu_group_notifier(struct notifier_block *nb,
+		unsigned long action, void *opaque)
+{
+	struct kvm *kvm = opaque;
+	struct vfio_pci_nvgpu_data *data = container_of(nb,
+			struct vfio_pci_nvgpu_data,
+			group_notifier);
+
+	if (action == VFIO_GROUP_NOTIFY_SET_KVM && kvm &&
+			pnv_npu2_map_lpar_dev(data->gpdev,
+				kvm->arch.lpid, MSR_DR | MSR_PR))
+		return NOTIFY_BAD;
+
+	return NOTIFY_OK;
+}
+
+int vfio_pci_nvdia_v100_nvlink2_init(struct vfio_pci_device *vdev)
+{
+	int ret;
+	u64 reg[2];
+	u64 tgt = 0;
+	struct device_node *npu_node, *mem_node;
+	struct pci_dev *npu_dev;
+	struct vfio_pci_nvgpu_data *data;
+	uint32_t mem_phandle = 0;
+	unsigned long events = VFIO_GROUP_NOTIFY_SET_KVM;
+
+	/*
+	 * PCI config space does not tell us about NVLink presense but
+	 * platform does, use this.
+	 */
+	npu_dev = pnv_pci_get_npu_dev(vdev->pdev, 0);
+	if (!npu_dev)
+		return -ENODEV;
+
+	npu_node = pci_device_to_OF_node(npu_dev);
+	if (!npu_node)
+		return -EINVAL;
+
+	if (of_property_read_u32(npu_node, "memory-region", &mem_phandle))
+		return -EINVAL;
+
+	mem_node = of_find_node_by_phandle(mem_phandle);
+	if (!mem_node)
+		return -EINVAL;
+
+	if (of_property_read_variable_u64_array(mem_node, "reg", reg,
+				ARRAY_SIZE(reg), ARRAY_SIZE(reg)) !=
+			ARRAY_SIZE(reg))
+		return -EINVAL;
+
+	if (of_property_read_u64(npu_node, "ibm,device-tgt-addr", &tgt)) {
+		dev_warn(&vdev->pdev->dev, "No ibm,device-tgt-addr found\n");
+		return -EFAULT;
+	}
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->gpu_hpa = reg[0];
+	data->gpu_tgt = tgt;
+	data->size = reg[1];
+
+	dev_dbg(&vdev->pdev->dev, "%lx..%lx\n", data->gpu_hpa,
+			data->gpu_hpa + data->size - 1);
+
+	data->gpdev = vdev->pdev;
+	data->group_notifier.notifier_call = vfio_pci_nvgpu_group_notifier;
+
+	ret = vfio_register_notifier(&data->gpdev->dev, VFIO_GROUP_NOTIFY,
+			&events, &data->group_notifier);
+	if (ret)
+		goto free_exit;
+
+	/*
+	 * We have just set KVM, we do not need the listener anymore.
+	 * Also, keeping it registered means that if more than one GPU is
+	 * assigned, we will get several similar notifiers notifying about
+	 * the same device again which does not help with anything.
