Re: [PATCH v2 1/3] iommu/virtio: Add topology description to virtio-iommu config space

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Feb 28, 2020 at 06:25:36PM +0100, Jean-Philippe Brucker wrote:
> Platforms without device-tree do not currently have a method for
> describing the vIOMMU topology. Provide a topology description embedded
> into the virtio device.
> 
> Use PCI FIXUP to probe the config space early, because we need to
> discover the topology before any DMA configuration takes place, and the
> virtio driver may be loaded much later. Since we discover the topology
> description when probing the PCI hierarchy, the virtual IOMMU cannot
> manage other platform devices discovered earlier.
> 
> This solution isn't elegant nor foolproof, but is the best we can do at
> the moment and works with existing virtio-iommu implementations. It also
> enables an IOMMU for lightweight hypervisors that do not rely on
> firmware methods for booting.
> 
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> ---
>  MAINTAINERS                           |   2 +
>  drivers/iommu/Kconfig                 |  10 +
>  drivers/iommu/Makefile                |   1 +
>  drivers/iommu/virtio-iommu-topology.c | 343 ++++++++++++++++++++++++++
>  drivers/iommu/virtio-iommu.c          |   3 +
>  include/linux/virt_iommu.h            |  19 ++
>  include/uapi/linux/virtio_iommu.h     |  26 ++
>  7 files changed, 404 insertions(+)
>  create mode 100644 drivers/iommu/virtio-iommu-topology.c
>  create mode 100644 include/linux/virt_iommu.h
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index fcd79fc38928..65a03ce53096 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -17781,6 +17781,8 @@ M:	Jean-Philippe Brucker <jean-philippe@linaro.org>
>  L:	virtualization@lists.linux-foundation.org
>  S:	Maintained
>  F:	drivers/iommu/virtio-iommu.c
> +F:	drivers/iommu/virtio-iommu-topology.c
> +F:	include/linux/virt_iommu.h
>  F:	include/uapi/linux/virtio_iommu.h
>  
>  VIRTUAL BOX GUEST DEVICE DRIVER
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index c5df570ef84a..f8cb45d84bb0 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -516,4 +516,14 @@ config VIRTIO_IOMMU
>  
>  	  Say Y here if you intend to run this kernel as a guest.
>  
> +config VIRTIO_IOMMU_TOPOLOGY
> +	bool "Topology properties for the virtio-iommu"
> +	depends on VIRTIO_IOMMU
> +	default y
> +	help
> +	  Enable early probing of the virtio-iommu device, to detect the
> +	  built-in topology description.
> +
> +	  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 9f33fdb3bb05..5da24280d08c 100644
> --- a/drivers/iommu/Makefile
> +++ b/drivers/iommu/Makefile
> @@ -37,3 +37,4 @@ obj-$(CONFIG_S390_IOMMU) += s390-iommu.o
>  obj-$(CONFIG_QCOM_IOMMU) += qcom_iommu.o
>  obj-$(CONFIG_HYPERV_IOMMU) += hyperv-iommu.o
>  obj-$(CONFIG_VIRTIO_IOMMU) += virtio-iommu.o
> +obj-$(CONFIG_VIRTIO_IOMMU_TOPOLOGY) += virtio-iommu-topology.o
> diff --git a/drivers/iommu/virtio-iommu-topology.c b/drivers/iommu/virtio-iommu-topology.c
> new file mode 100644
> index 000000000000..2188624ef216
> --- /dev/null
> +++ b/drivers/iommu/virtio-iommu-topology.c
> @@ -0,0 +1,343 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/dma-iommu.h>
> +#include <linux/list.h>
> +#include <linux/pci.h>
> +#include <linux/virt_iommu.h>
> +#include <linux/virtio_ids.h>
> +#include <linux/virtio_pci.h>
> +#include <uapi/linux/virtio_iommu.h>
> +
> +struct viommu_cap_config {
> +	u8 bar;
> +	u32 length; /* structure size */
> +	u32 offset; /* structure offset within the bar */
> +};
> +
> +union viommu_topo_cfg {
> +	__le16					type;
> +	struct virtio_iommu_topo_pci_range	pci;
> +	struct virtio_iommu_topo_endpoint	ep;
> +};
> +
> +struct viommu_spec {
> +	struct device				*dev; /* transport device */
> +	struct fwnode_handle			*fwnode;
> +	struct iommu_ops			*ops;
> +	struct list_head			list;
> +	size_t					num_items;
> +	/* The config array of length num_items follows */
> +	union viommu_topo_cfg			cfg[];
> +};
> +
> +static LIST_HEAD(viommus);
> +static DEFINE_MUTEX(viommus_lock);
> +
> +#define VPCI_FIELD(field) offsetof(struct virtio_pci_cap, field)
> +
> +static inline int viommu_pci_find_capability(struct pci_dev *dev, u8 cfg_type,
> +					     struct viommu_cap_config *cap)
> +{
> +	int pos;
> +	u8 bar;
> +
> +	for (pos = pci_find_capability(dev, PCI_CAP_ID_VNDR);
> +	     pos > 0;
> +	     pos = pci_find_next_capability(dev, pos, PCI_CAP_ID_VNDR)) {
> +		u8 type;
> +
> +		pci_read_config_byte(dev, pos + VPCI_FIELD(cfg_type), &type);
> +		if (type != cfg_type)
> +			continue;
> +
> +		pci_read_config_byte(dev, pos + VPCI_FIELD(bar), &bar);
> +
> +		/* Ignore structures with reserved BAR values */
> +		if (type != VIRTIO_PCI_CAP_PCI_CFG && bar > 0x5)
> +			continue;
> +
> +		cap->bar = bar;
> +		pci_read_config_dword(dev, pos + VPCI_FIELD(length),
> +				      &cap->length);
> +		pci_read_config_dword(dev, pos + VPCI_FIELD(offset),
> +				      &cap->offset);
> +
> +		return pos;
> +	}
> +	return 0;
> +}
> +
> +static void viommu_ccopy(__le32 *dst, u32 __iomem *src, size_t length)
> +{
> +	size_t i;
> +
> +	/* For the moment all our config structures align on 32b */
> +	if (WARN_ON(length % 4))
> +		return;
> +
> +	for (i = 0; i < length / 4; i++)
> +		/* Keep little-endian data */
> +		dst[i] = cpu_to_le32(ioread32(src + i));
> +}
> +
> +static int viommu_parse_topology(struct device *dev,
> +				 struct virtio_iommu_config __iomem *cfg)


