Re: [PATCH v3 5/7] iommu: Add virtio-iommu driver

[Auger Eric <eric.auger@redhat.com>]

Hi Jean-Philippe,

On 10/12/18 6:35 PM, Michael S. Tsirkin wrote:
> On Fri, Oct 12, 2018 at 03:59:15PM +0100, Jean-Philippe Brucker wrote:
>> The virtio IOMMU is a para-virtualized device, allowing to send IOMMU
>> requests such as map/unmap over virtio transport without emulating page
>> tables. This implementation handles ATTACH, DETACH, MAP and UNMAP
>> requests.
>>
>> The bulk of the code transforms calls coming from the IOMMU API into
>> corresponding virtio requests. Mappings are kept in an interval tree
>> instead of page tables.
>>
>> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
>> ---
>>  MAINTAINERS                       |   7 +
>>  drivers/iommu/Kconfig             |  11 +
>>  drivers/iommu/Makefile            |   1 +
>>  drivers/iommu/virtio-iommu.c      | 938 ++++++++++++++++++++++++++++++
>>  include/uapi/linux/virtio_ids.h   |   1 +
>>  include/uapi/linux/virtio_iommu.h | 101 ++++
>>  6 files changed, 1059 insertions(+)
>>  create mode 100644 drivers/iommu/virtio-iommu.c
>>  create mode 100644 include/uapi/linux/virtio_iommu.h
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 48a65c3a4189..f02fa65f47e2 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -15599,6 +15599,13 @@ S:	Maintained
>>  F:	drivers/virtio/virtio_input.c
>>  F:	include/uapi/linux/virtio_input.h
>>  
>> +VIRTIO IOMMU DRIVER
>> +M:	Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
>> +L:	virtualization@lists.linux-foundation.org
>> +S:	Maintained
>> +F:	drivers/iommu/virtio-iommu.c
>> +F:	include/uapi/linux/virtio_iommu.h
>> +
>>  VIRTUAL BOX GUEST DEVICE DRIVER
>>  M:	Hans de Goede <hdegoede@redhat.com>
>>  M:	Arnd Bergmann <arnd@arndb.de>
>> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
>> index c60395b7470f..2dc016dc2b92 100644
>> --- a/drivers/iommu/Kconfig
>> +++ b/drivers/iommu/Kconfig
>> @@ -414,4 +414,15 @@ config QCOM_IOMMU
>>  	help
>>  	  Support for IOMMU on certain Qualcomm SoCs.
>>  
>> +config VIRTIO_IOMMU
>> +	bool "Virtio IOMMU driver"
>> +	depends on VIRTIO=y
>> +	select IOMMU_API
>> +	select INTERVAL_TREE
>> +	select ARM_DMA_USE_IOMMU if ARM
>> +	help
>> +	  Para-virtualised IOMMU driver with virtio.
>> +
>> +	  Say Y here if you intend to run this kernel as a guest.
>> +
>>  endif # IOMMU_SUPPORT
>> diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
>> index ab5eba6edf82..4cd643408e49 100644
>> --- a/drivers/iommu/Makefile
>> +++ b/drivers/iommu/Makefile
>> @@ -31,3 +31,4 @@ obj-$(CONFIG_EXYNOS_IOMMU) += exynos-iommu.o
>>  obj-$(CONFIG_FSL_PAMU) += fsl_pamu.o fsl_pamu_domain.o
>>  obj-$(CONFIG_S390_IOMMU) += s390-iommu.o
>>  obj-$(CONFIG_QCOM_IOMMU) += qcom_iommu.o
>> +obj-$(CONFIG_VIRTIO_IOMMU) += virtio-iommu.o
>> diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
>> new file mode 100644
>> index 000000000000..9fb38cd3b727
>> --- /dev/null
>> +++ b/drivers/iommu/virtio-iommu.c
>> @@ -0,0 +1,938 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Virtio driver for the paravirtualized IOMMU
>> + *
>> + * Copyright (C) 2018 Arm Limited
>> + */
>> +
>> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>> +
>> +#include <linux/amba/bus.h>
>> +#include <linux/delay.h>
>> +#include <linux/dma-iommu.h>
>> +#include <linux/freezer.h>
>> +#include <linux/interval_tree.h>
>> +#include <linux/iommu.h>
>> +#include <linux/module.h>
>> +#include <linux/of_iommu.h>
>> +#include <linux/of_platform.h>
>> +#include <linux/pci.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/virtio.h>
>> +#include <linux/virtio_config.h>
>> +#include <linux/virtio_ids.h>
>> +#include <linux/wait.h>
>> +
>> +#include <uapi/linux/virtio_iommu.h>
>> +
>> +#define MSI_IOVA_BASE			0x8000000
>> +#define MSI_IOVA_LENGTH			0x100000
>> +
>> +#define VIOMMU_REQUEST_VQ		0
>> +#define VIOMMU_NR_VQS			1
>> +
>> +/*
>> + * During development, it is convenient to time out rather than wait
>> + * indefinitely in atomic context when a device misbehaves and a request doesn't
>> + * return. In production however, some requests shouldn't return until they are
>> + * successful.
