drm/nouveau/svm: initial support for shared virtual memory

This uses HMM to mirror a process' CPU page tables into a channel's page
tables, and keep them synchronised so that both the CPU and GPU are able
to access the same memory at the same virtual address.

While this code also supports Volta/Turing, it's only enabled for Pascal
GPUs currently due to channel recovery being unreliable right now on the
later GPUs.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/Kbuild

@@ -30,6 +30,7 @@ nouveau-y += nouveau_vga.o
 # DRM - memory management
 nouveau-y += nouveau_bo.o
 nouveau-y += nouveau_gem.o
+nouveau-$(CONFIG_DRM_NOUVEAU_SVM) += nouveau_svm.o
 nouveau-y += nouveau_mem.o
 nouveau-y += nouveau_prime.o
 nouveau-y += nouveau_sgdma.o

drivers/gpu/drm/nouveau/Kconfig

@@ -71,3 +71,14 @@ config DRM_NOUVEAU_BACKLIGHT
 	help
 	  Say Y here if you want to control the backlight of your display
 	  (e.g. a laptop panel).
+
+config DRM_NOUVEAU_SVM
+	bool "(EXPERIMENTAL) Enable SVM (Shared Virtual Memory) support"
+	depends on ARCH_HAS_HMM
+	depends on DRM_NOUVEAU
+	depends on STAGING
+	select HMM_MIRROR
+	default n
+	help
+	  Say Y here if you want to enable experimental support for
+	  Shared Virtual Memory (SVM).

drivers/gpu/drm/nouveau/nouveau_chan.c

@@ -42,6 +42,7 @@
 #include "nouveau_fence.h"
 #include "nouveau_abi16.h"
 #include "nouveau_vmm.h"
+#include "nouveau_svm.h"
 
 MODULE_PARM_DESC(vram_pushbuf, "Create DMA push buffers in VRAM");
 int nouveau_vram_pushbuf;
@@ -95,6 +96,10 @@ nouveau_channel_del(struct nouveau_channel **pchan)
 
 		if (chan->fence)
 			nouveau_fence(chan->drm)->context_del(chan);
+
+		if (cli)
+			nouveau_svmm_part(chan->vmm->svmm, chan->inst);
+
 		nvif_object_fini(&chan->nvsw);
 		nvif_object_fini(&chan->gart);
 		nvif_object_fini(&chan->vram);
@@ -494,6 +499,10 @@ nouveau_channel_new(struct nouveau_drm *drm, struct nvif_device *device,
 		nouveau_channel_del(pchan);
 	}
 
+	ret = nouveau_svmm_join((*pchan)->vmm->svmm, (*pchan)->inst);
+	if (ret)
+		nouveau_channel_del(pchan);
+
 done:
 	cli->base.super = super;
 	return ret;

drivers/gpu/drm/nouveau/nouveau_drm.c

@@ -62,6 +62,7 @@
 #include "nouveau_usif.h"
 #include "nouveau_connector.h"
 #include "nouveau_platform.h"
+#include "nouveau_svm.h"
 
 MODULE_PARM_DESC(config, "option string to pass to driver core");
 static char *nouveau_config;
@@ -549,6 +550,7 @@ nouveau_drm_device_init(struct drm_device *dev)
 
 	nouveau_debugfs_init(drm);
 	nouveau_hwmon_init(dev);
+	nouveau_svm_init(drm);
 	nouveau_fbcon_init(dev);
 	nouveau_led_init(dev);
 
@@ -592,6 +594,7 @@ nouveau_drm_device_fini(struct drm_device *dev)
 
 	nouveau_led_fini(dev);
 	nouveau_fbcon_fini(dev);
+	nouveau_svm_fini(drm);
 	nouveau_hwmon_fini(dev);
 	nouveau_debugfs_fini(drm);
 
@@ -737,6 +740,7 @@ nouveau_do_suspend(struct drm_device *dev, bool runtime)
 	struct nouveau_drm *drm = nouveau_drm(dev);
 	int ret;
 
+	nouveau_svm_suspend(drm);
 	nouveau_led_suspend(dev);
 
 	if (dev->mode_config.num_crtc) {
@@ -813,7 +817,7 @@ nouveau_do_resume(struct drm_device *dev, bool runtime)
 	}
 