why is this int? always succeeds and callers don't use the return code
...


> +{
> +	size_t i;
> +	size_t spec_length;
> +	struct viommu_spec *viommu_spec;
> +	u32 offset, item_length, num_items;
> +
> +	offset = ioread32(&cfg->topo_config.offset);
> +	item_length = ioread32(&cfg->topo_config.item_length);
> +	num_items = ioread32(&cfg->topo_config.num_items);
> +	if (!offset || !num_items || !item_length)
> +		return 0;
> +
> +	spec_length = sizeof(*viommu_spec) + num_items *
> +					     sizeof(union viommu_topo_cfg);


This can overflow. Worth detecting and failing init if it does?


> +	viommu_spec = kzalloc(spec_length, GFP_KERNEL);
> +	if (!viommu_spec)
> +		return -ENOMEM;
> +
> +	viommu_spec->dev = dev;
> +
> +	/* Copy in the whole array, sort it out later */
> +	for (i = 0; i < num_items; i++) {
> +		size_t read_length = min_t(size_t, item_length,
> +					   sizeof(union viommu_topo_cfg));
> +
> +		viommu_ccopy((__le32 *)&viommu_spec->cfg[i],

Doesn't this need __force?

> +			     (void __iomem *)cfg + offset,
> +			     read_length);