>> + */
>> +#ifdef DEBUG
>> +#define VIOMMU_REQUEST_TIMEOUT		10000 /* 10s */
>> +#endif
>> +
>> +struct viommu_dev {
>> +	struct iommu_device		iommu;
>> +	struct device			*dev;
>> +	struct virtio_device		*vdev;
>> +
>> +	struct ida			domain_ids;
>> +
>> +	struct virtqueue		*vqs[VIOMMU_NR_VQS];
>> +	spinlock_t			request_lock;
>> +	struct list_head		requests;
>> +
>> +	/* Device configuration */
>> +	struct iommu_domain_geometry	geometry;
>> +	u64				pgsize_bitmap;
>> +	u8				domain_bits;
>> +};
>> +
>> +struct viommu_mapping {
>> +	phys_addr_t			paddr;
>> +	struct interval_tree_node	iova;
>> +	u32				flags;
>> +};
>> +
>> +struct viommu_domain {
>> +	struct iommu_domain		domain;
>> +	struct viommu_dev		*viommu;
>> +	struct mutex			mutex;
>> +	unsigned int			id;
>> +
>> +	spinlock_t			mappings_lock;
>> +	struct rb_root_cached		mappings;
>> +
>> +	unsigned long			nr_endpoints;
>> +};
>> +
>> +struct viommu_endpoint {
>> +	struct viommu_dev		*viommu;
>> +	struct viommu_domain		*vdomain;
>> +};
>> +
>> +struct viommu_request {
>> +	struct list_head		list;
>> +	void				*writeback;
>> +	unsigned int			write_offset;
>> +	unsigned int			len;
>> +	char				buf[];
>> +};
>> +
>> +#define to_viommu_domain(domain)	\
>> +	container_of(domain, struct viommu_domain, domain)
>> +
>> +static int viommu_get_req_errno(void *buf, size_t len)
>> +{
>> +	struct virtio_iommu_req_tail *tail = buf + len - sizeof(*tail);
>> +
>> +	switch (tail->status) {
>> +	case VIRTIO_IOMMU_S_OK:
>> +		return 0;
>> +	case VIRTIO_IOMMU_S_UNSUPP:
>> +		return -ENOSYS;
>> +	case VIRTIO_IOMMU_S_INVAL:
>> +		return -EINVAL;
>> +	case VIRTIO_IOMMU_S_RANGE:
>> +		return -ERANGE;
>> +	case VIRTIO_IOMMU_S_NOENT:
>> +		return -ENOENT;
>> +	case VIRTIO_IOMMU_S_FAULT:
>> +		return -EFAULT;
>> +	case VIRTIO_IOMMU_S_IOERR:
>> +	case VIRTIO_IOMMU_S_DEVERR:
>> +	default:
>> +		return -EIO;
>> +	}
>> +}
>> +
>> +static void viommu_set_req_status(void *buf, size_t len, int status)
>> +{
>> +	struct virtio_iommu_req_tail *tail = buf + len - sizeof(*tail);
>> +
>> +	tail->status = status;
>> +}
>> +
>> +static off_t viommu_get_req_offset(struct viommu_dev *viommu,
>> +				   struct virtio_iommu_req_head *req,
>> +				   size_t len)
>> +{
>> +	size_t tail_size = sizeof(struct virtio_iommu_req_tail);
>> +
>> +	return len - tail_size;
>> +}
>> +
>> +/*
>> + * __viommu_sync_req - Complete all in-flight requests
>> + *
>> + * Wait for all added requests to complete. When this function returns, all
>> + * requests that were in-flight at the time of the call have completed.
>> + */
>> +static int __viommu_sync_req(struct viommu_dev *viommu)
>> +{
>> +	int ret = 0;
>> +	unsigned int len;
>> +	size_t write_len;
>> +	ktime_t timeout = 0;
>> +	struct viommu_request *req;
>> +	struct virtqueue *vq = viommu->vqs[VIOMMU_REQUEST_VQ];
>> +
>> +	assert_spin_locked(&viommu->request_lock);
>> +#ifdef DEBUG
>> +	timeout = ktime_add_ms(ktime_get(), VIOMMU_REQUEST_TIMEOUT);
>> +#endif
>> +	virtqueue_kick(vq);
>> +
>> +	while (!list_empty(&viommu->requests)) {
>> +		len = 0;
>> +		req = virtqueue_get_buf(vq, &len);
>> +		if (req == NULL) {
>> +			if (!timeout || ktime_before(ktime_get(), timeout))
>> +				continue;
>> +
>> +			/* After timeout, remove all requests */
>> +			req = list_first_entry(&viommu->requests,
>> +					       struct viommu_request, list);
>> +			ret = -ETIMEDOUT;
>> +		}
>> +
>> +		if (!len)
>> +			viommu_set_req_status(req->buf, req->len,
>> +					      VIRTIO_IOMMU_S_IOERR);
>> +
>> +		write_len = req->len - req->write_offset;
>> +		if (req->writeback && len >= write_len)
>> +			memcpy(req->writeback, req->buf + req->write_offset,
>> +			       write_len);
>> +
>> +		list_del(&req->list);
>> +		kfree(req);
> 
> So with DEBUG set, this will actually free memory that device still
> DMA's into. Hardly pretty. I think you want to mark device broken,
> queue the request and then wait for device to be reset.
> 
> 
>> +	}
>> +
>> +	return ret;
>> +}
>> +
>> +static int viommu_sync_req(struct viommu_dev *viommu)
>> +{
>> +	int ret;
>> +	unsigned long flags;
>> +
>> +	spin_lock_irqsave(&viommu->request_lock, flags);
>> +	ret = __viommu_sync_req(viommu);
>> +	if (ret)
>> +		dev_dbg(viommu->dev, "could not sync requests (%d)\n", ret);
>> +	spin_unlock_irqrestore(&viommu->request_lock, flags);
>> +
>> +	return ret;
>> +}
>> +
>> +/*
>> + * __viommu_add_request - Add one request to the queue
>> + * @buf: pointer to the request buffer
>> + * @len: length of the request buffer
>> + * @writeback: copy data back to the buffer when the request completes.
>> + *
>> + * Add a request to the queue. Only synchronize the queue if it's already full.
>> + * Otherwise don't kick the queue nor wait for requests to complete.
>> + *
>> + * When @writeback is true, data written by the device, including the request
>> + * status, is copied into @buf after the request completes. This is unsafe if
>> + * the caller allocates @buf on stack and drops the lock between add_req() and
>> + * sync_req().
>> + *
>> + * Return 0 if the request was successfully added to the queue.
