Message-ID: <20260121211806.000006aa@linux.microsoft.com>
Date: Wed, 21 Jan 2026 21:18:06 -0800
From: Jacob Pan <jacob.pan@...ux.microsoft.com>
To: Mukesh R <mrathor@...ux.microsoft.com>
Cc: linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
 linux-pci@...r.kernel.org, linux-arch@...r.kernel.org, kys@...rosoft.com,
 haiyangz@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com,
 longli@...rosoft.com, catalin.marinas@....com, will@...nel.org,
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, hpa@...or.com, joro@...tes.org,
 lpieralisi@...nel.org, kwilczynski@...nel.org, mani@...nel.org,
 robh@...nel.org, bhelgaas@...gle.com, arnd@...db.de,
 nunodasneves@...ux.microsoft.com, mhklinux@...look.com, Jacob Pan
 <jacob.pan@...ux.microsoft.com>
Subject: Re: [PATCH v0 12/15] x86/hyperv: Implement hyperv virtual iommu

Hi Mukesh,

On Mon, 19 Jan 2026 22:42:27 -0800
Mukesh R <mrathor@...ux.microsoft.com> wrote:

> From: Mukesh Rathor <mrathor@...ux.microsoft.com>
> 
> Add a new file to implement management of device domains, mapping and
> unmapping of iommu memory, and other iommu_ops to fit within the VFIO
> framework for PCI passthru on Hyper-V running Linux as root or L1VH
> parent. This also implements direct attach mechanism for PCI passthru,
> and it is also made to work within the VFIO framework.
> 
> At a high level, during boot the hypervisor creates a default identity
> domain and attaches all devices to it. This nicely maps to Linux iommu
> subsystem IOMMU_DOMAIN_IDENTITY domain. As a result, Linux does not
> need to explicitly ask Hyper-V to attach devices and do maps/unmaps
> during boot. As mentioned previously, Hyper-V supports two ways to do
> PCI passthru:
> 
>   1. Device Domain: root must create a device domain in the
> hypervisor, and do map/unmap hypercalls for mapping and unmapping
> guest RAM. All hypervisor communications use device id of type PCI for
>      identifying and referencing the device.
> 
>   2. Direct Attach: the hypervisor will simply use the guest's HW
>      page table for mappings, thus the host need not do map/unmap
>      device memory hypercalls. As such, direct attach passthru setup
>      during guest boot is extremely fast. A direct attached device
>      must be referenced via logical device id and not via the PCI
>      device id.
> 
> At present, L1VH root/parent only supports direct attaches. Also
> direct attach is default in non-L1VH cases because there are some
> significant performance issues with device domain implementation
> currently for guests with higher RAM (say more than 8GB), and that
> unfortunately cannot be addressed in the short term.
> 
> Signed-off-by: Mukesh Rathor <mrathor@...ux.microsoft.com>
> ---
>  MAINTAINERS                     |   1 +
>  arch/x86/include/asm/mshyperv.h |   7 +-
>  arch/x86/kernel/pci-dma.c       |   2 +
>  drivers/iommu/Makefile          |   2 +-
>  drivers/iommu/hyperv-iommu.c    | 876
> ++++++++++++++++++++++++++++++++ include/linux/hyperv.h          |
> 6 + 6 files changed, 890 insertions(+), 4 deletions(-)
>  create mode 100644 drivers/iommu/hyperv-iommu.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 381a0e086382..63160cee942c 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -11741,6 +11741,7 @@ F:	drivers/hid/hid-hyperv.c
>  F:	drivers/hv/
>  F:	drivers/infiniband/hw/mana/
>  F:	drivers/input/serio/hyperv-keyboard.c
> +F:	drivers/iommu/hyperv-iommu.c
Given we are also developing a guest iommu driver on hyperv, I think it
is more clear to name them accordingly. Perhaps, hyperv-iommu-root.c?

>  F:	drivers/iommu/hyperv-irq.c
>  F:	drivers/net/ethernet/microsoft/
>  F:	drivers/net/hyperv/
> diff --git a/arch/x86/include/asm/mshyperv.h
> b/arch/x86/include/asm/mshyperv.h index 97477c5a8487..e4ccdbbf1d12
> 100644 --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -189,16 +189,17 @@ static inline void hv_apic_init(void) {}
>  #endif
>  
>  #if IS_ENABLED(CONFIG_HYPERV_IOMMU)
> -static inline bool hv_pcidev_is_attached_dev(struct pci_dev *pdev)
> -{ return false; }       /* temporary */
> +bool hv_pcidev_is_attached_dev(struct pci_dev *pdev);
>  u64 hv_build_devid_oftype(struct pci_dev *pdev, enum hv_device_type
> type); +u64 hv_iommu_get_curr_partid(void);
>  #else	/* CONFIG_HYPERV_IOMMU */
>  static inline bool hv_pcidev_is_attached_dev(struct pci_dev *pdev)
>  { return false; }
> -
>  static inline u64 hv_build_devid_oftype(struct pci_dev *pdev,
>  				       enum hv_device_type type)
>  { return 0; }
> +static inline u64 hv_iommu_get_curr_partid(void)
> +{ return HV_PARTITION_ID_INVALID; }
>  
>  #endif	/* CONFIG_HYPERV_IOMMU */
>  
> diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
> index 6267363e0189..cfeee6505e17 100644
> --- a/arch/x86/kernel/pci-dma.c
> +++ b/arch/x86/kernel/pci-dma.c
> @@ -8,6 +8,7 @@
>  #include <linux/gfp.h>
>  #include <linux/pci.h>
>  #include <linux/amd-iommu.h>
> +#include <linux/hyperv.h>
>  
>  #include <asm/proto.h>
>  #include <asm/dma.h>
> @@ -105,6 +106,7 @@ void __init pci_iommu_alloc(void)
>  	gart_iommu_hole_init();
>  	amd_iommu_detect();
>  	detect_intel_iommu();
> +	hv_iommu_detect();
Will this driver be x86 only?