> +
> +		offset += item_length;
> +	}
> +	viommu_spec->num_items = num_items;
> +
> +	mutex_lock(&viommus_lock);
> +	list_add(&viommu_spec->list, &viommus);
> +	mutex_unlock(&viommus_lock);
> +
> +	return 0;
> +}
> +
> +static void viommu_pci_parse_topology(struct pci_dev *dev)
> +{
> +	int pos;
> +	u32 features;
> +	void __iomem *regs;
> +	struct viommu_cap_config cap = {0};
> +	struct virtio_pci_common_cfg __iomem *common_cfg;
> +
> +	/*
> +	 * The virtio infrastructure might not be loaded at this point. we need
> +	 * to access the BARs ourselves.
> +	 */
> +	pos = viommu_pci_find_capability(dev, VIRTIO_PCI_CAP_COMMON_CFG, &cap);
> +	if (!pos) {
> +		pci_warn(dev, "common capability not found\n");
> +		return;
> +	}
> +
> +	if (pci_enable_device_mem(dev))
> +		return;
> +
> +	regs = pci_iomap(dev, cap.bar, 0);
> +	if (!regs)
> +		return;
> +
> +	common_cfg = regs + cap.offset;
> +

So the virtio spec says this:

The driver MUST follow this sequence to initialize a device:

\begin{enumerate}


\item Reset the device.

\item Set the ACKNOWLEDGE status bit: the guest OS has noticed the device.

\item Set the DRIVER status bit: the guest OS knows how to drive the device.

Let's follow this unless there's a good reason not to.
And I guess let's reset at the end?


