Linux Virtualization - Mar 2020 - [PATCH v2 1/3] iommu/virtio: Add topology description to virtio-iommu config space

> From: Jean-Philippe Brucker
> Sent: Saturday, February 29, 2020 1:26 AM
> 
> 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
can you elaborate "isn't elegant nor foolproof" part? is there any
other
limitation (beside pci fixup) along the route, when comparing it to 
the ACPI-approach?
> 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 at redhat.com>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe at 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 at linaro.org>
>  L:	virtualization at 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)
> +{
> +	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);
> +	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],
> +			     (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;
> +
> +	/* 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
> 
> _______________________________________________
> iommu mailing list
> iommu at lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu

On Thu, Mar 05, 2020 at 08:07:32AM +0000, Tian, Kevin
wrote:
> > From: Jean-Philippe Brucker
> > Sent: Saturday, February 29, 2020 1:26 AM
> > 
> > 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
> 
> can you elaborate "isn't elegant nor foolproof" part? is
there any other
> limitation (beside pci fixup) along the route, when comparing it to 
> the ACPI-approach?
Yes "not elegant" in part because of the PCI fixup. Fixups are used to
work around bugs, and it seems strange to have one for a normal use-case.
We also have to copy some of the virtio infrastructure since this code
runs before module load. And we have to add a third DMA configuration
method.

I don't believe anymore that the "not foolproof" part is right.
After
studying the device infrastructure a little more this solution seems less
fragile than I previously thought, but it's still a big hack, and it's
only half of the story.

This patch only handles PCI-based endpoints and viommu. On ACPI platforms,
where the virtio-mmio device is specified by an object with _HID LNRO0005,
supporting virtio-iommu on MMIO requires installing a bus notifier. There
I'd rather use an ACPI table for the topology. Platforms that don't have
ACPI such as microvm specify virtio-mmio devices on the command-line.
There devices are only created when the virtio-mmio module is loaded,
which is too late. In that case I think we need to add an early pass on
the command-line, instead of a bus notifier.

Thanks,
Jean

On Wed, Mar 11, 2020 at 06:48:22PM +0100, Jean-Philippe Brucker
wrote:
> Yes "not elegant" in part because of the PCI fixup. Fixups are
used to
> work around bugs
Not really - they are for anything unusual that common PCI code can not
handle on its own.

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MST