>  	swiotlb_init(x86_swiotlb_enable, x86_swiotlb_flags);
>  }
>  
> diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
> index 598c39558e7d..cc9774864b00 100644
> --- a/drivers/iommu/Makefile
> +++ b/drivers/iommu/Makefile
> @@ -30,7 +30,7 @@ obj-$(CONFIG_TEGRA_IOMMU_SMMU) += tegra-smmu.o
>  obj-$(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-$(CONFIG_HYPERV_IOMMU) += hyperv-irq.o
> +obj-$(CONFIG_HYPERV_IOMMU) += hyperv-irq.o hyperv-iommu.o
DMA and IRQ remapping should be separate

>  obj-$(CONFIG_VIRTIO_IOMMU) += virtio-iommu.o
>  obj-$(CONFIG_IOMMU_SVA) += iommu-sva.o
>  obj-$(CONFIG_IOMMU_IOPF) += io-pgfault.o
> diff --git a/drivers/iommu/hyperv-iommu.c
> b/drivers/iommu/hyperv-iommu.c new file mode 100644
> index 000000000000..548483fec6b1
> --- /dev/null
> +++ b/drivers/iommu/hyperv-iommu.c
> @@ -0,0 +1,876 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Hyper-V root vIOMMU driver.
> + * Copyright (C) 2026, Microsoft, Inc.
> + */
> +
> +#include <linux/module.h>
I don't think this is needed since this driver cannot be a module

> +#include <linux/pci.h>
> +#include <linux/dmar.h>
should not depend on Intel's DMAR

> +#include <linux/dma-map-ops.h>
> +#include <linux/interval_tree.h>
> +#include <linux/hyperv.h>
> +#include "dma-iommu.h"
> +#include <asm/iommu.h>
> +#include <asm/mshyperv.h>
> +
> +/* We will not claim these PCI devices, eg hypervisor needs it for
> debugger */ +static char *pci_devs_to_skip;
> +static int __init hv_iommu_setup_skip(char *str)
> +{
> +	pci_devs_to_skip = str;
> +
> +	return 0;
> +}
> +/* hv_iommu_skip=(SSSS:BB:DD.F)(SSSS:BB:DD.F) */
> +__setup("hv_iommu_skip=", hv_iommu_setup_skip);
> +
> +bool hv_no_attdev;	 /* disable direct device attach for
> passthru */ +EXPORT_SYMBOL_GPL(hv_no_attdev);
> +static int __init setup_hv_no_attdev(char *str)
> +{
> +	hv_no_attdev = true;
> +	return 0;
> +}
> +__setup("hv_no_attdev", setup_hv_no_attdev);
> +
> +/* Iommu device that we export to the world. HyperV supports max of
> one */ +static struct iommu_device hv_virt_iommu;
> +
> +struct hv_domain {
> +	struct iommu_domain iommu_dom;
> +	u32 domid_num;			      /* as opposed to
> domain_id.type */
> +	u32 num_attchd;		      /* number of currently
> attached devices */
rename to num_dev_attached?

> +	bool attached_dom;		      /* is this direct
> attached dom? */
> +	spinlock_t mappings_lock;	      /* protects
> mappings_tree */
> +	struct rb_root_cached mappings_tree;  /* iova to pa lookup
> tree */ +};
> +
> +#define to_hv_domain(d) container_of(d, struct hv_domain, iommu_dom)
> +
> +struct hv_iommu_mapping {
> +	phys_addr_t paddr;
> +	struct interval_tree_node iova;
> +	u32 flags;
> +};
> +
> +/*
> + * By default, during boot the hypervisor creates one Stage 2 (S2)
> default
> + * domain. Stage 2 means that the page table is controlled by the
> hypervisor.
> + *   S2 default: access to entire root partition memory. This for us
> easily
> + *		 maps to IOMMU_DOMAIN_IDENTITY in the iommu
> subsystem, and
> + *		 is called HV_DEVICE_DOMAIN_ID_S2_DEFAULT in the
> hypervisor.
> + *
> + * Device Management:
> + *   There are two ways to manage device attaches to domains:
> + *     1. Domain Attach: A device domain is created in the
> hypervisor, the
> + *			 device is attached to this domain, and
> then memory
> + *			 ranges are mapped in the map callbacks.
> + *     2. Direct Attach: No need to create a domain in the
> hypervisor for direct
> + *			 attached devices. A hypercall is made to
> tell the
> + *			 hypervisor to attach the device to a
> guest. There is
> + *			 no need for explicit memory mappings
> because the
> + *			 hypervisor will just use the guest HW
> page table.
> + *
> + * Since a direct attach is much faster, it is the default. This can
> be
> + * changed via hv_no_attdev.
> + *
> + * L1VH: hypervisor only supports direct attach.
> + */
> +
> +/*
> + * Create dummy domain to correspond to hypervisor prebuilt default
> identity
> + * domain (dummy because we do not make hypercall to create them).
> + */
> +static struct hv_domain hv_def_identity_dom;
> +
> +static bool hv_special_domain(struct hv_domain *hvdom)
> +{
> +	return hvdom == &hv_def_identity_dom;
> +}
> +
> +struct iommu_domain_geometry default_geometry = (struct
> iommu_domain_geometry) {
> +	.aperture_start = 0,
> +	.aperture_end = -1UL,
> +	.force_aperture = true,
> +};
> +
> +/*
> + * Since the relevant hypercalls can only fit less than 512 PFNs in
> the pfn
> + * array, report 1M max.
> + */
> +#define HV_IOMMU_PGSIZES (SZ_4K | SZ_1M)
> +
> +static u32 unique_id;	      /* unique numeric id of a new
> domain */ +
> +static void hv_iommu_detach_dev(struct iommu_domain *immdom,
> +				struct device *dev);
> +static size_t hv_iommu_unmap_pages(struct iommu_domain *immdom,
> ulong iova,
> +				   size_t pgsize, size_t pgcount,
> +				   struct iommu_iotlb_gather
> *gather); +
> +/*
> + * If the current thread is a VMM thread, return the partition id of
> the VM it
> + * is managing, else return HV_PARTITION_ID_INVALID.
> + */
> +u64 hv_iommu_get_curr_partid(void)
> +{
> +	u64 (*fn)(pid_t pid);
> +	u64 partid;
> +
> +	fn = symbol_get(mshv_pid_to_partid);
> +	if (!fn)
> +		return HV_PARTITION_ID_INVALID;
> +
> +	partid = fn(current->tgid);
> +	symbol_put(mshv_pid_to_partid);
> +
> +	return partid;
> +}
This function is not iommu specific. Maybe move it to mshv code?

