* Re: [PATCH V2 09/11] x86/hyperv: Implement hyperv virtual IOMMU
[not found] ` <20260501004157.3108202-10-mrathor@linux.microsoft.com>
@ 2026-05-06 10:07 ` Souradeep Chakrabarti
2026-05-08 1:54 ` Mukesh R
0 siblings, 1 reply; 2+ messages in thread
From: Souradeep Chakrabarti @ 2026-05-06 10:07 UTC (permalink / raw)
To: Mukesh R
Cc: hpa, robin.murphy, robh, wei.liu, mhklinux, muislam, namjain,
magnuskulke, anbelski, linux-kernel, linux-hyperv, iommu,
linux-pci, linux-arch, kys, haiyangz, decui, longli, tglx, mingo,
bp, dave.hansen, x86, joro, will, lpieralisi, kwilczynski,
bhelgaas, arnd
On Thu, Apr 30, 2026 at 05:41:55PM -0700, Mukesh R wrote:
> 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 baremetal root
> or L1VH root. This also implements direct attach mechanism (see below),
> a special feature of Hyper-V 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 (aka Domain Attach): root must create a device domain
> in the hypervisor, and do map/unmap hypercalls for mapping and
> unmapping guest RAM for DMA. 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 root need not map/unmap guest
> memory for DMA. As such, direct attach passthru setup during guest
> boot is extremely fast. A direct attached device must always be
> referenced via logical device ID and not via the PCI device ID.
>
> At present, L1VH root only supports direct attaches. Also direct attach is
> default in non-L1VH cases because there are some significant performance
> issues with domain attach implementations currently for guests with higher
> RAM (say more than 8GB), and that unfortunately cannot be addressed in
> the short term.
>
> Co-developed-by: Wei Liu <wei.liu@kernel.org>
> Signed-off-by: Wei Liu <wei.liu@kernel.org>
> Signed-off-by: Mukesh R <mrathor@linux.microsoft.com>
> ---
> MAINTAINERS | 1 +
> arch/x86/kernel/pci-dma.c | 2 +
> drivers/iommu/Kconfig | 5 +-
> drivers/iommu/Makefile | 1 +
> drivers/iommu/hyperv-iommu-root.c | 908 ++++++++++++++++++++++++++++++
> include/asm-generic/mshyperv.h | 17 +
> include/linux/hyperv.h | 6 +
> 7 files changed, 937 insertions(+), 3 deletions(-)
> create mode 100644 drivers/iommu/hyperv-iommu-root.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index f803a6a38fee..8ae040b89a56 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -11914,6 +11914,7 @@ F: drivers/clocksource/hyperv_timer.c
> F: drivers/hid/hid-hyperv.c
> F: drivers/hv/
> F: drivers/input/serio/hyperv-keyboard.c
> +F: drivers/iommu/hyperv-iommu-root.c
> F: drivers/iommu/hyperv-irq.c
> F: drivers/net/ethernet/microsoft/
> F: drivers/net/hyperv/
> 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();
> swiotlb_init(x86_swiotlb_enable, x86_swiotlb_flags);
> }
>
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index f86262b11416..7909cf4373a6 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -352,13 +352,12 @@ config MTK_IOMMU_V1
> if unsure, say N here.
>
> config HYPERV_IOMMU
> - bool "Hyper-V IRQ Handling"
> + bool "Hyper-V IOMMU Unit"
> depends on HYPERV && X86
> select IOMMU_API
> default HYPERV
> help
> - Stub IOMMU driver to handle IRQs to support Hyper-V Linux
> - guest and root partitions.
> + Hyper-V pseudo IOMMU unit.
>
> config VIRTIO_IOMMU
> tristate "Virtio IOMMU driver"
> diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
> index 335ea77cced6..296fbc6ca829 100644
> --- a/drivers/iommu/Makefile
> +++ b/drivers/iommu/Makefile
> @@ -31,6 +31,7 @@ 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) += hyperv-irq.o
> +obj-$(CONFIG_HYPERV_IOMMU) += hyperv-iommu-root.o
> obj-$(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-root.c b/drivers/iommu/hyperv-iommu-root.c
> new file mode 100644
> index 000000000000..739bbf39dea2
> --- /dev/null
> +++ b/drivers/iommu/hyperv-iommu-root.c
> @@ -0,0 +1,908 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Hyper-V root vIOMMU driver.