>> + */
>> +static int __viommu_add_req(struct viommu_dev *viommu, void *buf, size_t len,
>> +			    bool writeback)
>> +{
>> +	int ret;
>> +	off_t write_offset;
>> +	struct viommu_request *req;
>> +	struct scatterlist top_sg, bottom_sg;
>> +	struct scatterlist *sg[2] = { &top_sg, &bottom_sg };
>> +	struct virtqueue *vq = viommu->vqs[VIOMMU_REQUEST_VQ];
>> +
>> +	assert_spin_locked(&viommu->request_lock);
>> +
>> +	write_offset = viommu_get_req_offset(viommu, buf, len);
>> +	if (!write_offset)
>> +		return -EINVAL;
>> +
>> +	req = kzalloc(sizeof(*req) + len, GFP_ATOMIC);
>> +	if (!req)
>> +		return -ENOMEM;
>> +
>> +	req->len = len;
>> +	if (writeback) {
>> +		req->writeback = buf + write_offset;
>> +		req->write_offset = write_offset;
>> +	}
>> +	memcpy(&req->buf, buf, write_offset);
>> +
>> +	sg_init_one(&top_sg, req->buf, write_offset);
>> +	sg_init_one(&bottom_sg, req->buf + write_offset, len - write_offset);
>> +
>> +	ret = virtqueue_add_sgs(vq, sg, 1, 1, req, GFP_ATOMIC);
>> +	if (ret == -ENOSPC) {
>> +		/* If the queue is full, sync and retry */
>> +		if (!__viommu_sync_req(viommu))
>> +			ret = virtqueue_add_sgs(vq, sg, 1, 1, req, GFP_ATOMIC);
>> +	}
>> +	if (ret)
>> +		goto err_free;
>> +
>> +	list_add_tail(&req->list, &viommu->requests);
>> +	return 0;
>> +
>> +err_free:
>> +	kfree(req);
>> +	return ret;
>> +}
>> +
>> +static int viommu_add_req(struct viommu_dev *viommu, void *buf, size_t len)
>> +{
>> +	int ret;
>> +	unsigned long flags;
>> +
>> +	spin_lock_irqsave(&viommu->request_lock, flags);
>> +	ret = __viommu_add_req(viommu, buf, len, false);
>> +	if (ret)
>> +		dev_dbg(viommu->dev, "could not add request: %d\n", ret);
>> +	spin_unlock_irqrestore(&viommu->request_lock, flags);
>> +
>> +	return ret;
>> +}
>> +
>> +/*
>> + * Send a request and wait for it to complete. Return the request status (as an
>> + * errno)
>> + */
>> +static int viommu_send_req_sync(struct viommu_dev *viommu, void *buf,
>> +				size_t len)
>> +{
>> +	int ret;
>> +	unsigned long flags;
>> +
>> +	spin_lock_irqsave(&viommu->request_lock, flags);
>> +
>> +	ret = __viommu_add_req(viommu, buf, len, true);
>> +	if (ret) {
>> +		dev_dbg(viommu->dev, "could not add request (%d)\n", ret);
>> +		goto out_unlock;
>> +	}
>> +
>> +	ret = __viommu_sync_req(viommu);
>> +	if (ret) {
>> +		dev_dbg(viommu->dev, "could not sync requests (%d)\n", ret);
>> +		/* Fall-through (get the actual request status) */
>> +	}
>> +
>> +	ret = viommu_get_req_errno(buf, len);
>> +out_unlock:
>> +	spin_unlock_irqrestore(&viommu->request_lock, flags);
>> +	return ret;
>> +}
>> +
>> +/*
>> + * viommu_add_mapping - add a mapping to the internal tree
>> + *
>> + * On success, return the new mapping. Otherwise return NULL.
>> + */
>> +static struct viommu_mapping *
>> +viommu_add_mapping(struct viommu_domain *vdomain, unsigned long iova,
>> +		   phys_addr_t paddr, size_t size, u32 flags)
>> +{
>> +	unsigned long irqflags;
>> +	struct viommu_mapping *mapping;
>> +
>> +	mapping = kzalloc(sizeof(*mapping), GFP_ATOMIC);
>> +	if (!mapping)
>> +		return NULL;
>> +
>> +	mapping->paddr		= paddr;
>> +	mapping->iova.start	= iova;
>> +	mapping->iova.last	= iova + size - 1;
>> +	mapping->flags		= flags;
>> +
>> +	spin_lock_irqsave(&vdomain->mappings_lock, irqflags);
>> +	interval_tree_insert(&mapping->iova, &vdomain->mappings);
>> +	spin_unlock_irqrestore(&vdomain->mappings_lock, irqflags);
>> +
>> +	return mapping;
>> +}
>> +
>> +/*
>> + * viommu_del_mappings - remove mappings from the internal tree
>> + *
>> + * @vdomain: the domain
>> + * @iova: start of the range
>> + * @size: size of the range. A size of 0 corresponds to the entire address
>> + *	space.
>> + *
>> + * On success, returns the number of unmapped bytes (>= size)
>> + */
>> +static size_t viommu_del_mappings(struct viommu_domain *vdomain,
>> +				  unsigned long iova, size_t size)
>> +{
>> +	size_t unmapped = 0;
>> +	unsigned long flags;
>> +	unsigned long last = iova + size - 1;
>> +	struct viommu_mapping *mapping = NULL;
>> +	struct interval_tree_node *node, *next;
>> +
>> +	spin_lock_irqsave(&vdomain->mappings_lock, flags);
>> +	next = interval_tree_iter_first(&vdomain->mappings, iova, last);
>> +	while (next) {
>> +		node = next;
>> +		mapping = container_of(node, struct viommu_mapping, iova);
>> +		next = interval_tree_iter_next(node, iova, last);
>> +
>> +		/* Trying to split a mapping? */
>> +		if (mapping->iova.start < iova)
>> +			break;
>> +
>> +		/*
>> +		 * Note that for a partial range, this will return the full
>> +		 * mapping so we avoid sending split requests to the device.