> +
> +/* If this is a VMM thread, then this domain is for a guest VM */
> +static bool hv_curr_thread_is_vmm(void)
> +{
> +	return hv_iommu_get_curr_partid() != HV_PARTITION_ID_INVALID;
> +}
> +
> +static bool hv_iommu_capable(struct device *dev, enum iommu_cap cap)
> +{
> +	switch (cap) {
> +	case IOMMU_CAP_CACHE_COHERENCY:
> +		return true;
> +	default:
> +		return false;
> +	}
> +	return false;
> +}
> +
> +/*
> + * Check if given pci device is a direct attached device. Caller
> must have
> + * verified pdev is a valid pci device.
> + */
> +bool hv_pcidev_is_attached_dev(struct pci_dev *pdev)
> +{
> +	struct iommu_domain *iommu_domain;
> +	struct hv_domain *hvdom;
> +	struct device *dev = &pdev->dev;
> +
> +	iommu_domain = iommu_get_domain_for_dev(dev);
> +	if (iommu_domain) {
> +		hvdom = to_hv_domain(iommu_domain);
> +		return hvdom->attached_dom;
> +	}
> +
> +	return false;
> +}
> +EXPORT_SYMBOL_GPL(hv_pcidev_is_attached_dev);
Attached domain can change anytime, what guarantee does the caller have?

> +
> +/* Create a new device domain in the hypervisor */
> +static int hv_iommu_create_hyp_devdom(struct hv_domain *hvdom)
> +{
> +	u64 status;
> +	unsigned long flags;
> +	struct hv_input_device_domain *ddp;
> +	struct hv_input_create_device_domain *input;
nit: use consistent coding style, inverse Christmas tree.

> +
> +	local_irq_save(flags);
> +	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> +	memset(input, 0, sizeof(*input));
> +
> +	ddp = &input->device_domain;
> +	ddp->partition_id = HV_PARTITION_ID_SELF;
> +	ddp->domain_id.type = HV_DEVICE_DOMAIN_TYPE_S2;
> +	ddp->domain_id.id = hvdom->domid_num;
> +
> +	input->create_device_domain_flags.forward_progress_required
> = 1;
> +	input->create_device_domain_flags.inherit_owning_vtl = 0;
> +
> +	status = hv_do_hypercall(HVCALL_CREATE_DEVICE_DOMAIN, input,
> NULL); +
> +	local_irq_restore(flags);
> +
> +	if (!hv_result_success(status))
> +		hv_status_err(status, "\n");
> +
> +	return hv_result_to_errno(status);
> +}
> +
> +/* During boot, all devices are attached to this */
> +static struct iommu_domain *hv_iommu_domain_alloc_identity(struct
> device *dev) +{
> +	return &hv_def_identity_dom.iommu_dom;
> +}
> +
> +static struct iommu_domain *hv_iommu_domain_alloc_paging(struct
> device *dev) +{
> +	struct hv_domain *hvdom;
> +	int rc;
> +
> +	if (hv_l1vh_partition() && !hv_curr_thread_is_vmm() &&
> !hv_no_attdev) {
> +		pr_err("Hyper-V: l1vh iommu does not support host
> devices\n");
why is this an error if user input choose not to do direct attach?

> +		return NULL;
> +	}
> +
> +	hvdom = kzalloc(sizeof(struct hv_domain), GFP_KERNEL);
> +	if (hvdom == NULL)
> +		goto out;
> +
> +	spin_lock_init(&hvdom->mappings_lock);
> +	hvdom->mappings_tree = RB_ROOT_CACHED;
> +
> +	if (++unique_id == HV_DEVICE_DOMAIN_ID_S2_DEFAULT)   /* ie,
> 0 */
This is true only when unique_id wraps around, right? Then this driver
stops working?

can you use an IDR for the unique_id and free it as you detach instead
of doing this cyclic allocation?