 	nouveau_led_resume(dev);
-
+	nouveau_svm_resume(drm);
 	return 0;
 }
 
@@ -1033,6 +1037,7 @@ nouveau_ioctls[] = {
 	DRM_IOCTL_DEF_DRV(NOUVEAU_GROBJ_ALLOC, nouveau_abi16_ioctl_grobj_alloc, DRM_AUTH|DRM_RENDER_ALLOW),
 	DRM_IOCTL_DEF_DRV(NOUVEAU_NOTIFIEROBJ_ALLOC, nouveau_abi16_ioctl_notifierobj_alloc, DRM_AUTH|DRM_RENDER_ALLOW),
 	DRM_IOCTL_DEF_DRV(NOUVEAU_GPUOBJ_FREE, nouveau_abi16_ioctl_gpuobj_free, DRM_AUTH|DRM_RENDER_ALLOW),
+	DRM_IOCTL_DEF_DRV(NOUVEAU_SVM_INIT, nouveau_svmm_init, DRM_AUTH|DRM_RENDER_ALLOW),
 	DRM_IOCTL_DEF_DRV(NOUVEAU_GEM_NEW, nouveau_gem_ioctl_new, DRM_AUTH|DRM_RENDER_ALLOW),
 	DRM_IOCTL_DEF_DRV(NOUVEAU_GEM_PUSHBUF, nouveau_gem_ioctl_pushbuf, DRM_AUTH|DRM_RENDER_ALLOW),
 	DRM_IOCTL_DEF_DRV(NOUVEAU_GEM_CPU_PREP, nouveau_gem_ioctl_cpu_prep, DRM_AUTH|DRM_RENDER_ALLOW),

drivers/gpu/drm/nouveau/nouveau_drv.h

@@ -210,6 +210,8 @@ struct nouveau_drm {
 	bool have_disp_power_ref;
 
 	struct dev_pm_domain vga_pm_domain;
+
+	struct nouveau_svm *svm;
 };
 