>> +		 */
>> +		unmapped += mapping->iova.last - mapping->iova.start + 1;
>> +
>> +		interval_tree_remove(node, &vdomain->mappings);
>> +		kfree(mapping);
>> +	}
>> +	spin_unlock_irqrestore(&vdomain->mappings_lock, flags);
>> +
>> +	return unmapped;
>> +}
>> +
>> +/*
>> + * viommu_replay_mappings - re-send MAP requests
>> + *
>> + * When reattaching a domain that was previously detached from all endpoints,
>> + * mappings were deleted from the device. Re-create the mappings available in
>> + * the internal tree.
>> + */
>> +static int viommu_replay_mappings(struct viommu_domain *vdomain)
>> +{
>> +	int ret;
ret needs to be initialized here. Otherwise this can lead to a crash in
viommu_add_device.

Thanks

Eric
>> +	unsigned long flags;
>> +	struct viommu_mapping *mapping;
>> +	struct interval_tree_node *node;
>> +	struct virtio_iommu_req_map map;
>> +
>> +	spin_lock_irqsave(&vdomain->mappings_lock, flags);
>> +	node = interval_tree_iter_first(&vdomain->mappings, 0, -1UL);
>> +	while (node) {
>> +		mapping = container_of(node, struct viommu_mapping, iova);
>> +		map = (struct virtio_iommu_req_map) {
>> +			.head.type	= VIRTIO_IOMMU_T_MAP,
>> +			.domain		= cpu_to_le32(vdomain->id),
>> +			.virt_start	= cpu_to_le64(mapping->iova.start),
>> +			.virt_end	= cpu_to_le64(mapping->iova.last),
>> +			.phys_start	= cpu_to_le64(mapping->paddr),
>> +			.flags		= cpu_to_le32(mapping->flags),
>> +		};
>> +
>> +		ret = viommu_send_req_sync(vdomain->viommu, &map, sizeof(map));
>> +		if (ret)
>> +			break;
>> +
>> +		node = interval_tree_iter_next(node, 0, -1UL);
>> +	}
>> +	spin_unlock_irqrestore(&vdomain->mappings_lock, flags);
>> +
>> +	return ret;
>> +}
>> +
>> +/* IOMMU API */
>> +
>> +static struct iommu_domain *viommu_domain_alloc(unsigned type)
>> +{
>> +	struct viommu_domain *vdomain;
>> +
>> +	if (type != IOMMU_DOMAIN_UNMANAGED && type != IOMMU_DOMAIN_DMA)
>> +		return NULL;
>> +
>> +	vdomain = kzalloc(sizeof(*vdomain), GFP_KERNEL);
>> +	if (!vdomain)
>> +		return NULL;
>> +
>> +	mutex_init(&vdomain->mutex);
>> +	spin_lock_init(&vdomain->mappings_lock);
>> +	vdomain->mappings = RB_ROOT_CACHED;
>> +
>> +	if (type == IOMMU_DOMAIN_DMA &&
>> +	    iommu_get_dma_cookie(&vdomain->domain)) {
>> +		kfree(vdomain);
>> +		return NULL;
>> +	}
>> +
>> +	return &vdomain->domain;
>> +}
>> +
>> +static int viommu_domain_finalise(struct viommu_dev *viommu,
>> +				  struct iommu_domain *domain)
>> +{
>> +	int ret;
>> +	struct viommu_domain *vdomain = to_viommu_domain(domain);
>> +	unsigned int max_domain = viommu->domain_bits > 31 ? ~0 :
>> +				  (1U << viommu->domain_bits) - 1;
>> +
>> +	vdomain->viommu		= viommu;
>> +
>> +	domain->pgsize_bitmap	= viommu->pgsize_bitmap;
>> +	domain->geometry	= viommu->geometry;
>> +
>> +	ret = ida_alloc_max(&viommu->domain_ids, max_domain, GFP_KERNEL);
>> +	if (ret >= 0)
>> +		vdomain->id = (unsigned int)ret;
>> +
>> +	return ret > 0 ? 0 : ret;
>> +}
>> +
>> +static void viommu_domain_free(struct iommu_domain *domain)
>> +{
>> +	struct viommu_domain *vdomain = to_viommu_domain(domain);
>> +
>> +	iommu_put_dma_cookie(domain);
>> +
>> +	/* Free all remaining mappings (size 2^64) */
>> +	viommu_del_mappings(vdomain, 0, 0);
>> +
>> +	if (vdomain->viommu)
>> +		ida_free(&vdomain->viommu->domain_ids, vdomain->id);
>> +
>> +	kfree(vdomain);
>> +}
>> +
>> +static int viommu_attach_dev(struct iommu_domain *domain, struct device *dev)
>> +{
>> +	int i;
>> +	int ret = 0;
>> +	struct virtio_iommu_req_attach req;
>> +	struct iommu_fwspec *fwspec = dev->iommu_fwspec;
>> +	struct viommu_endpoint *vdev = fwspec->iommu_priv;
>> +	struct viommu_domain *vdomain = to_viommu_domain(domain);
>> +
>> +	mutex_lock(&vdomain->mutex);
>> +	if (!vdomain->viommu) {
>> +		/*
>> +		 * Initialize the domain proper now that we know which viommu
>> +		 * owns it.
>> +		 */
>> +		ret = viommu_domain_finalise(vdev->viommu, domain);
>> +	} else if (vdomain->viommu != vdev->viommu) {
>> +		dev_err(dev, "cannot attach to foreign vIOMMU\n");
>> +		ret = -EXDEV;
>> +	}
>> +	mutex_unlock(&vdomain->mutex);
>> +
>> +	if (ret)
>> +		return ret;
>> +
>> +	/*
>> +	 * In the virtio-iommu device, when attaching the endpoint to a new
>> +	 * domain, it is detached from the old one and, if as as a result the
>> +	 * old domain isn't attached to any endpoint, all mappings are removed
>> +	 * from the old domain and it is freed.