> +		goto out_free;
> +
> +	hvdom->domid_num = unique_id;
> +	hvdom->iommu_dom.geometry = default_geometry;
> +	hvdom->iommu_dom.pgsize_bitmap = HV_IOMMU_PGSIZES;
> +
> +	/* For guests, by default we do direct attaches, so no
> domain in hyp */
> +	if (hv_curr_thread_is_vmm() && !hv_no_attdev)
> +		hvdom->attached_dom = true;
> +	else {
> +		rc = hv_iommu_create_hyp_devdom(hvdom);
> +		if (rc)
> +			goto out_free_id;
> +	}
> +
> +	return &hvdom->iommu_dom;
> +
> +out_free_id:
> +	unique_id--;
> +out_free:
> +	kfree(hvdom);
> +out:
> +	return NULL;
> +}
> +
> +static void hv_iommu_domain_free(struct iommu_domain *immdom)
> +{
> +	struct hv_domain *hvdom = to_hv_domain(immdom);
> +	unsigned long flags;
> +	u64 status;
> +	struct hv_input_delete_device_domain *input;
> +
> +	if (hv_special_domain(hvdom))
> +		return;
> +
> +	if (hvdom->num_attchd) {
> +		pr_err("Hyper-V: can't free busy iommu domain
> (%p)\n", immdom);
> +		return;
> +	}
> +
> +	if (!hv_curr_thread_is_vmm() || hv_no_attdev) {
> +		struct hv_input_device_domain *ddp;
> +
> +		local_irq_save(flags);
> +		input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> +		ddp = &input->device_domain;
> +		memset(input, 0, sizeof(*input));
> +
> +		ddp->partition_id = HV_PARTITION_ID_SELF;
> +		ddp->domain_id.type = HV_DEVICE_DOMAIN_TYPE_S2;
> +		ddp->domain_id.id = hvdom->domid_num;
> +
> +		status =
> hv_do_hypercall(HVCALL_DELETE_DEVICE_DOMAIN, input,
> +					 NULL);
> +		local_irq_restore(flags);
> +
> +		if (!hv_result_success(status))
> +			hv_status_err(status, "\n");
> +	}
you could free the domid here, no?

> +
> +	kfree(hvdom);
> +}
> +
> +/* Attach a device to a domain previously created in the hypervisor
> */ +static int hv_iommu_att_dev2dom(struct hv_domain *hvdom, struct
> pci_dev *pdev) +{
> +	unsigned long flags;
> +	u64 status;
> +	enum hv_device_type dev_type;
> +	struct hv_input_attach_device_domain *input;
> +
> +	local_irq_save(flags);
> +	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> +	memset(input, 0, sizeof(*input));
> +
> +	input->device_domain.partition_id = HV_PARTITION_ID_SELF;
> +	input->device_domain.domain_id.type =
> HV_DEVICE_DOMAIN_TYPE_S2;
> +	input->device_domain.domain_id.id = hvdom->domid_num;
> +
> +	/* NB: Upon guest shutdown, device is re-attached to the
> default domain
> +	 * without explicit detach.
> +	 */
> +	if (hv_l1vh_partition())
> +		dev_type = HV_DEVICE_TYPE_LOGICAL;
> +	else
> +		dev_type = HV_DEVICE_TYPE_PCI;
> +
> +	input->device_id.as_uint64 = hv_build_devid_oftype(pdev,
> dev_type); +
> +	status = hv_do_hypercall(HVCALL_ATTACH_DEVICE_DOMAIN, input,
> NULL);
> +	local_irq_restore(flags);
> +
> +	if (!hv_result_success(status))
> +		hv_status_err(status, "\n");
> +
> +	return hv_result_to_errno(status);
> +}
> +
> +/* Caller must have validated that dev is a valid pci dev */
> +static int hv_iommu_direct_attach_device(struct pci_dev *pdev)
> +{
> +	struct hv_input_attach_device *input;
> +	u64 status;
> +	int rc;
> +	unsigned long flags;
> +	union hv_device_id host_devid;
> +	enum hv_device_type dev_type;
> +	u64 ptid = hv_iommu_get_curr_partid();
> +
> +	if (ptid == HV_PARTITION_ID_INVALID) {
> +		pr_err("Hyper-V: Invalid partition id in direct
> attach\n");
> +		return -EINVAL;
> +	}
> +
> +	if (hv_l1vh_partition())
> +		dev_type = HV_DEVICE_TYPE_LOGICAL;
> +	else
> +		dev_type = HV_DEVICE_TYPE_PCI;
> +
> +	host_devid.as_uint64 = hv_build_devid_oftype(pdev, dev_type);
> +
> +	do {
> +		local_irq_save(flags);
> +		input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> +		memset(input, 0, sizeof(*input));
> +		input->partition_id = ptid;
> +		input->device_id = host_devid;
> +
> +		/* Hypervisor associates logical_id with this
> device, and in
> +		 * some hypercalls like retarget interrupts,
> logical_id must be
> +		 * used instead of the BDF. It is a required
> parameter.
> +		 */
> +		input->attdev_flags.logical_id = 1;
> +		input->logical_devid =
> +			   hv_build_devid_oftype(pdev,
> HV_DEVICE_TYPE_LOGICAL); +
> +		status = hv_do_hypercall(HVCALL_ATTACH_DEVICE,
> input, NULL);
> +		local_irq_restore(flags);
> +
> +		if (hv_result(status) ==
> HV_STATUS_INSUFFICIENT_MEMORY) {
> +			rc = hv_call_deposit_pages(NUMA_NO_NODE,
> ptid, 1);
> +			if (rc)
> +				break;
> +		}
> +	} while (hv_result(status) == HV_STATUS_INSUFFICIENT_MEMORY);
> +
> +	if (!hv_result_success(status))
> +		hv_status_err(status, "\n");
> +
> +	return hv_result_to_errno(status);
> +}
> +
> +/* This to attach a device to both host app (like DPDK) and a guest
> VM */
The IOMMU driver should be agnostic to the type of consumer, whether a
userspace driver or a VM. This comment is not necessary.