 static inline struct nouveau_drm *

drivers/gpu/drm/nouveau/nouveau_svm.c

+/*
+ * Copyright 2018 Red Hat Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+#include "nouveau_svm.h"
+#include "nouveau_drv.h"
+#include "nouveau_chan.h"
+
+#include <nvif/notify.h>
+#include <nvif/object.h>
+#include <nvif/vmm.h>
+
+#include <nvif/class.h>
+#include <nvif/clb069.h>
+#include <nvif/ifc00d.h>
+
+#include <linux/sched/mm.h>
+#include <linux/sort.h>
+#include <linux/hmm.h>
+
+struct nouveau_svm {
+	struct nouveau_drm *drm;
+	struct mutex mutex;
+	struct list_head inst;
+
+	struct nouveau_svm_fault_buffer {
+		int id;
+		struct nvif_object object;
+		u32 entries;
+		u32 getaddr;
+		u32 putaddr;
+		u32 get;
+		u32 put;
+		struct nvif_notify notify;
+
+		struct nouveau_svm_fault {
+			u64 inst;
+			u64 addr;
+			u64 time;
+			u32 engine;
+			u8  gpc;
+			u8  hub;
+			u8  access;
+			u8  client;
+			u8  fault;
+			struct nouveau_svmm *svmm;
+		} **fault;
+		int fault_nr;
+	} buffer[1];
+};
+
+#define SVM_DBG(s,f,a...) NV_DEBUG((s)->drm, "svm: "f"\n", ##a)
+#define SVM_ERR(s,f,a...) NV_WARN((s)->drm, "svm: "f"\n", ##a)
+
+struct nouveau_ivmm {
+	struct nouveau_svmm *svmm;
+	u64 inst;
+	struct list_head head;
+};
+
+static struct nouveau_ivmm *
+nouveau_ivmm_find(struct nouveau_svm *svm, u64 inst)
+{
+	struct nouveau_ivmm *ivmm;
+	list_for_each_entry(ivmm, &svm->inst, head) {
+		if (ivmm->inst == inst)
+			return ivmm;
+	}
+	return NULL;
+}
+
+struct nouveau_svmm {
+	struct nouveau_vmm *vmm;
+	struct {
+		unsigned long start;
+		unsigned long limit;
+	} unmanaged;
+
+	struct mutex mutex;
+
+	struct mm_struct *mm;
+	struct hmm_mirror mirror;
+};
+
+#define SVMM_DBG(s,f,a...)                                                     \
+	NV_DEBUG((s)->vmm->cli->drm, "svm-%p: "f"\n", (s), ##a)
+#define SVMM_ERR(s,f,a...)                                                     \
+	NV_WARN((s)->vmm->cli->drm, "svm-%p: "f"\n", (s), ##a)
+
+/* Unlink channel instance from SVMM. */
+void
+nouveau_svmm_part(struct nouveau_svmm *svmm, u64 inst)
+{
+	struct nouveau_ivmm *ivmm;
+	if (svmm) {
+		mutex_lock(&svmm->vmm->cli->drm->svm->mutex);
+		ivmm = nouveau_ivmm_find(svmm->vmm->cli->drm->svm, inst);
+		if (ivmm) {
+			list_del(&ivmm->head);
+			kfree(ivmm);
+		}
+		mutex_unlock(&svmm->vmm->cli->drm->svm->mutex);
+	}
+}
+
+/* Link channel instance to SVMM. */
+int
+nouveau_svmm_join(struct nouveau_svmm *svmm, u64 inst)
+{
+	struct nouveau_ivmm *ivmm;
+	if (svmm) {
+		if (!(ivmm = kmalloc(sizeof(*ivmm), GFP_KERNEL)))
+			return -ENOMEM;
+		ivmm->svmm = svmm;
+		ivmm->inst = inst;
+
+		mutex_lock(&svmm->vmm->cli->drm->svm->mutex);
+		list_add(&ivmm->head, &svmm->vmm->cli->drm->svm->inst);
+		mutex_unlock(&svmm->vmm->cli->drm->svm->mutex);
+	}
+	return 0;
+}
+
+/* Invalidate SVMM address-range on GPU. */
+static void
+nouveau_svmm_invalidate(struct nouveau_svmm *svmm, u64 start, u64 limit)
+{
+	if (limit > start) {
+		bool super = svmm->vmm->vmm.object.client->super;
+		svmm->vmm->vmm.object.client->super = true;
+		nvif_object_mthd(&svmm->vmm->vmm.object, NVIF_VMM_V0_PFNCLR,
+				 &(struct nvif_vmm_pfnclr_v0) {
+					.addr = start,
+					.size = limit - start,
+				 }, sizeof(struct nvif_vmm_pfnclr_v0));
+		svmm->vmm->vmm.object.client->super = super;
+	}
+}
+
+static int
+nouveau_svmm_sync_cpu_device_pagetables(struct hmm_mirror *mirror,
+					const struct hmm_update *update)
+{
+	struct nouveau_svmm *svmm = container_of(mirror, typeof(*svmm), mirror);
+	unsigned long start = update->start;
+	unsigned long limit = update->end;
+
+	if (!update->blockable)
+		return -EAGAIN;
+
+	SVMM_DBG(svmm, "invalidate %016lx-%016lx", start, limit);
+
+	mutex_lock(&svmm->mutex);
+	if (limit > svmm->unmanaged.start && start < svmm->unmanaged.limit) {
+		if (start < svmm->unmanaged.start) {
+			nouveau_svmm_invalidate(svmm, start,
+						svmm->unmanaged.limit);
+		}
+		start = svmm->unmanaged.limit;
+	}
+
+	nouveau_svmm_invalidate(svmm, start, limit);
+	mutex_unlock(&svmm->mutex);
+	return 0;
+}
+
+static void
+nouveau_svmm_release(struct hmm_mirror *mirror)
+{