>> +	 *
>> +	 * In the driver the old domain still exists, and its mappings will be
>> +	 * recreated if it gets reattached to an endpoint. Otherwise it will be
>> +	 * freed explicitly.
>> +	 *
>> +	 * vdev->vdomain is protected by group->mutex
>> +	 */
>> +	if (vdev->vdomain)
>> +		vdev->vdomain->nr_endpoints--;
>> +
>> +	req = (struct virtio_iommu_req_attach) {
>> +		.head.type	= VIRTIO_IOMMU_T_ATTACH,
>> +		.domain		= cpu_to_le32(vdomain->id),
>> +	};
>> +
>> +	for (i = 0; i < fwspec->num_ids; i++) {
>> +		req.endpoint = cpu_to_le32(fwspec->ids[i]);
>> +
>> +		ret = viommu_send_req_sync(vdomain->viommu, &req, sizeof(req));
>> +		if (ret)
>> +			return ret;
>> +	}
>> +
>> +	if (!vdomain->nr_endpoints) {
>> +		/*
>> +		 * This endpoint is the first to be attached to the domain.
>> +		 * Replay existing mappings (e.g. SW MSI).
>> +		 */
>> +		ret = viommu_replay_mappings(vdomain);
>> +		if (ret)
>> +			return ret;
>> +	}
>> +
>> +	vdomain->nr_endpoints++;
>> +	vdev->vdomain = vdomain;
>> +
>> +	return 0;
>> +}
>> +
>> +static int viommu_map(struct iommu_domain *domain, unsigned long iova,
>> +		      phys_addr_t paddr, size_t size, int prot)
>> +{
>> +	int ret;
>> +	int flags;
>> +	struct viommu_mapping *mapping;
>> +	struct virtio_iommu_req_map map;
>> +	struct viommu_domain *vdomain = to_viommu_domain(domain);
>> +
>> +	flags = (prot & IOMMU_READ ? VIRTIO_IOMMU_MAP_F_READ : 0) |
>> +		(prot & IOMMU_WRITE ? VIRTIO_IOMMU_MAP_F_WRITE : 0) |
>> +		(prot & IOMMU_MMIO ? VIRTIO_IOMMU_MAP_F_MMIO : 0);
>> +
>> +	mapping = viommu_add_mapping(vdomain, iova, paddr, size, flags);
>> +	if (!mapping)
>> +		return -ENOMEM;
>> +
>> +	map = (struct virtio_iommu_req_map) {
>> +		.head.type	= VIRTIO_IOMMU_T_MAP,
>> +		.domain		= cpu_to_le32(vdomain->id),
>> +		.virt_start	= cpu_to_le64(iova),
>> +		.phys_start	= cpu_to_le64(paddr),
>> +		.virt_end	= cpu_to_le64(iova + size - 1),
>> +		.flags		= cpu_to_le32(flags),
>> +	};
>> +
>> +	if (!vdomain->nr_endpoints)
>> +		return 0;
>> +
>> +	ret = viommu_send_req_sync(vdomain->viommu, &map, sizeof(map));
>> +	if (ret)
>> +		viommu_del_mappings(vdomain, iova, size);
>> +
>> +	return ret;
>> +}
>> +
>> +static size_t viommu_unmap(struct iommu_domain *domain, unsigned long iova,
>> +			   size_t size)
>> +{
>> +	int ret = 0;
>> +	size_t unmapped;
>> +	struct virtio_iommu_req_unmap unmap;
>> +	struct viommu_domain *vdomain = to_viommu_domain(domain);
>> +
>> +	unmapped = viommu_del_mappings(vdomain, iova, size);
>> +	if (unmapped < size)
>> +		return 0;
>> +
>> +	/* Device already removed all mappings after detach. */
>> +	if (!vdomain->nr_endpoints)
>> +		return unmapped;
>> +
>> +	unmap = (struct virtio_iommu_req_unmap) {
>> +		.head.type	= VIRTIO_IOMMU_T_UNMAP,
>> +		.domain		= cpu_to_le32(vdomain->id),
>> +		.virt_start	= cpu_to_le64(iova),
>> +		.virt_end	= cpu_to_le64(iova + unmapped - 1),
>> +	};
>> +
>> +	ret = viommu_add_req(vdomain->viommu, &unmap, sizeof(unmap));
>> +	return ret ? 0 : unmapped;
>> +}
>> +
>> +static phys_addr_t viommu_iova_to_phys(struct iommu_domain *domain,
>> +				       dma_addr_t iova)
>> +{
>> +	u64 paddr = 0;
>> +	unsigned long flags;
>> +	struct viommu_mapping *mapping;
>> +	struct interval_tree_node *node;
>> +	struct viommu_domain *vdomain = to_viommu_domain(domain);
>> +
>> +	spin_lock_irqsave(&vdomain->mappings_lock, flags);
>> +	node = interval_tree_iter_first(&vdomain->mappings, iova, iova);
>> +	if (node) {
>> +		mapping = container_of(node, struct viommu_mapping, iova);
>> +		paddr = mapping->paddr + (iova - mapping->iova.start);
>> +	}
>> +	spin_unlock_irqrestore(&vdomain->mappings_lock, flags);
>> +
>> +	return paddr;
>> +}
>> +
>> +static void viommu_iotlb_sync(struct iommu_domain *domain)
>> +{
>> +	struct viommu_domain *vdomain = to_viommu_domain(domain);
>> +
>> +	viommu_sync_req(vdomain->viommu);
>> +}
>> +
>> +static void viommu_get_resv_regions(struct device *dev, struct list_head *head)
>> +{
>> +	struct iommu_resv_region *region;
>> +	int prot = IOMMU_WRITE | IOMMU_NOEXEC | IOMMU_MMIO;
>> +
>> +	region = iommu_alloc_resv_region(MSI_IOVA_BASE, MSI_IOVA_LENGTH, prot,
>> +					 IOMMU_RESV_SW_MSI);
>> +	if (!region)