> + * Copyright (C) 2026, Microsoft, Inc.
> + */
> +
> +#include <linux/pci.h>
> +#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 */
> + bool attached_dom; /* is this direct attached dom? */
> + u64 partid; /* partition id */
> + 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 domains to correspond to hypervisor prebuilt default identity
> + * and null domains (dummy because we do not make hypercalls to create them).
> + */
> +static struct hv_domain hv_def_identity_dom;
> +static struct hv_domain hv_null_dom;
> +
> +static bool hv_special_domain(struct hv_domain *hvdom)
> +{
> + return hvdom == &hv_def_identity_dom || hvdom == &hv_null_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_get_current_partid(void)
> +{
> + u64 (*fn)(void);
> + u64 ptid;
> +
> + fn = symbol_get(mshv_current_partid);
> + if (!fn)
> + return HV_PARTITION_ID_INVALID;
> +
> + ptid = fn();
> + symbol_put(mshv_current_partid);
> +
> + return ptid;
> +}
> +EXPORT_SYMBOL_GPL(hv_get_current_partid);
> +
> +/* If this is a VMM thread, then this domain is for a guest vm */
> +static bool hv_curr_thread_is_vmm(void)
> +{
> + return hv_get_current_partid() != HV_PARTITION_ID_INVALID;
> +}
> +
> +/* As opposed to some host app like SPDK etc... */
> +static bool hv_dom_owner_is_vmm(struct hv_domain *hvdom)
> +{
> + return hvdom && hvdom->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;
> + }
> +}
> +
> +/*
> + * 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);
> +
> +bool hv_pcidev_is_pthru_dev(struct pci_dev *pdev)
> +{
> + struct device *dev = &pdev->dev;
> + struct hv_domain *hvdom = dev_iommu_priv_get(dev);
> +
> + if (hvdom && !hv_special_domain(hvdom))
> + return true;
> +
> + return false;
> +}
> +EXPORT_SYMBOL_GPL(hv_pcidev_is_pthru_dev);
> +
> +/* Build device id for direct attached devices */
> +static u64 hv_build_devid_type_logical(struct pci_dev *pdev)
> +{
> + hv_pci_segment segment;
> + union hv_device_id hv_devid;
> + union hv_pci_bdf bdf = {.as_uint16 = 0};
> + u32 rid = PCI_DEVID(pdev->bus->number, pdev->devfn);
> +
> + segment = pci_domain_nr(pdev->bus);
> + bdf.bus = PCI_BUS_NUM(rid);
> + bdf.device = PCI_SLOT(rid);
> + bdf.function = PCI_FUNC(rid);
> +
> + hv_devid.as_uint64 = 0;
> + hv_devid.device_type = HV_DEVICE_TYPE_LOGICAL;
> + hv_devid.logical.id = (u64)segment << 16 | bdf.as_uint16;
> +
> + return hv_devid.as_uint64;
> +}
> +
> +u64 hv_build_devid_oftype(struct pci_dev *pdev, enum hv_device_type type)
> +{
> + if (type == HV_DEVICE_TYPE_LOGICAL) {
> + if (hv_l1vh_partition())
> + return hv_pci_vmbus_device_id(pdev);
> + else
> + return hv_build_devid_type_logical(pdev);
> + } else if (type == HV_DEVICE_TYPE_PCI)
> +#ifdef CONFIG_X86
> + return hv_build_devid_type_pci(pdev);
> +#else
> + return 0;
> +#endif
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(hv_build_devid_oftype);
> +
> +/* Create a new device domain in the hypervisor */
> +static int hv_iommu_create_hyp_devdom(struct hv_domain *hvdom)
> +{
> + u64 status;
> + struct hv_input_device_domain *ddp;
> + struct hv_input_create_device_domain *input;
> + unsigned long flags;
> +
> + 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);
> +}
> +
> +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()) {
> + pr_err("Hyper-V: l1vh iommu does not support host devices\n");
> + return NULL;
> + }
> +
> + hvdom = kzalloc(sizeof(struct hv_domain), GFP_KERNEL);