> +	/* Find out if the device supports topology description */
> +	writel(0, &common_cfg->device_feature_select);
> +	features = ioread32(&common_cfg->device_feature);
> +
> +	pci_iounmap(dev, regs);
> +
> +	if (!(features & BIT(VIRTIO_IOMMU_F_TOPOLOGY))) {
> +		pci_dbg(dev, "device doesn't have topology description");
> +		return;
> +	}
> +
> +	pos = viommu_pci_find_capability(dev, VIRTIO_PCI_CAP_DEVICE_CFG, &cap);
> +	if (!pos) {
> +		pci_warn(dev, "device config capability not found\n");
> +		return;
> +	}
> +
> +	regs = pci_iomap(dev, cap.bar, 0);
> +	if (!regs)
> +		return;
> +
> +	pci_info(dev, "parsing virtio-iommu topology\n");
> +	viommu_parse_topology(&dev->dev, regs + cap.offset);
> +	pci_iounmap(dev, regs);
> +}
> +
> +/*
> + * Catch a PCI virtio-iommu implementation early to get the topology description
> + * before we start probing other endpoints.
> + */
> +DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_REDHAT_QUMRANET, 0x1040 + VIRTIO_ID_IOMMU,
> +			viommu_pci_parse_topology);
> +
> +/*
> + * Return true if the device matches this topology structure. Write the endpoint
> + * ID into epid if it's the case.
> + */
> +static bool viommu_parse_pci(struct pci_dev *pdev, union viommu_topo_cfg *cfg,
> +			     u32 *epid)
> +{
> +	u32 endpoint_start;
> +	u16 start, end, domain;
> +	u16 devid = pci_dev_id(pdev);
> +	u16 type = le16_to_cpu(cfg->type);
> +
> +	if (type != VIRTIO_IOMMU_TOPO_PCI_RANGE)
> +		return false;
> +
> +	start		= le16_to_cpu(cfg->pci.requester_start);
> +	end		= le16_to_cpu(cfg->pci.requester_end);
> +	domain		= le16_to_cpu(cfg->pci.hierarchy);
> +	endpoint_start	= le32_to_cpu(cfg->pci.endpoint_start);
> +
> +	if (pci_domain_nr(pdev->bus) == domain &&
> +	    devid >= start && devid <= end) {
> +		*epid = devid - start + endpoint_start;
> +		return true;
> +	}
> +	return false;
> +}
> +
> +static const struct iommu_ops *virt_iommu_setup(struct device *dev)
> +{
> +	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
> +	const struct iommu_ops *viommu_ops = NULL;
> +	struct fwnode_handle *viommu_fwnode;
> +	struct viommu_spec *viommu_spec;
> +	struct pci_dev *pci_dev = NULL;
> +	struct device *viommu_dev;
> +	bool found = false;
> +	size_t i;
> +	u32 epid;
> +	int ret;
> +
> +	/* Already translated? */
> +	if (fwspec && fwspec->ops)
> +		return NULL;
> +
> +	if (dev_is_pci(dev)) {
> +		pci_dev = to_pci_dev(dev);
> +	} else {
> +		/* At the moment we don't support platform devices */
> +		return NULL;
> +	}
> +
> +	mutex_lock(&viommus_lock);
> +	list_for_each_entry(viommu_spec, &viommus, list) {
> +		for (i = 0; i < viommu_spec->num_items; i++) {
> +			union viommu_topo_cfg *cfg = &viommu_spec->cfg[i];
> +
> +			found = viommu_parse_pci(pci_dev, cfg, &epid);
> +			if (found)
> +				break;
> +		}
> +		if (found) {
> +			viommu_ops = viommu_spec->ops;
> +			viommu_fwnode = viommu_spec->fwnode;
> +			viommu_dev = viommu_spec->dev;
> +			break;
> +		}
> +	}
> +	mutex_unlock(&viommus_lock);
> +	if (!found)
> +		return NULL;
> +
> +	/* We're not translating ourselves. */
> +	if (viommu_dev == dev)
> +		return NULL;
> +
> +	/*
> +	 * If we found a PCI range managed by the viommu, we're the ones that
> +	 * have to request ACS.
> +	 */
> +	if (pci_dev)
> +		pci_request_acs();
> +
> +	if (!viommu_ops)
> +		return ERR_PTR(-EPROBE_DEFER);
> +
> +	ret = iommu_fwspec_init(dev, viommu_fwnode, viommu_ops);
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	iommu_fwspec_add_ids(dev, &epid, 1);
> +
> +	return viommu_ops;
> +}
> +
> +/**
> + * virt_dma_configure - Configure DMA of virtualized devices
> + * @dev: the endpoint
> + *
> + * Setup the DMA and IOMMU ops of a virtual device, for platforms without DT or
> + * ACPI.
> + *
> + * Return: -EPROBE_DEFER if the device is managed by an IOMMU that hasn't been
> + *   probed yet, 0 otherwise
> + */
> +int virt_dma_configure(struct device *dev)
> +{
> +	const struct iommu_ops *iommu_ops;
> +
> +	iommu_ops = virt_iommu_setup(dev);
> +	if (IS_ERR_OR_NULL(iommu_ops)) {
> +		int ret = PTR_ERR(iommu_ops);
> +
> +		if (ret == -EPROBE_DEFER || ret == 0)
> +			return ret;
> +		dev_err(dev, "error %d while setting up virt IOMMU\n", ret);
> +		return 0;
> +	}
> +
> +	/*
> +	 * If we have reason to believe the IOMMU driver missed the initial
> +	 * add_device callback for dev, replay it to get things in order.