> +static int hv_iommu_attach_dev(struct iommu_domain *immdom,
> struct device *dev,
> +			       struct iommu_domain *old)
This does not match upstream kernel prototype, which kernel version is
this based on? I will stop here for now.

struct iommu_domain_ops {
	int (*attach_dev)(struct iommu_domain *domain, struct device
	*dev);

> +{
> +	struct pci_dev *pdev;
> +	int rc;
> +	struct hv_domain *hvdom_new = to_hv_domain(immdom);
> +	struct hv_domain *hvdom_prev = dev_iommu_priv_get(dev);
> +
> +	/* Only allow PCI devices for now */
> +	if (!dev_is_pci(dev))
> +		return -EINVAL;
> +
> +	pdev = to_pci_dev(dev);
> +
> +	/* l1vh does not support host device (eg DPDK) passthru */
> +	if (hv_l1vh_partition() && !hv_special_domain(hvdom_new) &&
> +	    !hvdom_new->attached_dom)
> +		return -EINVAL;
> +
> +	/*
> +	 * VFIO does not do explicit detach calls, hence check first
> if we need
> +	 * to detach first. Also, in case of guest shutdown, it's
> the VMM
> +	 * thread that attaches it back to the hv_def_identity_dom,
> and
> +	 * hvdom_prev will not be null then. It is null during boot.
> +	 */
> +	if (hvdom_prev)
> +		if (!hv_l1vh_partition() ||
> !hv_special_domain(hvdom_prev))
> +			hv_iommu_detach_dev(&hvdom_prev->iommu_dom,
> dev); +
> +	if (hv_l1vh_partition() && hv_special_domain(hvdom_new)) {
> +		dev_iommu_priv_set(dev, hvdom_new);  /* sets
> "private" field */
> +		return 0;
> +	}
> +
> +	if (hvdom_new->attached_dom)
> +		rc = hv_iommu_direct_attach_device(pdev);
> +	else
> +		rc = hv_iommu_att_dev2dom(hvdom_new, pdev);
> +
> +	if (rc && hvdom_prev) {
> +		int rc1;
> +
> +		if (hvdom_prev->attached_dom)
> +			rc1 = hv_iommu_direct_attach_device(pdev);
> +		else
> +			rc1 = hv_iommu_att_dev2dom(hvdom_prev, pdev);
> +
> +		if (rc1)
> +			pr_err("Hyper-V: iommu could not restore
> orig device state.. dev:%s\n",
> +			       dev_name(dev));
> +	}
> +
> +	if (rc == 0) {
> +		dev_iommu_priv_set(dev, hvdom_new);  /* sets
> "private" field */
> +		hvdom_new->num_attchd++;
> +	}
> +
> +	return rc;
> +}
> +
> +static void hv_iommu_det_dev_from_guest(struct hv_domain *hvdom,
> +					struct pci_dev *pdev)
> +{
> +	struct hv_input_detach_device *input;
> +	u64 status, log_devid;
> +	unsigned long flags;
> +
> +	log_devid = hv_build_devid_oftype(pdev,
> HV_DEVICE_TYPE_LOGICAL); +
> +	local_irq_save(flags);
> +	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> +	memset(input, 0, sizeof(*input));
> +
> +	input->partition_id = hv_iommu_get_curr_partid();
> +	input->logical_devid = log_devid;
> +	status = hv_do_hypercall(HVCALL_DETACH_DEVICE, input, NULL);
> +	local_irq_restore(flags);
> +
> +	if (!hv_result_success(status))
> +		hv_status_err(status, "\n");
> +}
> +
> +static void hv_iommu_det_dev_from_dom(struct hv_domain *hvdom,
> +				      struct pci_dev *pdev)
> +{
> +	u64 status, devid;
> +	unsigned long flags;
> +	struct hv_input_detach_device_domain *input;
> +
> +	devid = hv_build_devid_oftype(pdev, HV_DEVICE_TYPE_PCI);
> +
> +	local_irq_save(flags);
> +	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> +	memset(input, 0, sizeof(*input));
> +
> +	input->partition_id = HV_PARTITION_ID_SELF;
> +	input->device_id.as_uint64 = devid;
> +	status = hv_do_hypercall(HVCALL_DETACH_DEVICE_DOMAIN, input,
> NULL);
> +	local_irq_restore(flags);
> +
> +	if (!hv_result_success(status))
> +		hv_status_err(status, "\n");
> +}
> +
> +static void hv_iommu_detach_dev(struct iommu_domain *immdom, struct
> device *dev) +{
> +	struct pci_dev *pdev;
> +	struct hv_domain *hvdom = to_hv_domain(immdom);
> +
> +	/* See the attach function, only PCI devices for now */
> +	if (!dev_is_pci(dev))
> +		return;
> +
> +	if (hvdom->num_attchd == 0)
> +		pr_warn("Hyper-V: num_attchd is zero (%s)\n",
> dev_name(dev)); +
> +	pdev = to_pci_dev(dev);
> +
> +	if (hvdom->attached_dom) {
> +		hv_iommu_det_dev_from_guest(hvdom, pdev);
> +
> +		/* Do not reset attached_dom, hv_iommu_unmap_pages
> happens
> +		 * next.
> +		 */
> +	} else {
> +		hv_iommu_det_dev_from_dom(hvdom, pdev);
> +	}
> +
> +	hvdom->num_attchd--;
> +}
> +
> +static int hv_iommu_add_tree_mapping(struct hv_domain *hvdom,
> +				     unsigned long iova, phys_addr_t
> paddr,
> +				     size_t size, u32 flags)
> +{
> +	unsigned long irqflags;
> +	struct hv_iommu_mapping *mapping;
> +
> +	mapping = kzalloc(sizeof(*mapping), GFP_ATOMIC);
> +	if (!mapping)
> +		return -ENOMEM;
> +
> +	mapping->paddr = paddr;
> +	mapping->iova.start = iova;
> +	mapping->iova.last = iova + size - 1;
> +	mapping->flags = flags;
> +
> +	spin_lock_irqsave(&hvdom->mappings_lock, irqflags);
> +	interval_tree_insert(&mapping->iova, &hvdom->mappings_tree);
> +	spin_unlock_irqrestore(&hvdom->mappings_lock, irqflags);