+	 */
+	vfio_unregister_notifier(&data->gpdev->dev, VFIO_GROUP_NOTIFY,
+			&data->group_notifier);
+
+	ret = vfio_pci_register_dev_region(vdev,
+			PCI_VENDOR_ID_NVIDIA | VFIO_REGION_TYPE_PCI_VENDOR_TYPE,
+			VFIO_REGION_SUBTYPE_NVIDIA_NVLINK2_RAM,
+			&vfio_pci_nvgpu_regops,
+			data->size,
+			VFIO_REGION_INFO_FLAG_READ |
+			VFIO_REGION_INFO_FLAG_WRITE |
+			VFIO_REGION_INFO_FLAG_MMAP,
+			data);
+	if (ret)
+		goto free_exit;
+
+	return 0;
+free_exit:
+	kfree(data);
+
+	return ret;
+}
+
+/*
+ * IBM NPU2 bridge
+ */
+struct vfio_pci_npu2_data {
+	void *base; /* ATSD register virtual address, for emulated access */
+	unsigned long mmio_atsd; /* ATSD physical address */
+	unsigned long gpu_tgt; /* TGT address of corresponding GPU RAM */
+	unsigned int link_speed; /* The link speed from DT's ibm,nvlink-speed */
+};
+
+static size_t vfio_pci_npu2_rw(struct vfio_pci_device *vdev,
+		char __user *buf, size_t count, loff_t *ppos, bool iswrite)
+{
+	unsigned int i = VFIO_PCI_OFFSET_TO_INDEX(*ppos) - VFIO_PCI_NUM_REGIONS;
+	struct vfio_pci_npu2_data *data = vdev->region[i].data;
+	loff_t pos = *ppos & VFIO_PCI_OFFSET_MASK;
+
+	if (pos >= vdev->region[i].size)
+		return -EINVAL;
+
+	count = min(count, (size_t)(vdev->region[i].size - pos));
+
+	if (iswrite) {
+		if (copy_from_user(data->base + pos, buf, count))
+			return -EFAULT;
+	} else {
+		if (copy_to_user(buf, data->base + pos, count))
+			return -EFAULT;
+	}
+	*ppos += count;
+
+	return count;
+}
+
+static int vfio_pci_npu2_mmap(struct vfio_pci_device *vdev,
+		struct vfio_pci_region *region, struct vm_area_struct *vma)
+{
+	int ret;
+	struct vfio_pci_npu2_data *data = region->data;
+	unsigned long req_len = vma->vm_end - vma->vm_start;
+
+	if (req_len != PAGE_SIZE)
+		return -EINVAL;
+
+	vma->vm_flags |= VM_PFNMAP;
+	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+
+	ret = remap_pfn_range(vma, vma->vm_start, data->mmio_atsd >> PAGE_SHIFT,
+			req_len, vma->vm_page_prot);
+	trace_vfio_pci_npu2_mmap(vdev->pdev, data->mmio_atsd, vma->vm_start,
+			vma->vm_end - vma->vm_start, ret);
+
+	return ret;
+}
+
+static void vfio_pci_npu2_release(struct vfio_pci_device *vdev,
+		struct vfio_pci_region *region)
+{
+	struct vfio_pci_npu2_data *data = region->data;
+
+	memunmap(data->base);
+	kfree(data);
+}
+
+static int vfio_pci_npu2_add_capability(struct vfio_pci_device *vdev,
+		struct vfio_pci_region *region, struct vfio_info_cap *caps)
+{
+	struct vfio_pci_npu2_data *data = region->data;
+	struct vfio_region_info_cap_nvlink2_ssatgt captgt = { 0 };
+	struct vfio_region_info_cap_nvlink2_lnkspd capspd = { 0 };
+	int ret;
+
+	captgt.header.id = VFIO_REGION_INFO_CAP_NVLINK2_SSATGT;
+	captgt.header.version = 1;
+	captgt.tgt = data->gpu_tgt;
+
+	capspd.header.id = VFIO_REGION_INFO_CAP_NVLINK2_LNKSPD;
+	capspd.header.version = 1;
+	capspd.link_speed = data->link_speed;
+
+	ret = vfio_info_add_capability(caps, &captgt.header, sizeof(captgt));
+	if (ret)
+		return ret;
+
+	return vfio_info_add_capability(caps, &capspd.header, sizeof(capspd));
+}
+
+static const struct vfio_pci_regops vfio_pci_npu2_regops = {
+	.rw = vfio_pci_npu2_rw,
+	.mmap = vfio_pci_npu2_mmap,
+	.release = vfio_pci_npu2_release,
+	.add_capability = vfio_pci_npu2_add_capability,
+};
+
+int vfio_pci_ibm_npu2_init(struct vfio_pci_device *vdev)
+{
+	int ret;
+	struct vfio_pci_npu2_data *data;
+	struct device_node *nvlink_dn;
+	u32 nvlink_index = 0;
+	struct pci_dev *npdev = vdev->pdev;
+	struct device_node *npu_node = pci_device_to_OF_node(npdev);
+	struct pci_controller *hose = pci_bus_to_host(npdev->bus);
+	u64 mmio_atsd = 0;
+	u64 tgt = 0;
+	u32 link_speed = 0xff;
+
+	/*
+	 * PCI config space does not tell us about NVLink presense but
+	 * platform does, use this.