+}
+
+static const struct hmm_mirror_ops
+nouveau_svmm = {
+	.sync_cpu_device_pagetables = nouveau_svmm_sync_cpu_device_pagetables,
+	.release = nouveau_svmm_release,
+};
+
+void
+nouveau_svmm_fini(struct nouveau_svmm **psvmm)
+{
+	struct nouveau_svmm *svmm = *psvmm;
+	if (svmm) {
+		hmm_mirror_unregister(&svmm->mirror);
+		kfree(*psvmm);
+		*psvmm = NULL;
+	}
+}
+
+int
+nouveau_svmm_init(struct drm_device *dev, void *data,
+		  struct drm_file *file_priv)
+{
+	struct nouveau_cli *cli = nouveau_cli(file_priv);
+	struct nouveau_svmm *svmm;
+	struct drm_nouveau_svm_init *args = data;
+	int ret;
+
+	/* Allocate tracking for SVM-enabled VMM. */
+	if (!(svmm = kzalloc(sizeof(*svmm), GFP_KERNEL)))
+		return -ENOMEM;
+	svmm->vmm = &cli->svm;
+	svmm->unmanaged.start = args->unmanaged_addr;
+	svmm->unmanaged.limit = args->unmanaged_addr + args->unmanaged_size;
+	mutex_init(&svmm->mutex);
+
+	/* Check that SVM isn't already enabled for the client. */
+	mutex_lock(&cli->mutex);
+	if (cli->svm.cli) {
+		ret = -EBUSY;
+		goto done;
+	}
+
+	/* Allocate a new GPU VMM that can support SVM (managed by the
+	 * client, with replayable faults enabled).
+	 *
+	 * All future channel/memory allocations will make use of this
+	 * VMM instead of the standard one.
+	 */
+	ret = nvif_vmm_init(&cli->mmu, cli->vmm.vmm.object.oclass, true,
+			    args->unmanaged_addr, args->unmanaged_size,
+			    &(struct gp100_vmm_v0) {
+				.fault_replay = true,
+			    }, sizeof(struct gp100_vmm_v0), &cli->svm.vmm);
+	if (ret)
+		goto done;
+
+	/* Enable HMM mirroring of CPU address-space to VMM. */
+	svmm->mm = get_task_mm(current);
+	down_write(&svmm->mm->mmap_sem);
+	svmm->mirror.ops = &nouveau_svmm;
+	ret = hmm_mirror_register(&svmm->mirror, svmm->mm);
+	if (ret == 0) {
+		cli->svm.svmm = svmm;
+		cli->svm.cli = cli;
+	}
+	up_write(&svmm->mm->mmap_sem);
+	mmput(svmm->mm);
+
+done:
+	if (ret)
+		nouveau_svmm_fini(&svmm);
+	mutex_unlock(&cli->mutex);
+	return ret;
+}
+
+static const u64
+nouveau_svm_pfn_flags[HMM_PFN_FLAG_MAX] = {
+	[HMM_PFN_VALID         ] = NVIF_VMM_PFNMAP_V0_V,
+	[HMM_PFN_WRITE         ] = NVIF_VMM_PFNMAP_V0_W,
+	[HMM_PFN_DEVICE_PRIVATE] = NVIF_VMM_PFNMAP_V0_VRAM,
+};
+
+static const u64
+nouveau_svm_pfn_values[HMM_PFN_VALUE_MAX] = {
+	[HMM_PFN_ERROR  ] = ~NVIF_VMM_PFNMAP_V0_V,
+	[HMM_PFN_NONE   ] =  NVIF_VMM_PFNMAP_V0_NONE,
+	[HMM_PFN_SPECIAL] = ~NVIF_VMM_PFNMAP_V0_V,
+};
+
+/* Issue fault replay for GPU to retry accesses that faulted previously. */
+static void
+nouveau_svm_fault_replay(struct nouveau_svm *svm)
+{
+	SVM_DBG(svm, "replay");
+	WARN_ON(nvif_object_mthd(&svm->drm->client.vmm.vmm.object,
+				 GP100_VMM_VN_FAULT_REPLAY,
+				 &(struct gp100_vmm_fault_replay_vn) {},
+				 sizeof(struct gp100_vmm_fault_replay_vn)));
+}
+
+/* Cancel a replayable fault that could not be handled.
+ *
+ * Cancelling the fault will trigger recovery to reset the engine
+ * and kill the offending channel (ie. GPU SIGSEGV).
+ */
+static void
+nouveau_svm_fault_cancel(struct nouveau_svm *svm,
+			 u64 inst, u8 hub, u8 gpc, u8 client)
+{
+	SVM_DBG(svm, "cancel %016llx %d %02x %02x", inst, hub, gpc, client);
+	WARN_ON(nvif_object_mthd(&svm->drm->client.vmm.vmm.object,
+				 GP100_VMM_VN_FAULT_CANCEL,
+				 &(struct gp100_vmm_fault_cancel_v0) {
+					.hub = hub,
+					.gpc = gpc,
+					.client = client,
+					.inst = inst,
+				 }, sizeof(struct gp100_vmm_fault_cancel_v0)));
+}
+
+static void
+nouveau_svm_fault_cancel_fault(struct nouveau_svm *svm,
+			       struct nouveau_svm_fault *fault)
+{
+	nouveau_svm_fault_cancel(svm, fault->inst,
+				      fault->hub,
+				      fault->gpc,
+				      fault->client);
+}
+
+static int
+nouveau_svm_fault_cmp(const void *a, const void *b)
+{
+	const struct nouveau_svm_fault *fa = *(struct nouveau_svm_fault **)a;
+	const struct nouveau_svm_fault *fb = *(struct nouveau_svm_fault **)b;
+	int ret;
+	if ((ret = (s64)fa->inst - fb->inst))
+		return ret;
+	if ((ret = (s64)fa->addr - fb->addr))
+		return ret;
+	/*XXX: atomic? */
+	return (fa->access == 0 || fa->access == 3) -
+	       (fb->access == 0 || fb->access == 3);