> +
> +	return 0;
> +}
> +
> +static size_t hv_iommu_del_tree_mappings(struct hv_domain *hvdom,
> +					unsigned long iova, size_t
> size) +{
> +	unsigned long flags;
> +	size_t unmapped = 0;
> +	unsigned long last = iova + size - 1;
> +	struct hv_iommu_mapping *mapping = NULL;
> +	struct interval_tree_node *node, *next;
> +
> +	spin_lock_irqsave(&hvdom->mappings_lock, flags);
> +	next = interval_tree_iter_first(&hvdom->mappings_tree, iova,
> last);
> +	while (next) {
> +		node = next;
> +		mapping = container_of(node, struct
> hv_iommu_mapping, iova);
> +		next = interval_tree_iter_next(node, iova, last);
> +
> +		/* Trying to split a mapping? Not supported for now.
> */
> +		if (mapping->iova.start < iova)
> +			break;
> +
> +		unmapped += mapping->iova.last - mapping->iova.start
> + 1; +
> +		interval_tree_remove(node, &hvdom->mappings_tree);
> +		kfree(mapping);
> +	}
> +	spin_unlock_irqrestore(&hvdom->mappings_lock, flags);
> +
> +	return unmapped;
> +}
> +
> +/* Return: must return exact status from the hypercall without
> changes */ +static u64 hv_iommu_map_pgs(struct hv_domain *hvdom,
> +			    unsigned long iova, phys_addr_t paddr,
> +			    unsigned long npages, u32 map_flags)
> +{
> +	u64 status;
> +	int i;
> +	struct hv_input_map_device_gpa_pages *input;
> +	unsigned long flags, pfn = paddr >> HV_HYP_PAGE_SHIFT;
> +
> +	local_irq_save(flags);
> +	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> +	memset(input, 0, sizeof(*input));
> +
> +	input->device_domain.partition_id = HV_PARTITION_ID_SELF;
> +	input->device_domain.domain_id.type =
> HV_DEVICE_DOMAIN_TYPE_S2;
> +	input->device_domain.domain_id.id = hvdom->domid_num;
> +	input->map_flags = map_flags;
> +	input->target_device_va_base = iova;
> +
> +	pfn = paddr >> HV_HYP_PAGE_SHIFT;
> +	for (i = 0; i < npages; i++, pfn++)
> +		input->gpa_page_list[i] = pfn;
> +
> +	status = hv_do_rep_hypercall(HVCALL_MAP_DEVICE_GPA_PAGES,
> npages, 0,
> +				     input, NULL);
> +
> +	local_irq_restore(flags);
> +	return status;
> +}
> +
> +/*
> + * The core VFIO code loops over memory ranges calling this function
> with
> + * the largest size from HV_IOMMU_PGSIZES. cond_resched() is in
> vfio_iommu_map.
> + */
> +static int hv_iommu_map_pages(struct iommu_domain *immdom, ulong
> iova,
> +			      phys_addr_t paddr, size_t pgsize,
> size_t pgcount,
> +			      int prot, gfp_t gfp, size_t *mapped)
> +{
> +	u32 map_flags;
> +	int ret;
> +	u64 status;
> +	unsigned long npages, done = 0;
> +	struct hv_domain *hvdom = to_hv_domain(immdom);
> +	size_t size = pgsize * pgcount;
> +
> +	map_flags = HV_MAP_GPA_READABLE;	/* required */
> +	map_flags |= prot & IOMMU_WRITE ? HV_MAP_GPA_WRITABLE : 0;
> +
> +	ret = hv_iommu_add_tree_mapping(hvdom, iova, paddr, size,
> map_flags);
> +	if (ret)
> +		return ret;
> +
> +	if (hvdom->attached_dom) {
> +		*mapped = size;
> +		return 0;
> +	}
> +
> +	npages = size >> HV_HYP_PAGE_SHIFT;
> +	while (done < npages) {
> +		ulong completed, remain = npages - done;
> +
> +		status = hv_iommu_map_pgs(hvdom, iova, paddr, remain,
> +					  map_flags);
> +
> +		completed = hv_repcomp(status);
> +		done = done + completed;
> +		iova = iova + (completed << HV_HYP_PAGE_SHIFT);
> +		paddr = paddr + (completed << HV_HYP_PAGE_SHIFT);
> +
> +		if (hv_result(status) ==
> HV_STATUS_INSUFFICIENT_MEMORY) {
> +			ret = hv_call_deposit_pages(NUMA_NO_NODE,
> +
> hv_current_partition_id,
> +						    256);
> +			if (ret)
> +				break;
> +		}
> +		if (!hv_result_success(status))
> +			break;
> +	}
> +
> +	if (!hv_result_success(status)) {
> +		size_t done_size = done << HV_HYP_PAGE_SHIFT;
> +
> +		hv_status_err(status, "pgs:%lx/%lx iova:%lx\n",
> +			      done, npages, iova);
> +		/*
> +		 * lookup tree has all mappings [0 - size-1]. Below
> unmap will
> +		 * only remove from [0 - done], we need to remove
> second chunk
> +		 * [done+1 - size-1].
> +		 */
> +		hv_iommu_del_tree_mappings(hvdom, iova, size -
> done_size);
> +		hv_iommu_unmap_pages(immdom, iova - done_size,
> pgsize,
> +				     done, NULL);
> +		if (mapped)
> +			*mapped = 0;
> +	} else
> +		if (mapped)
> +			*mapped = size;
> +
> +	return hv_result_to_errno(status);
> +}
> +
> +static size_t hv_iommu_unmap_pages(struct iommu_domain *immdom,
> ulong iova,
> +				   size_t pgsize, size_t pgcount,
> +				   struct iommu_iotlb_gather *gather)
> +{
> +	unsigned long flags, npages;
> +	struct hv_input_unmap_device_gpa_pages *input;
> +	u64 status;
> +	struct hv_domain *hvdom = to_hv_domain(immdom);
> +	size_t unmapped, size = pgsize * pgcount;
> +
> +	unmapped = hv_iommu_del_tree_mappings(hvdom, iova, size);
> +	if (unmapped < size)
> +		pr_err("%s: could not delete all mappings