+	 */
+	if (!pnv_pci_get_gpu_dev(vdev->pdev))
+		return -ENODEV;
+
+	/*
+	 * NPU2 normally has 8 ATSD registers (for concurrency) and 6 links
+	 * so we can allocate one register per link, using nvlink index as
+	 * a key.
+	 * There is always at least one ATSD register so as long as at least
+	 * NVLink bridge #0 is passed to the guest, ATSD will be available.
+	 */
+	nvlink_dn = of_parse_phandle(npdev->dev.of_node, "ibm,nvlink", 0);
+	if (WARN_ON(of_property_read_u32(nvlink_dn, "ibm,npu-link-index",
+			&nvlink_index)))
+		return -ENODEV;
+
+	if (of_property_read_u64_index(hose->dn, "ibm,mmio-atsd", nvlink_index,
+			&mmio_atsd)) {
+		dev_warn(&vdev->pdev->dev, "No available ATSD found\n");
+		mmio_atsd = 0;
+	}
+
+	if (of_property_read_u64(npu_node, "ibm,device-tgt-addr", &tgt)) {
+		dev_warn(&vdev->pdev->dev, "No ibm,device-tgt-addr found\n");
+		return -EFAULT;
+	}
+
+	if (of_property_read_u32(npu_node, "ibm,nvlink-speed", &link_speed)) {
+		dev_warn(&vdev->pdev->dev, "No ibm,nvlink-speed found\n");
+		return -EFAULT;
+	}
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->mmio_atsd = mmio_atsd;
+	data->gpu_tgt = tgt;
+	data->link_speed = link_speed;
+	if (data->mmio_atsd) {
+		data->base = memremap(data->mmio_atsd, SZ_64K, MEMREMAP_WT);
+		if (!data->base) {
+			ret = -ENOMEM;
+			goto free_exit;
+		}
+	}
+
+	/*
+	 * We want to expose the capability even if this specific NVLink
+	 * did not get its own ATSD register because capabilities
+	 * belong to VFIO regions and normally there will be ATSD register
+	 * assigned to the NVLink bridge.
+	 */
+	ret = vfio_pci_register_dev_region(vdev,
+			PCI_VENDOR_ID_IBM |
+			VFIO_REGION_TYPE_PCI_VENDOR_TYPE,
+			VFIO_REGION_SUBTYPE_IBM_NVLINK2_ATSD,
+			&vfio_pci_npu2_regops,
+			data->mmio_atsd ? PAGE_SIZE : 0,
+			VFIO_REGION_INFO_FLAG_READ |
+			VFIO_REGION_INFO_FLAG_WRITE |
+			VFIO_REGION_INFO_FLAG_MMAP,
+			data);
+	if (ret)
+		goto free_exit;
+
+	return 0;
+
+free_exit:
+	kfree(data);
+
+	return ret;
+}
diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
index 42dc1d3..d0f8e4f 100644
--- a/drivers/vfio/pci/Kconfig
+++ b/drivers/vfio/pci/Kconfig
@@ -38,3 +38,9 @@ config VFIO_PCI_IGD
 	  and LPC bridge config space.
 
 	  To enable Intel IGD assignment through vfio-pci, say Y.
+
+config VFIO_PCI_NVLINK2
+	def_bool y
+	depends on VFIO_PCI && PPC_POWERNV
+	help
+	  VFIO PCI support for P9 Witherspoon machine with NVIDIA V100 GPUs
-- 
2.17.1