+}
+
+static void
+nouveau_svm_fault_cache(struct nouveau_svm *svm,
+			struct nouveau_svm_fault_buffer *buffer, u32 offset)
+{
+	struct nvif_object *memory = &buffer->object;
+	const u32 instlo = nvif_rd32(memory, offset + 0x00);
+	const u32 insthi = nvif_rd32(memory, offset + 0x04);
+	const u32 addrlo = nvif_rd32(memory, offset + 0x08);
+	const u32 addrhi = nvif_rd32(memory, offset + 0x0c);
+	const u32 timelo = nvif_rd32(memory, offset + 0x10);
+	const u32 timehi = nvif_rd32(memory, offset + 0x14);
+	const u32 engine = nvif_rd32(memory, offset + 0x18);
+	const u32   info = nvif_rd32(memory, offset + 0x1c);
+	const u64   inst = (u64)insthi << 32 | instlo;
+	const u8     gpc = (info & 0x1f000000) >> 24;
+	const u8     hub = (info & 0x00100000) >> 20;
+	const u8  client = (info & 0x00007f00) >> 8;
+	struct nouveau_svm_fault *fault;
+
+	//XXX: i think we're supposed to spin waiting */
+	if (WARN_ON(!(info & 0x80000000)))
+		return;
+
+	nvif_mask(memory, offset + 0x1c, 0x80000000, 0x00000000);
+
+	if (!buffer->fault[buffer->fault_nr]) {
+		fault = kmalloc(sizeof(*fault), GFP_KERNEL);
+		if (WARN_ON(!fault)) {
+			nouveau_svm_fault_cancel(svm, inst, hub, gpc, client);
+			return;
+		}
+		buffer->fault[buffer->fault_nr] = fault;
+	}
+
+	fault = buffer->fault[buffer->fault_nr++];
+	fault->inst   = inst;
+	fault->addr   = (u64)addrhi << 32 | addrlo;
+	fault->time   = (u64)timehi << 32 | timelo;
+	fault->engine = engine;
+	fault->gpc    = gpc;
+	fault->hub    = hub;
+	fault->access = (info & 0x000f0000) >> 16;
+	fault->client = client;
+	fault->fault  = (info & 0x0000001f);
+
+	SVM_DBG(svm, "fault %016llx %016llx %02x",
+		fault->inst, fault->addr, fault->access);
+}
+
+static int
+nouveau_svm_fault(struct nvif_notify *notify)
+{
+	struct nouveau_svm_fault_buffer *buffer =
+		container_of(notify, typeof(*buffer), notify);
+	struct nouveau_svm *svm =
+		container_of(buffer, typeof(*svm), buffer[buffer->id]);
+	struct nvif_object *device = &svm->drm->client.device.object;
+	struct nouveau_svmm *svmm;
+	struct {
+		struct {
+			struct nvif_ioctl_v0 i;
+			struct nvif_ioctl_mthd_v0 m;
+			struct nvif_vmm_pfnmap_v0 p;
+		} i;
+		u64 phys[16];
+	} args;
+	struct hmm_range range;
+	struct vm_area_struct *vma;
+	u64 inst, start, limit;
+	int fi, fn, pi, fill;
+	int replay = 0, ret;
+
+	/* Parse available fault buffer entries into a cache, and update
+	 * the GET pointer so HW can reuse the entries.
+	 */
+	SVM_DBG(svm, "fault handler");
+	if (buffer->get == buffer->put) {
+		buffer->put = nvif_rd32(device, buffer->putaddr);
+		buffer->get = nvif_rd32(device, buffer->getaddr);
+		if (buffer->get == buffer->put)
+			return NVIF_NOTIFY_KEEP;
+	}
+	buffer->fault_nr = 0;
+
+	SVM_DBG(svm, "get %08x put %08x", buffer->get, buffer->put);
+	while (buffer->get != buffer->put) {
+		nouveau_svm_fault_cache(svm, buffer, buffer->get * 0x20);
+		if (++buffer->get == buffer->entries)
+			buffer->get = 0;
+	}
+	nvif_wr32(device, buffer->getaddr, buffer->get);
+	SVM_DBG(svm, "%d fault(s) pending", buffer->fault_nr);
+
+	/* Sort parsed faults by instance pointer to prevent unnecessary
+	 * instance to SVMM translations, followed by address and access
+	 * type to reduce the amount of work when handling the faults.
+	 */
+	sort(buffer->fault, buffer->fault_nr, sizeof(*buffer->fault),
+	     nouveau_svm_fault_cmp, NULL);
+
+	/* Lookup SVMM structure for each unique instance pointer. */
+	mutex_lock(&svm->mutex);
+	for (fi = 0, svmm = NULL; fi < buffer->fault_nr; fi++) {
+		if (!svmm || buffer->fault[fi]->inst != inst) {
+			struct nouveau_ivmm *ivmm =
+				nouveau_ivmm_find(svm, buffer->fault[fi]->inst);
+			svmm = ivmm ? ivmm->svmm : NULL;
+			inst = buffer->fault[fi]->inst;
+			SVM_DBG(svm, "inst %016llx -> svm-%p", inst, svmm);
+		}
+		buffer->fault[fi]->svmm = svmm;
+	}
+	mutex_unlock(&svm->mutex);
+
+	/* Process list of faults. */
+	args.i.i.version = 0;
+	args.i.i.type = NVIF_IOCTL_V0_MTHD;
+	args.i.m.version = 0;
+	args.i.m.method = NVIF_VMM_V0_PFNMAP;
+	args.i.p.version = 0;
+
+	for (fi = 0; fn = fi + 1, fi < buffer->fault_nr; fi = fn) {