> + if (hvdom == NULL)
> + return NULL;
> +
> + spin_lock_init(&hvdom->mappings_lock);
> + hvdom->mappings_tree = RB_ROOT_CACHED;
> +
> + /* Called under iommu group mutex, so single threaded */
> + if (++unique_id == HV_DEVICE_DOMAIN_ID_S2_DEFAULT) /* ie, 0 */
> + goto out_err;
> +
> + hvdom->domid_num = unique_id;
> + hvdom->partid = hv_get_current_partid();
> + 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_dom_owner_is_vmm(hvdom) && !hv_no_attdev)
> + hvdom->attached_dom = true;
> + else {
> + rc = hv_iommu_create_hyp_devdom(hvdom);
> + if (rc)
> + goto out_err;
> + }
> +
> + return &hvdom->iommu_dom;
> +
> +out_err:
> + unique_id--;
> + kfree(hvdom);
> + 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 (!hv_dom_owner_is_vmm(hvdom) || 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");
> + }
> +
> + 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, u64 ptid)
> +{
> + 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;
> +
> + 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);
This can become a infinite loop, if for some reason HV continue to fail
to attach device for some other reason than insufficient memory. We can
have a max retry count here.
> +
> + if (!hv_result_success(status))
> + hv_status_err(status, "\n");
> +
> + return hv_result_to_errno(status);
> +}
> +
> +/* Attach a device for passthru to guest VMs, host apps like SPDK, etc */
> +static int hv_iommu_attach_dev(struct iommu_domain *immdom, struct device *dev,
> + struct iommu_domain *old)
> +{
> + 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);
> +
> + 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, hvdom_new->partid);
> + else
> + rc = hv_iommu_att_dev2dom(hvdom_new, pdev);
destructive detach before failable attach with no rollback.
1. If hvdom_prev exists, issue HVCALL_DETACH_DEVICE_DOMAIN /
HVCALL_DETACH_DEVICE against the old hypervisor domain.
2. Then issue the attach hypercall against the new domain
3. Only on success, update dev_iommu_priv.
If step 2 fails, the device is left hypervisor-detached while
dev_iommu_priv still points at the old domain, and the IOMMU core's
recovery does not help
> +
> + if (rc == 0)
> + dev_iommu_priv_set(dev, hvdom_new); /* sets "private" field */
> +
> + return rc;
> +}
> +
> +static void hv_iommu_det_dev_from_guest(struct pci_dev *pdev, u64 ptid)
> +{
> + 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 = ptid;
> + 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 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;
> +
> + pdev = to_pci_dev(dev);
> +
> + if (hvdom->attached_dom)
> + hv_iommu_det_dev_from_guest(pdev, hvdom->partid);
> +
> + /* Do not reset attached_dom, hv_iommu_unmap_pages happens
> + * next.
> + */
> + else
> + hv_iommu_det_dev_from_dom(pdev);
> +}
> +
> +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;
> +
> + 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;
No boundary check for npages here in gpa_page_list, as 512 PFNs in the
pfn array is the limit for the rep hypercall.
> +
> + status = hv_do_rep_hypercall(HVCALL_MAP_DEVICE_GPA_PAGES, npages, 0,
> + input, NULL);
npages can get trucated here, as rep_count is u16.
> +
> + 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;
> + continue;
> + }
> + 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, HV_HYP_PAGE_SIZE,
> + 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);
npages can get truncated here.