> (%lx:%lx/%lx)\n",
> +		       __func__, iova, unmapped, size);
> +
> +	if (hvdom->attached_dom)
> +		return size;
> +
> +	npages = size >> HV_HYP_PAGE_SHIFT;
> +
> +	local_irq_save(flags);
> +	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> +	memset(input, 0, sizeof(*input));
> +
> +	input->device_domain.partition_id = HV_PARTITION_ID_SELF;
> +	input->device_domain.domain_id.type =
> HV_DEVICE_DOMAIN_TYPE_S2;
> +	input->device_domain.domain_id.id = hvdom->domid_num;
> +	input->target_device_va_base = iova;
> +
> +	status = hv_do_rep_hypercall(HVCALL_UNMAP_DEVICE_GPA_PAGES,
> npages,
> +				     0, input, NULL);
> +	local_irq_restore(flags);
> +
> +	if (!hv_result_success(status))
> +		hv_status_err(status, "\n");
> +
> +	return unmapped;
> +}
> +
> +static phys_addr_t hv_iommu_iova_to_phys(struct iommu_domain *immdom,
> +					 dma_addr_t iova)
> +{
> +	u64 paddr = 0;
> +	unsigned long flags;
> +	struct hv_iommu_mapping *mapping;
> +	struct interval_tree_node *node;
> +	struct hv_domain *hvdom = to_hv_domain(immdom);
> +
> +	spin_lock_irqsave(&hvdom->mappings_lock, flags);
> +	node = interval_tree_iter_first(&hvdom->mappings_tree, iova,
> iova);
> +	if (node) {
> +		mapping = container_of(node, struct
> hv_iommu_mapping, iova);
> +		paddr = mapping->paddr + (iova -
> mapping->iova.start);
> +	}
> +	spin_unlock_irqrestore(&hvdom->mappings_lock, flags);
> +
> +	return paddr;
> +}
> +
> +/*
> + * Currently, hypervisor does not provide list of devices it is using
> + * dynamically. So use this to allow users to manually specify
> devices that
> + * should be skipped. (eg. hypervisor debugger using some network
> device).
> + */
> +static struct iommu_device *hv_iommu_probe_device(struct device *dev)
> +{
> +	if (!dev_is_pci(dev))
> +		return ERR_PTR(-ENODEV);
> +
> +	if (pci_devs_to_skip && *pci_devs_to_skip) {
> +		int rc, pos = 0;
> +		int parsed;
> +		int segment, bus, slot, func;
> +		struct pci_dev *pdev = to_pci_dev(dev);
> +
> +		do {
> +			parsed = 0;
> +
> +			rc = sscanf(pci_devs_to_skip + pos, "
> (%x:%x:%x.%x) %n",
> +				    &segment, &bus, &slot, &func,
> &parsed);
> +			if (rc)
> +				break;
> +			if (parsed <= 0)
> +				break;
> +
> +			if (pci_domain_nr(pdev->bus) == segment &&
> +			    pdev->bus->number == bus &&
> +			    PCI_SLOT(pdev->devfn) == slot &&
> +			    PCI_FUNC(pdev->devfn) == func) {
> +
> +				dev_info(dev, "skipped by Hyper-V
> IOMMU\n");
> +				return ERR_PTR(-ENODEV);
> +			}
> +			pos += parsed;
> +
> +		} while (pci_devs_to_skip[pos]);
> +	}
> +
> +	/* Device will be explicitly attached to the default domain,
> so no need
> +	 * to do dev_iommu_priv_set() here.
> +	 */
> +
> +	return &hv_virt_iommu;
> +}
> +
> +static void hv_iommu_probe_finalize(struct device *dev)
> +{
> +	struct iommu_domain *immdom = iommu_get_domain_for_dev(dev);
> +
> +	if (immdom && immdom->type == IOMMU_DOMAIN_DMA)
> +		iommu_setup_dma_ops(dev);
> +	else
> +		set_dma_ops(dev, NULL);
> +}
> +
> +static void hv_iommu_release_device(struct device *dev)
> +{
> +	struct hv_domain *hvdom = dev_iommu_priv_get(dev);
> +
> +	/* Need to detach device from device domain if necessary. */
> +	if (hvdom)
> +		hv_iommu_detach_dev(&hvdom->iommu_dom, dev);
> +
> +	dev_iommu_priv_set(dev, NULL);
> +	set_dma_ops(dev, NULL);
> +}
> +
> +static struct iommu_group *hv_iommu_device_group(struct device *dev)
> +{
> +	if (dev_is_pci(dev))
> +		return pci_device_group(dev);
> +	else
> +		return generic_device_group(dev);
> +}
> +
> +static int hv_iommu_def_domain_type(struct device *dev)
> +{
> +	/* The hypervisor always creates this by default during boot
> */
> +	return IOMMU_DOMAIN_IDENTITY;
> +}
> +
> +static struct iommu_ops hv_iommu_ops = {
> +	.capable	    = hv_iommu_capable,
> +	.domain_alloc_identity	=
> hv_iommu_domain_alloc_identity,
> +	.domain_alloc_paging	= hv_iommu_domain_alloc_paging,
> +	.probe_device	    = hv_iommu_probe_device,
> +	.probe_finalize     = hv_iommu_probe_finalize,
> +	.release_device     = hv_iommu_release_device,
> +	.def_domain_type    = hv_iommu_def_domain_type,
> +	.device_group	    = hv_iommu_device_group,
> +	.default_domain_ops = &(const struct iommu_domain_ops) {
> +		.attach_dev   = hv_iommu_attach_dev,
> +		.map_pages    = hv_iommu_map_pages,
> +		.unmap_pages  = hv_iommu_unmap_pages,
> +		.iova_to_phys = hv_iommu_iova_to_phys,
> +		.free	      = hv_iommu_domain_free,
> +	},
> +	.owner		    = THIS_MODULE,
> +};
> +
> +static void __init hv_initialize_special_domains(void)
> +{
> +	hv_def_identity_dom.iommu_dom.geometry = default_geometry;
> +	hv_def_identity_dom.domid_num =
> HV_DEVICE_DOMAIN_ID_S2_DEFAULT; /* 0 */ +}
This could be initialized statically.