+		/* Cancel any faults from non-SVM channels. */
+		if (!(svmm = buffer->fault[fi]->svmm)) {
+			nouveau_svm_fault_cancel_fault(svm, buffer->fault[fi]);
+			continue;
+		}
+		SVMM_DBG(svmm, "addr %016llx", buffer->fault[fi]->addr);
+
+		/* We try and group handling of faults within a small
+		 * window into a single update.
+		 */
+		start = buffer->fault[fi]->addr;
+		limit = start + (ARRAY_SIZE(args.phys) << PAGE_SHIFT);
+		if (start < svmm->unmanaged.limit)
+			limit = min_t(u64, limit, svmm->unmanaged.start);
+		else
+		if (limit > svmm->unmanaged.start)
+			start = max_t(u64, start, svmm->unmanaged.limit);
+		SVMM_DBG(svmm, "wndw %016llx-%016llx", start, limit);
+
+		/* Intersect fault window with the CPU VMA, cancelling
+		 * the fault if the address is invalid.
+		 */
+		down_read(&svmm->mm->mmap_sem);
+		vma = find_vma_intersection(svmm->mm, start, limit);
+		if (!vma) {
+			SVMM_ERR(svmm, "wndw %016llx-%016llx", start, limit);
+			up_read(&svmm->mm->mmap_sem);
+			nouveau_svm_fault_cancel_fault(svm, buffer->fault[fi]);
+			continue;
+		}
+		start = max_t(u64, start, vma->vm_start);
+		limit = min_t(u64, limit, vma->vm_end);
+		SVMM_DBG(svmm, "wndw %016llx-%016llx", start, limit);
+
+		if (buffer->fault[fi]->addr != start) {
+			SVMM_ERR(svmm, "addr %016llx", buffer->fault[fi]->addr);
+			up_read(&svmm->mm->mmap_sem);
+			nouveau_svm_fault_cancel_fault(svm, buffer->fault[fi]);
+			continue;
+		}
+
+		/* Prepare the GPU-side update of all pages within the
+		 * fault window, determining required pages and access
+		 * permissions based on pending faults.
+		 */
+		args.i.p.page = PAGE_SHIFT;
+		args.i.p.addr = start;
+		for (fn = fi, pi = 0;;) {
+			/* Determine required permissions based on GPU fault
+			 * access flags.
+			 *XXX: atomic?
+			 */
+			if (buffer->fault[fn]->access != 0 /* READ. */ &&
+			    buffer->fault[fn]->access != 3 /* PREFETCH. */) {
+				args.phys[pi++] = NVIF_VMM_PFNMAP_V0_V |
+						  NVIF_VMM_PFNMAP_V0_W;
+			} else {
+				args.phys[pi++] = NVIF_VMM_PFNMAP_V0_V;
+			}
+			args.i.p.size = pi << PAGE_SHIFT;
+
+			/* It's okay to skip over duplicate addresses from the
+			 * same SVMM as faults are ordered by access type such
+			 * that only the first one needs to be handled.
+			 *
+			 * ie. WRITE faults appear first, thus any handling of
+			 * pending READ faults will already be satisfied.
+			 */
+			while (++fn < buffer->fault_nr &&
+			       buffer->fault[fn]->svmm == svmm &&
+			       buffer->fault[fn    ]->addr ==
+			       buffer->fault[fn - 1]->addr);
+
+			/* If the next fault is outside the window, or all GPU
+			 * faults have been dealt with, we're done here.
+			 */
+			if (fn >= buffer->fault_nr ||
+			    buffer->fault[fn]->svmm != svmm ||
+			    buffer->fault[fn]->addr >= limit)
+				break;
+
+			/* Fill in the gap between this fault and the next. */
+			fill = (buffer->fault[fn    ]->addr -
+				buffer->fault[fn - 1]->addr) >> PAGE_SHIFT;
+			while (--fill)
+				args.phys[pi++] = NVIF_VMM_PFNMAP_V0_NONE;
+		}
+
+		SVMM_DBG(svmm, "wndw %016llx-%016llx covering %d fault(s)",
+			 args.i.p.addr,
+			 args.i.p.addr + args.i.p.size, fn - fi);
+
+		/* Have HMM fault pages within the fault window to the GPU. */
+		range.vma = vma;
+		range.start = args.i.p.addr;
+		range.end = args.i.p.addr + args.i.p.size;
+		range.pfns = args.phys;
+		range.flags = nouveau_svm_pfn_flags;
+		range.values = nouveau_svm_pfn_values;
+		range.pfn_shift = NVIF_VMM_PFNMAP_V0_ADDR_SHIFT;
+again:
+		ret = hmm_vma_fault(&range, true);
+		if (ret == 0) {
+			mutex_lock(&svmm->mutex);
+			if (!hmm_vma_range_done(&range)) {
+				mutex_unlock(&svmm->mutex);
+				goto again;
+			}
+
+			svmm->vmm->vmm.object.client->super = true;
+			ret = nvif_object_ioctl(&svmm->vmm->vmm.object,
+						&args, sizeof(args.i) +
+						pi * sizeof(args.phys[0]),
+						NULL);
+			svmm->vmm->vmm.object.client->super = false;
+			mutex_unlock(&svmm->mutex);
+		}
+		up_read(&svmm->mm->mmap_sem);
+
+		/* Cancel any faults in the window whose pages didn't manage
+		 * to keep their valid bit, or stay writeable when required.