> + 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)
> +{
> + unsigned long flags;
> + struct hv_iommu_mapping *mapping;
> + struct interval_tree_node *node;
> + u64 paddr = 0;
> + 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, immdom);
> + 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_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,
> + .identity_domain = &hv_def_identity_dom.iommu_dom,
> + .blocked_domain = &hv_null_dom.iommu_dom,
> +};
> +
> +static const struct iommu_domain_ops hv_special_domain_ops = {
> + .attach_dev = hv_iommu_attach_dev,
> +};
> +
> +static void __init hv_initialize_special_domains(void)
> +{
> + hv_def_identity_dom.iommu_dom.type = IOMMU_DOMAIN_IDENTITY;
> + hv_def_identity_dom.iommu_dom.ops = &hv_special_domain_ops;
> + hv_def_identity_dom.iommu_dom.owner = &hv_iommu_ops;
> + hv_def_identity_dom.iommu_dom.geometry = default_geometry;
> + hv_def_identity_dom.domid_num = HV_DEVICE_DOMAIN_ID_S2_DEFAULT; /* 0 */
> +
> + hv_null_dom.iommu_dom.type = IOMMU_DOMAIN_BLOCKED;
> + hv_null_dom.iommu_dom.ops = &hv_special_domain_ops;
> + hv_null_dom.iommu_dom.owner = &hv_iommu_ops;
> + hv_null_dom.iommu_dom.geometry = default_geometry;
> + hv_null_dom.domid_num = HV_DEVICE_DOMAIN_ID_S2_NULL; /* INTMAX */
> +}
> +
> +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/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index a6878ab685e7..fca5ed68b5c2 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -337,6 +337,23 @@ static inline u64 hv_pci_vmbus_device_id(struct pci_dev *pdev)
> { return 0; }
> #endif /* IS_ENABLED(CONFIG_PCI_HYPERV) */
>
> +#if IS_ENABLED(CONFIG_HYPERV_IOMMU)
> +u64 hv_get_current_partid(void);
> +bool hv_pcidev_is_attached_dev(struct pci_dev *pdev);
> +bool hv_pcidev_is_pthru_dev(struct pci_dev *pdev);
> +u64 hv_build_devid_oftype(struct pci_dev *pdev, enum hv_device_type type);
> +#else
> +static inline bool hv_pcidev_is_attached_dev(struct pci_dev *pdev)
> +{ return false; }
> +static inline bool hv_pcidev_is_pthru_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_get_current_partid(void)
> +{ return HV_PARTITION_ID_INVALID; }
> +#endif /* IS_ENABLED(CONFIG_HYPERV_IOMMU) */
> +
> #if IS_ENABLED(CONFIG_MSHV_ROOT)
> static inline bool hv_root_partition(void)
> {
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index 5459e776ec17..6eee1cbf6f23 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -1769,4 +1769,10 @@ 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 */
> --
> 2.51.2.vfs.0.1
>
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH V2 09/11] x86/hyperv: Implement hyperv virtual IOMMU
2026-05-06 10:07 ` [PATCH V2 09/11] x86/hyperv: Implement hyperv virtual IOMMU Souradeep Chakrabarti
@ 2026-05-08 1:54 ` Mukesh R
0 siblings, 0 replies; 2+ messages in thread
From: Mukesh R @ 2026-05-08 1:54 UTC (permalink / raw)
To: Souradeep Chakrabarti
Cc: hpa, robin.murphy, robh, wei.liu, mhklinux, muislam, namjain,
magnuskulke, anbelski, linux-kernel, linux-hyperv, iommu,
linux-pci, linux-arch, kys, haiyangz, decui, longli, tglx, mingo,
bp, dave.hansen, x86, joro, will, lpieralisi, kwilczynski,
bhelgaas, arnd
On 5/6/26 03:07, Souradeep Chakrabarti wrote:
> On Thu, Apr 30, 2026 at 05:41:55PM -0700, Mukesh R wrote:
>> 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 baremetal root
>> or L1VH root. This also implements direct attach mechanism (see below),
>> a special feature of Hyper-V 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 (aka Domain Attach): root must create a device domain
>> in the hypervisor, and do map/unmap hypercalls for mapping and
>> unmapping guest RAM for DMA. 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 root need not map/unmap guest
>> memory for DMA. As such, direct attach passthru setup during guest
>> boot is extremely fast. A direct attached device must always be
>> referenced via logical device ID and not via the PCI device ID.