> +	 */
> +	if (dev->bus && !device_iommu_mapped(dev))
> +		iommu_probe_device(dev);
> +
> +	/* Assume coherent, as well as full 64-bit addresses. */
> +#ifdef CONFIG_ARCH_HAS_SETUP_DMA_OPS
> +	arch_setup_dma_ops(dev, 0, ~0ULL, iommu_ops, true);
> +#else
> +	iommu_setup_dma_ops(dev, 0, ~0ULL);
> +#endif
> +	return 0;
> +}
> +
> +/**
> + * virt_set_iommu_ops - Set the IOMMU ops of a virtual IOMMU device
> + * @dev: the IOMMU device (transport)
> + * @ops: the new IOMMU ops or NULL
> + *
> + * Setup the iommu_ops associated to a viommu_spec, once the driver is loaded
> + * and the device probed.
> + */
> +void virt_set_iommu_ops(struct device *dev, struct iommu_ops *ops)
> +{
> +	struct viommu_spec *viommu_spec;
> +
> +	mutex_lock(&viommus_lock);
> +	list_for_each_entry(viommu_spec, &viommus, list) {
> +		if (viommu_spec->dev == dev) {
> +			viommu_spec->ops = ops;
> +			viommu_spec->fwnode = ops ? dev->fwnode : NULL;
> +			break;
> +		}
> +	}
> +	mutex_unlock(&viommus_lock);
> +}
> +EXPORT_SYMBOL_GPL(virt_set_iommu_ops);
> diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
> index 93ff58632452..5429c12c879b 100644
> --- a/drivers/iommu/virtio-iommu.c
> +++ b/drivers/iommu/virtio-iommu.c
> @@ -21,6 +21,7 @@
>  #include <linux/virtio.h>
>  #include <linux/virtio_config.h>
>  #include <linux/virtio_ids.h>
> +#include <linux/virt_iommu.h>
>  #include <linux/wait.h>
>  
>  #include <uapi/linux/virtio_iommu.h>
> @@ -1075,6 +1076,7 @@ static int viommu_probe(struct virtio_device *vdev)
>  	if (ret)
>  		goto err_free_vqs;
>  
> +	virt_set_iommu_ops(dev->parent, &viommu_ops);
>  	iommu_device_set_ops(&viommu->iommu, &viommu_ops);
>  	iommu_device_set_fwnode(&viommu->iommu, parent_dev->fwnode);
>  
> @@ -1121,6 +1123,7 @@ static void viommu_remove(struct virtio_device *vdev)
>  {
>  	struct viommu_dev *viommu = vdev->priv;
>  
> +	virt_set_iommu_ops(vdev->dev.parent, NULL);
>  	iommu_device_sysfs_remove(&viommu->iommu);
>  	iommu_device_unregister(&viommu->iommu);
>  
> diff --git a/include/linux/virt_iommu.h b/include/linux/virt_iommu.h
> new file mode 100644
> index 000000000000..c68b03ec75ba
> --- /dev/null
> +++ b/include/linux/virt_iommu.h
> @@ -0,0 +1,19 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef VIRTIO_IOMMU_H_
> +#define VIRTIO_IOMMU_H_
> +
> +#if IS_ENABLED(CONFIG_VIRTIO_IOMMU_TOPOLOGY)
> +int virt_dma_configure(struct device *dev);
> +void virt_set_iommu_ops(struct device *dev, struct iommu_ops *ops);
> +#else /* !CONFIG_VIRTIO_IOMMU_TOPOLOGY */
> +static inline int virt_dma_configure(struct device *dev)
> +{
> +	/* Don't disturb the normal DMA configuration methods */
> +	return 0;
> +}
> +
> +static inline void virt_set_iommu_ops(struct device *dev, struct iommu_ops *ops)
> +{ }
> +#endif /* !CONFIG_VIRTIO_IOMMU_TOPOLOGY */
> +
> +#endif /* VIRTIO_IOMMU_H_ */
> diff --git a/include/uapi/linux/virtio_iommu.h b/include/uapi/linux/virtio_iommu.h
> index 237e36a280cb..ec57d215086a 100644
> --- a/include/uapi/linux/virtio_iommu.h
> +++ b/include/uapi/linux/virtio_iommu.h
> @@ -16,6 +16,7 @@
>  #define VIRTIO_IOMMU_F_BYPASS			3
>  #define VIRTIO_IOMMU_F_PROBE			4
>  #define VIRTIO_IOMMU_F_MMIO			5
> +#define VIRTIO_IOMMU_F_TOPOLOGY			6
>  
>  struct virtio_iommu_range_64 {
>  	__le64					start;
> @@ -27,6 +28,12 @@ struct virtio_iommu_range_32 {
>  	__le32					end;
>  };
>  
> +struct virtio_iommu_topo_config {
> +	__le32					offset;
> +	__le32					num_items;
> +	__le32					item_length;
> +};
> +
>  struct virtio_iommu_config {
>  	/* Supported page sizes */
>  	__le64					page_size_mask;
> @@ -36,6 +43,25 @@ struct virtio_iommu_config {
>  	struct virtio_iommu_range_32		domain_range;
>  	/* Probe buffer size */
>  	__le32					probe_size;
> +	struct virtio_iommu_topo_config		topo_config;
> +};
> +
> +#define VIRTIO_IOMMU_TOPO_PCI_RANGE		0x1
> +#define VIRTIO_IOMMU_TOPO_ENDPOINT		0x2
> +
> +struct virtio_iommu_topo_pci_range {
> +	__le16					type;
> +	__le16					hierarchy;
> +	__le16					requester_start;
> +	__le16					requester_end;
> +	__le32					endpoint_start;
> +};
> +
> +struct virtio_iommu_topo_endpoint {
> +	__le16					type;
> +	__le16					reserved;
> +	__le32					endpoint;
> +	__le64					address;
>  };
>  
>  /* Request types */
> -- 
> 2.25.0

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