+		 *
+		 * If handling failed completely, cancel all faults.
+		 */
+		while (fi < fn) {
+			struct nouveau_svm_fault *fault = buffer->fault[fi++];
+			pi = (fault->addr - range.start) >> PAGE_SHIFT;
+			if (ret ||
+			     !(range.pfns[pi] & NVIF_VMM_PFNMAP_V0_V) ||
+			    (!(range.pfns[pi] & NVIF_VMM_PFNMAP_V0_W) &&
+			     fault->access != 0 && fault->access != 3)) {
+				nouveau_svm_fault_cancel_fault(svm, fault);
+				continue;
+			}
+			replay++;
+		}
+	}
+
+	/* Issue fault replay to the GPU. */
+	if (replay)
+		nouveau_svm_fault_replay(svm);
+	return NVIF_NOTIFY_KEEP;
+}
+
+static void
+nouveau_svm_fault_buffer_fini(struct nouveau_svm *svm, int id)
+{
+	struct nouveau_svm_fault_buffer *buffer = &svm->buffer[id];
+	nvif_notify_put(&buffer->notify);
+}
+
+static int
+nouveau_svm_fault_buffer_init(struct nouveau_svm *svm, int id)
+{
+	struct nouveau_svm_fault_buffer *buffer = &svm->buffer[id];
+	struct nvif_object *device = &svm->drm->client.device.object;
+	buffer->get = nvif_rd32(device, buffer->getaddr);
+	buffer->put = nvif_rd32(device, buffer->putaddr);
+	SVM_DBG(svm, "get %08x put %08x (init)", buffer->get, buffer->put);
+	return nvif_notify_get(&buffer->notify);
+}
+
+static void
+nouveau_svm_fault_buffer_dtor(struct nouveau_svm *svm, int id)
+{
+	struct nouveau_svm_fault_buffer *buffer = &svm->buffer[id];
+	int i;
+
+	if (buffer->fault) {
+		for (i = 0; buffer->fault[i] && i < buffer->entries; i++)
+			kfree(buffer->fault[i]);
+		kvfree(buffer->fault);
+	}
+
+	nouveau_svm_fault_buffer_fini(svm, id);
+
+	nvif_notify_fini(&buffer->notify);
+	nvif_object_fini(&buffer->object);
+}
+
+static int
+nouveau_svm_fault_buffer_ctor(struct nouveau_svm *svm, s32 oclass, int id)
+{
+	struct nouveau_svm_fault_buffer *buffer = &svm->buffer[id];
+	struct nouveau_drm *drm = svm->drm;
+	struct nvif_object *device = &drm->client.device.object;
+	struct nvif_clb069_v0 args = {};
+	int ret;
+
+	buffer->id = id;
+
+	ret = nvif_object_init(device, 0, oclass, &args, sizeof(args),
+			       &buffer->object);
+	if (ret < 0) {
+		SVM_ERR(svm, "Fault buffer allocation failed: %d", ret);
+		return ret;
+	}
+
+	nvif_object_map(&buffer->object, NULL, 0);
+	buffer->entries = args.entries;
+	buffer->getaddr = args.get;
+	buffer->putaddr = args.put;
+
+	ret = nvif_notify_init(&buffer->object, nouveau_svm_fault, true,
+			       NVB069_V0_NTFY_FAULT, NULL, 0, 0,
+			       &buffer->notify);
+	if (ret)
+		return ret;
+
+	buffer->fault = kvzalloc(sizeof(*buffer->fault) * buffer->entries, GFP_KERNEL);
+	if (!buffer->fault)
+		return -ENOMEM;
+
+	return nouveau_svm_fault_buffer_init(svm, id);
+}
+
+void
+nouveau_svm_resume(struct nouveau_drm *drm)
+{
+	struct nouveau_svm *svm = drm->svm;
+	if (svm)
+		nouveau_svm_fault_buffer_init(svm, 0);
+}
+
+void
+nouveau_svm_suspend(struct nouveau_drm *drm)
+{
+	struct nouveau_svm *svm = drm->svm;
+	if (svm)
+		nouveau_svm_fault_buffer_fini(svm, 0);
+}
+
+void
+nouveau_svm_fini(struct nouveau_drm *drm)
+{
+	struct nouveau_svm *svm = drm->svm;
+	if (svm) {
+		nouveau_svm_fault_buffer_dtor(svm, 0);
+		kfree(drm->svm);
+		drm->svm = NULL;
+	}
+}
+
+void
+nouveau_svm_init(struct nouveau_drm *drm)
+{
+	static const struct nvif_mclass buffers[] = {
+		{   VOLTA_FAULT_BUFFER_A, 0 },
+		{ MAXWELL_FAULT_BUFFER_A, 0 },
+		{}
+	};
+	struct nouveau_svm *svm;
+	int ret;
+
+	/* Disable on Volta and newer until channel recovery is fixed,
+	 * otherwise clients will have a trivial way to trash the GPU
+	 * for everyone.
+	 */
+	if (drm->client.device.info.family > NV_DEVICE_INFO_V0_PASCAL)
+		return;
+
+	if (!(drm->svm = svm = kzalloc(sizeof(*drm->svm), GFP_KERNEL)))
+		return;
+
+	drm->svm->drm = drm;
+	mutex_init(&drm->svm->mutex);
+	INIT_LIST_HEAD(&drm->svm->inst);
+
+	ret = nvif_mclass(&drm->client.device.object, buffers);
+	if (ret < 0) {
+		SVM_DBG(svm, "No supported fault buffer class");
+		nouveau_svm_fini(drm);
+		return;
+	}
+
+	ret = nouveau_svm_fault_buffer_ctor(svm, buffers[ret].oclass, 0);
+	if (ret) {
+		nouveau_svm_fini(drm);
+		return;
+	}
+
+	SVM_DBG(svm, "Initialised");
+}