>>
>> At present, L1VH root only supports direct attaches. Also direct attach is
>> default in non-L1VH cases because there are some significant performance
>> issues with domain attach implementations currently for guests with higher
>> RAM (say more than 8GB), and that unfortunately cannot be addressed in
>> the short term.
>>
>> Co-developed-by: Wei Liu <wei.liu@kernel.org>
>> Signed-off-by: Wei Liu <wei.liu@kernel.org>
>> Signed-off-by: Mukesh R <mrathor@linux.microsoft.com>
>> ---
>> MAINTAINERS | 1 +
>> arch/x86/kernel/pci-dma.c | 2 +
>> drivers/iommu/Kconfig | 5 +-
>> drivers/iommu/Makefile | 1 +
>> drivers/iommu/hyperv-iommu-root.c | 908 ++++++++++++++++++++++++++++++
>> include/asm-generic/mshyperv.h | 17 +
>> include/linux/hyperv.h | 6 +
>> 7 files changed, 937 insertions(+), 3 deletions(-)
>> create mode 100644 drivers/iommu/hyperv-iommu-root.c
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index f803a6a38fee..8ae040b89a56 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -11914,6 +11914,7 @@ F: drivers/clocksource/hyperv_timer.c
>> F: drivers/hid/hid-hyperv.c
>> F: drivers/hv/
>> F: drivers/input/serio/hyperv-keyboard.c
>> +F: drivers/iommu/hyperv-iommu-root.c
>> F: drivers/iommu/hyperv-irq.c
>> F: drivers/net/ethernet/microsoft/
>> F: drivers/net/hyperv/
>> 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();
>> swiotlb_init(x86_swiotlb_enable, x86_swiotlb_flags);
>> }
>>
>> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
>> index f86262b11416..7909cf4373a6 100644
>> --- a/drivers/iommu/Kconfig
>> +++ b/drivers/iommu/Kconfig
>> @@ -352,13 +352,12 @@ config MTK_IOMMU_V1
>> if unsure, say N here.
>>
>> config HYPERV_IOMMU
>> - bool "Hyper-V IRQ Handling"
>> + bool "Hyper-V IOMMU Unit"
>> depends on HYPERV && X86
>> select IOMMU_API
>> default HYPERV
>> help
>> - Stub IOMMU driver to handle IRQs to support Hyper-V Linux
>> - guest and root partitions.
>> + Hyper-V pseudo IOMMU unit.
>>
>> config VIRTIO_IOMMU
>> tristate "Virtio IOMMU driver"
>> diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
>> index 335ea77cced6..296fbc6ca829 100644
>> --- a/drivers/iommu/Makefile
>> +++ b/drivers/iommu/Makefile
>> @@ -31,6 +31,7 @@ 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) += hyperv-irq.o
>> +obj-$(CONFIG_HYPERV_IOMMU) += hyperv-iommu-root.o
>> obj-$(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-root.c b/drivers/iommu/hyperv-iommu-root.c
>> new file mode 100644
>> index 000000000000..739bbf39dea2
>> --- /dev/null
>> +++ b/drivers/iommu/hyperv-iommu-root.c
>> @@ -0,0 +1,908 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Hyper-V root vIOMMU driver.
>> + * Copyright (C) 2026, Microsoft, Inc.
>> + */
>> +
>> +#include <linux/pci.h>
>> +#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 */
>> + bool attached_dom; /* is this direct attached dom? */
>> + u64 partid; /* partition id */
>> + 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 domains to correspond to hypervisor prebuilt default identity
>> + * and null domains (dummy because we do not make hypercalls to create them).