>> +		return;
>> +
>> +	list_add_tail(&region->list, head);
>> +	iommu_dma_get_resv_regions(dev, head);
>> +}
>> +
>> +static void viommu_put_resv_regions(struct device *dev, struct list_head *head)
>> +{
>> +	struct iommu_resv_region *entry, *next;
>> +
>> +	list_for_each_entry_safe(entry, next, head, list)
>> +		kfree(entry);
>> +}
>> +
>> +static struct iommu_ops viommu_ops;
>> +static struct virtio_driver virtio_iommu_drv;
>> +
>> +static int viommu_match_node(struct device *dev, void *data)
>> +{
>> +	return dev->parent->fwnode == data;
>> +}
>> +
>> +static struct viommu_dev *viommu_get_by_fwnode(struct fwnode_handle *fwnode)
>> +{
>> +	struct device *dev = driver_find_device(&virtio_iommu_drv.driver, NULL,
>> +						fwnode, viommu_match_node);
>> +	put_device(dev);
>> +
>> +	return dev ? dev_to_virtio(dev)->priv : NULL;
>> +}
>> +
>> +static int viommu_add_device(struct device *dev)
>> +{
>> +	int ret;
>> +	struct iommu_group *group;
>> +	struct viommu_endpoint *vdev;
>> +	struct viommu_dev *viommu = NULL;
>> +	struct iommu_fwspec *fwspec = dev->iommu_fwspec;
>> +
>> +	if (!fwspec || fwspec->ops != &viommu_ops)
>> +		return -ENODEV;
>> +
>> +	viommu = viommu_get_by_fwnode(fwspec->iommu_fwnode);
>> +	if (!viommu)
>> +		return -ENODEV;
>> +
>> +	vdev = kzalloc(sizeof(*vdev), GFP_KERNEL);
>> +	if (!vdev)
>> +		return -ENOMEM;
>> +
>> +	vdev->viommu = viommu;
>> +	fwspec->iommu_priv = vdev;
>> +
>> +	ret = iommu_device_link(&viommu->iommu, dev);
>> +	if (ret)
>> +		goto err_free_dev;
>> +
>> +	/*
>> +	 * Last step creates a default domain and attaches to it. Everything
>> +	 * must be ready.
>> +	 */
>> +	group = iommu_group_get_for_dev(dev);
>> +	if (IS_ERR(group)) {
>> +		ret = PTR_ERR(group);
>> +		goto err_unlink_dev;
>> +	}
>> +
>> +	iommu_group_put(group);
>> +
>> +	return PTR_ERR_OR_ZERO(group);
>> +
>> +err_unlink_dev:
>> +	iommu_device_unlink(&viommu->iommu, dev);
>> +
>> +err_free_dev:
>> +	kfree(vdev);
>> +
>> +	return ret;
>> +}
>> +
>> +static void viommu_remove_device(struct device *dev)
>> +{
>> +	struct viommu_endpoint *vdev;
>> +	struct iommu_fwspec *fwspec = dev->iommu_fwspec;
>> +
>> +	if (!fwspec || fwspec->ops != &viommu_ops)
>> +		return;
>> +
>> +	vdev = fwspec->iommu_priv;
>> +
>> +	iommu_group_remove_device(dev);
>> +	iommu_device_unlink(&vdev->viommu->iommu, dev);
>> +	kfree(vdev);
>> +}
>> +
>> +static struct iommu_group *viommu_device_group(struct device *dev)
>> +{
>> +	if (dev_is_pci(dev))
>> +		return pci_device_group(dev);
>> +	else
>> +		return generic_device_group(dev);
>> +}
>> +
>> +static int viommu_of_xlate(struct device *dev, struct of_phandle_args *args)
>> +{
>> +	return iommu_fwspec_add_ids(dev, args->args, 1);
>> +}
>> +
>> +static struct iommu_ops viommu_ops = {
>> +	.domain_alloc		= viommu_domain_alloc,
>> +	.domain_free		= viommu_domain_free,
>> +	.attach_dev		= viommu_attach_dev,
>> +	.map			= viommu_map,
>> +	.unmap			= viommu_unmap,
>> +	.iova_to_phys		= viommu_iova_to_phys,
>> +	.iotlb_sync		= viommu_iotlb_sync,
>> +	.add_device		= viommu_add_device,
>> +	.remove_device		= viommu_remove_device,
>> +	.device_group		= viommu_device_group,
>> +	.get_resv_regions	= viommu_get_resv_regions,
>> +	.put_resv_regions	= viommu_put_resv_regions,
>> +	.of_xlate		= viommu_of_xlate,
>> +};
>> +
>> +static int viommu_init_vqs(struct viommu_dev *viommu)
>> +{
>> +	struct virtio_device *vdev = dev_to_virtio(viommu->dev);
>> +	const char *name = "request";
>> +	void *ret;
>> +
>> +	ret = virtio_find_single_vq(vdev, NULL, name);
>> +	if (IS_ERR(ret)) {
>> +		dev_err(viommu->dev, "cannot find VQ\n");
>> +		return PTR_ERR(ret);
>> +	}
>> +
>> +	viommu->vqs[VIOMMU_REQUEST_VQ] = ret;
>> +
>> +	return 0;
>> +}
>> +
>> +static int viommu_probe(struct virtio_device *vdev)
>> +{
>> +	struct device *parent_dev = vdev->dev.parent;
>> +	struct viommu_dev *viommu = NULL;
>> +	struct device *dev = &vdev->dev;
>> +	u64 input_start = 0;
>> +	u64 input_end = -1UL;
>> +	int ret;
>> +
>> +	if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1))
>> +		return -ENODEV;
> 
> I'm a bit confused about what will happen if this device
> happens to be behind an iommu itself.