> +
> +static int __init hv_iommu_init(void)
> +{
> +	int ret;
> +	struct iommu_device *iommup = &hv_virt_iommu;
> +
> +	if (!hv_is_hyperv_initialized())
> +		return -ENODEV;
> +
> +	ret = iommu_device_sysfs_add(iommup, NULL, NULL, "%s",
> "hyperv-iommu");
> +	if (ret) {
> +		pr_err("Hyper-V: iommu_device_sysfs_add failed:
> %d\n", ret);
> +		return ret;
> +	}
> +
> +	/* This must come before iommu_device_register because the
> latter calls
> +	 * into the hooks.
> +	 */
> +	hv_initialize_special_domains();
> +
> +	ret = iommu_device_register(iommup, &hv_iommu_ops, NULL);
> +	if (ret) {
> +		pr_err("Hyper-V: iommu_device_register failed:
> %d\n", ret);
> +		goto err_sysfs_remove;
> +	}
> +
> +	pr_info("Hyper-V IOMMU initialized\n");
> +
> +	return 0;
> +
> +err_sysfs_remove:
> +	iommu_device_sysfs_remove(iommup);
> +	return ret;
> +}
> +
> +void __init hv_iommu_detect(void)
> +{
> +	if (no_iommu || iommu_detected)
> +		return;
> +
> +	/* For l1vh, always expose an iommu unit */
> +	if (!hv_l1vh_partition())
> +		if (!(ms_hyperv.misc_features &
> HV_DEVICE_DOMAIN_AVAILABLE))
> +			return;
> +
> +	iommu_detected = 1;
> +	x86_init.iommu.iommu_init = hv_iommu_init;
> +
> +	pci_request_acs();
> +}
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index dfc516c1c719..2ad111727e82 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -1767,4 +1767,10 @@ static inline unsigned long virt_to_hvpfn(void
> *addr) #define HVPFN_DOWN(x)	((x) >> HV_HYP_PAGE_SHIFT)
>  #define page_to_hvpfn(page)	(page_to_pfn(page) *
> NR_HV_HYP_PAGES_IN_PAGE) 
> +#ifdef CONFIG_HYPERV_IOMMU
> +void __init hv_iommu_detect(void);
> +#else
> +static inline void hv_iommu_detect(void) { }
> +#endif /* CONFIG_HYPERV_IOMMU */
> +
>  #endif /* _HYPERV_H */

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