>> + */
>> +static struct hv_domain hv_def_identity_dom;
>> +static struct hv_domain hv_null_dom;
>> +
>> +static bool hv_special_domain(struct hv_domain *hvdom)
>> +{
>> + return hvdom == &hv_def_identity_dom || hvdom == &hv_null_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_get_current_partid(void)
>> +{
>> + u64 (*fn)(void);
>> + u64 ptid;
>> +
>> + fn = symbol_get(mshv_current_partid);
>> + if (!fn)
>> + return HV_PARTITION_ID_INVALID;
>> +
>> + ptid = fn();
>> + symbol_put(mshv_current_partid);
>> +
>> + return ptid;
>> +}
>> +EXPORT_SYMBOL_GPL(hv_get_current_partid);
>> +
>> +/* If this is a VMM thread, then this domain is for a guest vm */
>> +static bool hv_curr_thread_is_vmm(void)
>> +{
>> + return hv_get_current_partid() != HV_PARTITION_ID_INVALID;
>> +}
>> +
>> +/* As opposed to some host app like SPDK etc... */
>> +static bool hv_dom_owner_is_vmm(struct hv_domain *hvdom)
>> +{
>> + return hvdom && hvdom->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;
>> + }
>> +}
>> +
>> +/*
>> + * 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);
>> +
>> +bool hv_pcidev_is_pthru_dev(struct pci_dev *pdev)
>> +{
>> + struct device *dev = &pdev->dev;
>> + struct hv_domain *hvdom = dev_iommu_priv_get(dev);
>> +
>> + if (hvdom && !hv_special_domain(hvdom))
>> + return true;
>> +
>> + return false;
>> +}
>> +EXPORT_SYMBOL_GPL(hv_pcidev_is_pthru_dev);
>> +
>> +/* Build device id for direct attached devices */
>> +static u64 hv_build_devid_type_logical(struct pci_dev *pdev)
>> +{
>> + hv_pci_segment segment;
>> + union hv_device_id hv_devid;
>> + union hv_pci_bdf bdf = {.as_uint16 = 0};
>> + u32 rid = PCI_DEVID(pdev->bus->number, pdev->devfn);
>> +
>> + segment = pci_domain_nr(pdev->bus);
>> + bdf.bus = PCI_BUS_NUM(rid);
>> + bdf.device = PCI_SLOT(rid);
>> + bdf.function = PCI_FUNC(rid);
>> +
>> + hv_devid.as_uint64 = 0;
>> + hv_devid.device_type = HV_DEVICE_TYPE_LOGICAL;
>> + hv_devid.logical.id = (u64)segment << 16 | bdf.as_uint16;
>> +
>> + return hv_devid.as_uint64;
>> +}
>> +
>> +u64 hv_build_devid_oftype(struct pci_dev *pdev, enum hv_device_type type)
>> +{
>> + if (type == HV_DEVICE_TYPE_LOGICAL) {
>> + if (hv_l1vh_partition())
>> + return hv_pci_vmbus_device_id(pdev);
>> + else
>> + return hv_build_devid_type_logical(pdev);
>> + } else if (type == HV_DEVICE_TYPE_PCI)
>> +#ifdef CONFIG_X86
>> + return hv_build_devid_type_pci(pdev);
>> +#else
>> + return 0;
>> +#endif
>> + return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(hv_build_devid_oftype);
>> +
>> +/* Create a new device domain in the hypervisor */
>> +static int hv_iommu_create_hyp_devdom(struct hv_domain *hvdom)
>> +{
>> + u64 status;
>> + struct hv_input_device_domain *ddp;
>> + struct hv_input_create_device_domain *input;
>> + unsigned long flags;
>> +
>> + 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);
>> +}
>> +
>> +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()) {
>> + pr_err("Hyper-V: l1vh iommu does not support host devices\n");
>> + return NULL;
>> + }
>> +
>> + hvdom = kzalloc(sizeof(struct hv_domain), GFP_KERNEL);
>> + if (hvdom == NULL)
>> + return NULL;
>> +
>> + spin_lock_init(&hvdom->mappings_lock);
>> + hvdom->mappings_tree = RB_ROOT_CACHED;
>> +
>> + /* Called under iommu group mutex, so single threaded */
>> + if (++unique_id == HV_DEVICE_DOMAIN_ID_S2_DEFAULT) /* ie, 0 */
>> + goto out_err;
>> +
>> + hvdom->domid_num = unique_id;
>> + hvdom->partid = hv_get_current_partid();
>> + 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_dom_owner_is_vmm(hvdom) && !hv_no_attdev)
>> + hvdom->attached_dom = true;
>> + else {
>> + rc = hv_iommu_create_hyp_devdom(hvdom);
>> + if (rc)
>> + goto out_err;
>> + }
>> +
>> + return &hvdom->iommu_dom;
>> +
>> +out_err:
>> + unique_id--;
>> + kfree(hvdom);
>> + 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 (!hv_dom_owner_is_vmm(hvdom) || 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");
>> + }
>> +
>> + 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, u64 ptid)
>> +{
>> + 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;
>> +
>> + 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);
> This can become a infinite loop, if for some reason HV continue to fail
> to attach device for some other reason than insufficient memory. We can
> have a max retry count here.