> 
> If we can't handle that, should we clear PLATFORM_IOMMU
> e.g. like the balloon does?
> 
> 
>> +
>> +	viommu = devm_kzalloc(dev, sizeof(*viommu), GFP_KERNEL);
>> +	if (!viommu)
>> +		return -ENOMEM;
>> +
>> +	spin_lock_init(&viommu->request_lock);
>> +	ida_init(&viommu->domain_ids);
>> +	viommu->dev = dev;
>> +	viommu->vdev = vdev;
>> +	INIT_LIST_HEAD(&viommu->requests);
>> +
>> +	ret = viommu_init_vqs(viommu);
>> +	if (ret)
>> +		return ret;
>> +
>> +	virtio_cread(vdev, struct virtio_iommu_config, page_size_mask,
>> +		     &viommu->pgsize_bitmap);
>> +
>> +	if (!viommu->pgsize_bitmap) {
>> +		ret = -EINVAL;
>> +		goto err_free_vqs;
>> +	}
>> +
>> +	viommu->domain_bits = 32;
>> +
>> +	/* Optional features */
>> +	virtio_cread_feature(vdev, VIRTIO_IOMMU_F_INPUT_RANGE,
>> +			     struct virtio_iommu_config, input_range.start,
>> +			     &input_start);
>> +
>> +	virtio_cread_feature(vdev, VIRTIO_IOMMU_F_INPUT_RANGE,
>> +			     struct virtio_iommu_config, input_range.end,
>> +			     &input_end);
>> +
>> +	virtio_cread_feature(vdev, VIRTIO_IOMMU_F_DOMAIN_BITS,
>> +			     struct virtio_iommu_config, domain_bits,
>> +			     &viommu->domain_bits);
>> +
>> +	viommu->geometry = (struct iommu_domain_geometry) {
>> +		.aperture_start	= input_start,
>> +		.aperture_end	= input_end,
>> +		.force_aperture	= true,
>> +	};
>> +
>> +	viommu_ops.pgsize_bitmap = viommu->pgsize_bitmap;
>> +
>> +	virtio_device_ready(vdev);
>> +
>> +	ret = iommu_device_sysfs_add(&viommu->iommu, dev, NULL, "%s",
>> +				     virtio_bus_name(vdev));
>> +	if (ret)
>> +		goto err_free_vqs;
>> +
>> +	iommu_device_set_ops(&viommu->iommu, &viommu_ops);
>> +	iommu_device_set_fwnode(&viommu->iommu, parent_dev->fwnode);
>> +
>> +	iommu_device_register(&viommu->iommu);
>> +
>> +#ifdef CONFIG_PCI
>> +	if (pci_bus_type.iommu_ops != &viommu_ops) {
>> +		pci_request_acs();
>> +		ret = bus_set_iommu(&pci_bus_type, &viommu_ops);
>> +		if (ret)
>> +			goto err_unregister;
>> +	}
>> +#endif
>> +#ifdef CONFIG_ARM_AMBA
>> +	if (amba_bustype.iommu_ops != &viommu_ops) {
>> +		ret = bus_set_iommu(&amba_bustype, &viommu_ops);
>> +		if (ret)
>> +			goto err_unregister;
>> +	}
>> +#endif
>> +	if (platform_bus_type.iommu_ops != &viommu_ops) {
>> +		ret = bus_set_iommu(&platform_bus_type, &viommu_ops);
>> +		if (ret)
>> +			goto err_unregister;
>> +	}
>> +
>> +	vdev->priv = viommu;
>> +
>> +	dev_info(dev, "input address: %u bits\n",
>> +		 order_base_2(viommu->geometry.aperture_end));
>> +	dev_info(dev, "page mask: %#llx\n", viommu->pgsize_bitmap);
>> +
>> +	return 0;
>> +
>> +err_unregister:
>> +	iommu_device_sysfs_remove(&viommu->iommu);
>> +	iommu_device_unregister(&viommu->iommu);
>> +err_free_vqs:
>> +	vdev->config->del_vqs(vdev);
>> +
>> +	return ret;
>> +}
>> +
>> +static void viommu_remove(struct virtio_device *vdev)
>> +{
>> +	struct viommu_dev *viommu = vdev->priv;
>> +
>> +	iommu_device_sysfs_remove(&viommu->iommu);
>> +	iommu_device_unregister(&viommu->iommu);
>> +
>> +	/* Stop all virtqueues */
>> +	vdev->config->reset(vdev);
>> +	vdev->config->del_vqs(vdev);
>> +
>> +	dev_info(&vdev->dev, "device removed\n");
>> +}
>> +
>> +static void viommu_config_changed(struct virtio_device *vdev)
>> +{
>> +	dev_warn(&vdev->dev, "config changed\n");
>> +}
>> +
>> +static unsigned int features[] = {
>> +	VIRTIO_IOMMU_F_MAP_UNMAP,
>> +	VIRTIO_IOMMU_F_DOMAIN_BITS,
>> +	VIRTIO_IOMMU_F_INPUT_RANGE,
>> +};
>> +
>> +static struct virtio_device_id id_table[] = {
>> +	{ VIRTIO_ID_IOMMU, VIRTIO_DEV_ANY_ID },
>> +	{ 0 },
>> +};
>> +
>> +static struct virtio_driver virtio_iommu_drv = {
>> +	.driver.name		= KBUILD_MODNAME,
>> +	.driver.owner		= THIS_MODULE,
>> +	.id_table		= id_table,
>> +	.feature_table		= features,
>> +	.feature_table_size	= ARRAY_SIZE(features),
>> +	.probe			= viommu_probe,
>> +	.remove			= viommu_remove,
>> +	.config_changed		= viommu_config_changed,
>> +};
>> +
>> +module_virtio_driver(virtio_iommu_drv);
>> +
>> +MODULE_DESCRIPTION("Virtio IOMMU driver");
>> +MODULE_AUTHOR("Jean-Philippe Brucker <jean-philippe.brucker@arm.com>");
>> +MODULE_LICENSE("GPL v2");
>> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
>> index 6d5c3b2d4f4d..cfe47c5d9a56 100644
>> --- a/include/uapi/linux/virtio_ids.h
>> +++ b/include/uapi/linux/virtio_ids.h
>> @@ -43,5 +43,6 @@
>>  #define VIRTIO_ID_INPUT        18 /* virtio input */
>>  #define VIRTIO_ID_VSOCK        19 /* virtio vsock transport */
>>  #define VIRTIO_ID_CRYPTO       20 /* virtio crypto */
>> +#define VIRTIO_ID_IOMMU        23 /* virtio IOMMU */
>>  
>>  #endif /* _LINUX_VIRTIO_IDS_H */
>> diff --git a/include/uapi/linux/virtio_iommu.h b/include/uapi/linux/virtio_iommu.h
>> new file mode 100644
>> index 000000000000..e808fc7fbe82
>> --- /dev/null
>> +++ b/include/uapi/linux/virtio_iommu.h
>> @@ -0,0 +1,101 @@
>> +/* SPDX-License-Identifier: BSD-3-Clause */
>> +/*
>> + * Virtio-iommu definition v0.8
>> + *
>> + * Copyright (C) 2018 Arm Ltd.