drivers/gpu/drm/nouveau/nouveau_svm.h

+#ifndef __NOUVEAU_SVM_H__
+#define __NOUVEAU_SVM_H__
+#include <nvif/os.h>
+struct drm_device;
+struct drm_file;
+struct nouveau_drm;
+
+struct nouveau_svmm;
+
+#if IS_ENABLED(CONFIG_DRM_NOUVEAU_SVM)
+void nouveau_svm_init(struct nouveau_drm *);
+void nouveau_svm_fini(struct nouveau_drm *);
+void nouveau_svm_suspend(struct nouveau_drm *);
+void nouveau_svm_resume(struct nouveau_drm *);
+
+int nouveau_svmm_init(struct drm_device *, void *, struct drm_file *);
+void nouveau_svmm_fini(struct nouveau_svmm **);
+int nouveau_svmm_join(struct nouveau_svmm *, u64 inst);
+void nouveau_svmm_part(struct nouveau_svmm *, u64 inst);
+#else /* IS_ENABLED(CONFIG_DRM_NOUVEAU_SVM) */
+static inline void nouveau_svm_init(struct nouveau_drm *drm) {}
+static inline void nouveau_svm_fini(struct nouveau_drm *drm) {}
+static inline void nouveau_svm_suspend(struct nouveau_drm *drm) {}
+static inline void nouveau_svm_resume(struct nouveau_drm *drm) {}
+
+static inline int nouveau_svmm_init(struct drm_device *device, void *p,
+				    struct drm_file *file)
+{
+	return -ENOSYS;
+}
+
+static inline void nouveau_svmm_fini(struct nouveau_svmm **svmmp) {}
+
+static inline int nouveau_svmm_join(struct nouveau_svmm *svmm, u64 inst)
+{
+	return 0;
+}
+
+static inline void nouveau_svmm_part(struct nouveau_svmm *svmm, u64 inst) {}
+#endif /* IS_ENABLED(CONFIG_DRM_NOUVEAU_SVM) */
+#endif

drivers/gpu/drm/nouveau/nouveau_vmm.c

@@ -22,6 +22,7 @@
 #include "nouveau_vmm.h"
 #include "nouveau_drv.h"
 #include "nouveau_bo.h"
+#include "nouveau_svm.h"
 #include "nouveau_mem.h"
 
 void
@@ -119,6 +120,7 @@ nouveau_vma_new(struct nouveau_bo *nvbo, struct nouveau_vmm *vmm,
 void
 nouveau_vmm_fini(struct nouveau_vmm *vmm)
 {
+	nouveau_svmm_fini(&vmm->svmm);
 	nvif_vmm_fini(&vmm->vmm);
 	vmm->cli = NULL;
 }

drivers/gpu/drm/nouveau/nouveau_vmm.h

@@ -25,6 +25,7 @@ void nouveau_vma_unmap(struct nouveau_vma *);
 struct nouveau_vmm {
 	struct nouveau_cli *cli;
 	struct nvif_vmm vmm;
+	struct nouveau_svmm *svmm;
 };
 
 int nouveau_vmm_init(struct nouveau_cli *, s32 oclass, struct nouveau_vmm *);

include/uapi/drm/nouveau_drm.h

@@ -133,12 +133,20 @@ struct drm_nouveau_gem_cpu_fini {
 #define DRM_NOUVEAU_NOTIFIEROBJ_ALLOC  0x05 /* deprecated */
 #define DRM_NOUVEAU_GPUOBJ_FREE        0x06 /* deprecated */
 #define DRM_NOUVEAU_NVIF               0x07
+#define DRM_NOUVEAU_SVM_INIT           0x08
 #define DRM_NOUVEAU_GEM_NEW            0x40
 #define DRM_NOUVEAU_GEM_PUSHBUF        0x41
 #define DRM_NOUVEAU_GEM_CPU_PREP       0x42
 #define DRM_NOUVEAU_GEM_CPU_FINI       0x43
 #define DRM_NOUVEAU_GEM_INFO           0x44
 
+struct drm_nouveau_svm_init {
+	__u64 unmanaged_addr;
+	__u64 unmanaged_size;
+};
+
+#define DRM_IOCTL_NOUVEAU_SVM_INIT           DRM_IOWR(DRM_COMMAND_BASE + DRM_NOUVEAU_SVM_INIT, struct drm_nouveau_svm_init)
+
 #define DRM_IOCTL_NOUVEAU_GEM_NEW            DRM_IOWR(DRM_COMMAND_BASE + DRM_NOUVEAU_GEM_NEW, struct drm_nouveau_gem_new)
 #define DRM_IOCTL_NOUVEAU_GEM_PUSHBUF        DRM_IOWR(DRM_COMMAND_BASE + DRM_NOUVEAU_GEM_PUSHBUF, struct drm_nouveau_gem_pushbuf)
 #define DRM_IOCTL_NOUVEAU_GEM_CPU_PREP       DRM_IOW (DRM_COMMAND_BASE + DRM_NOUVEAU_GEM_CPU_PREP, struct drm_nouveau_gem_cpu_prep)