>> + */
>> +#ifndef _UAPI_LINUX_VIRTIO_IOMMU_H
>> +#define _UAPI_LINUX_VIRTIO_IOMMU_H
>> +
>> +#include <linux/types.h>
>> +
>> +/* Feature bits */
>> +#define VIRTIO_IOMMU_F_INPUT_RANGE		0
>> +#define VIRTIO_IOMMU_F_DOMAIN_BITS		1
>> +#define VIRTIO_IOMMU_F_MAP_UNMAP		2
>> +#define VIRTIO_IOMMU_F_BYPASS			3
>> +
>> +struct virtio_iommu_config {
>> +	/* Supported page sizes */
>> +	__u64					page_size_mask;
>> +	/* Supported IOVA range */
>> +	struct virtio_iommu_range {
> 
> I'd rather we moved the definition outside even though gcc allows it -
> some old userspace compilers might not.
> 
>> +		__u64				start;
>> +		__u64				end;
>> +	} input_range;
>> +	/* Max domain ID size */
>> +	__u8					domain_bits;
> 
> Let's add explicit padding here as well?
> 
>> +};
>> +
>> +/* Request types */
>> +#define VIRTIO_IOMMU_T_ATTACH			0x01
>> +#define VIRTIO_IOMMU_T_DETACH			0x02
>> +#define VIRTIO_IOMMU_T_MAP			0x03
>> +#define VIRTIO_IOMMU_T_UNMAP			0x04
>> +
>> +/* Status types */
>> +#define VIRTIO_IOMMU_S_OK			0x00
>> +#define VIRTIO_IOMMU_S_IOERR			0x01
>> +#define VIRTIO_IOMMU_S_UNSUPP			0x02
>> +#define VIRTIO_IOMMU_S_DEVERR			0x03
>> +#define VIRTIO_IOMMU_S_INVAL			0x04
>> +#define VIRTIO_IOMMU_S_RANGE			0x05
>> +#define VIRTIO_IOMMU_S_NOENT			0x06
>> +#define VIRTIO_IOMMU_S_FAULT			0x07
>> +
>> +struct virtio_iommu_req_head {
>> +	__u8					type;
>> +	__u8					reserved[3];
>> +};
>> +
>> +struct virtio_iommu_req_tail {
>> +	__u8					status;
>> +	__u8					reserved[3];
>> +};
>> +
>> +struct virtio_iommu_req_attach {
>> +	struct virtio_iommu_req_head		head;
>> +	__le32					domain;
>> +	__le32					endpoint;
>> +	__u8					reserved[8];
>> +	struct virtio_iommu_req_tail		tail;
>> +};
>> +
>> +struct virtio_iommu_req_detach {
>> +	struct virtio_iommu_req_head		head;
>> +	__le32					domain;
>> +	__le32					endpoint;
>> +	__u8					reserved[8];
>> +	struct virtio_iommu_req_tail		tail;
>> +};
>> +
>> +#define VIRTIO_IOMMU_MAP_F_READ			(1 << 0)
>> +#define VIRTIO_IOMMU_MAP_F_WRITE		(1 << 1)
>> +#define VIRTIO_IOMMU_MAP_F_EXEC			(1 << 2)
>> +#define VIRTIO_IOMMU_MAP_F_MMIO			(1 << 3)
>> +
>> +#define VIRTIO_IOMMU_MAP_F_MASK			(VIRTIO_IOMMU_MAP_F_READ |	\
>> +						 VIRTIO_IOMMU_MAP_F_WRITE |	\
>> +						 VIRTIO_IOMMU_MAP_F_EXEC |	\
>> +						 VIRTIO_IOMMU_MAP_F_MMIO)
>> +
>> +struct virtio_iommu_req_map {
>> +	struct virtio_iommu_req_head		head;
>> +	__le32					domain;
>> +	__le64					virt_start;
>> +	__le64					virt_end;
>> +	__le64					phys_start;
>> +	__le32					flags;
>> +	struct virtio_iommu_req_tail		tail;
>> +};
>> +
>> +struct virtio_iommu_req_unmap {
>> +	struct virtio_iommu_req_head		head;
>> +	__le32					domain;
>> +	__le64					virt_start;
>> +	__le64					virt_end;
>> +	__u8					reserved[4];
>> +	struct virtio_iommu_req_tail		tail;
>> +};
>> +
>> +#endif
>> -- 
>> 2.19.1