I don't understand. do while will exit if status is not insuff memory,
right?
>> +
>> + if (!hv_result_success(status))
>> + hv_status_err(status, "\n");
>> +
>> + return hv_result_to_errno(status);
>> +}
>> +
>> +/* Attach a device for passthru to guest VMs, host apps like SPDK, etc */
>> +static int hv_iommu_attach_dev(struct iommu_domain *immdom, struct device *dev,
>> + struct iommu_domain *old)
>> +{
>> + 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);
>> +
>> + 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, hvdom_new->partid);
>> + else
>> + rc = hv_iommu_att_dev2dom(hvdom_new, pdev);
> destructive detach before failable attach with no rollback.
> 1. If hvdom_prev exists, issue HVCALL_DETACH_DEVICE_DOMAIN /
> HVCALL_DETACH_DEVICE against the old hypervisor domain.
> 2. Then issue the attach hypercall against the new domain
> 3. Only on success, update dev_iommu_priv.
>
> If step 2 fails, the device is left hypervisor-detached while
> dev_iommu_priv still points at the old domain, and the IOMMU core's
> recovery does not help
Yeah, the error will cause either boot to fail or vmm to abort. Worst
case would be to detach again, but I suppose we could just set to NULL.
>> +
>> + if (rc == 0)
>> + dev_iommu_priv_set(dev, hvdom_new); /* sets "private" field */
>> +
>> + return rc;
>> +}
>> +
>> +static void hv_iommu_det_dev_from_guest(struct pci_dev *pdev, u64 ptid)
>> +{
>> + 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 = ptid;
>> + 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 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;
>> +
>> + pdev = to_pci_dev(dev);
>> +
>> + if (hvdom->attached_dom)
>> + hv_iommu_det_dev_from_guest(pdev, hvdom->partid);
>> +
>> + /* Do not reset attached_dom, hv_iommu_unmap_pages happens
>> + * next.
>> + */
>> + else
>> + hv_iommu_det_dev_from_dom(pdev);
>> +}
>> +
>> +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;
>> +
>> + 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;
> No boundary check for npages here in gpa_page_list, as 512 PFNs in the
> pfn array is the limit for the rep hypercall.
Not needed. Like the comment above says:
/*
* 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)
We plan for it.
>> +
>> + status = hv_do_rep_hypercall(HVCALL_MAP_DEVICE_GPA_PAGES, npages, 0,
>> + input, NULL);
> npages can get trucated here, as rep_count is u16.
See above.
Thanks,
-Mukesh
>> +
>> + 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;
>> + continue;
>> + }
>> + 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, HV_HYP_PAGE_SIZE,
>> + 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);
> npages can get truncated here.
>> + 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)
>> +{
>> + unsigned long flags;
>> + struct hv_iommu_mapping *mapping;
>> + struct interval_tree_node *node;
>> + u64 paddr = 0;
>> + 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, immdom);
>> + 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_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,
>> + .identity_domain = &hv_def_identity_dom.iommu_dom,
>> + .blocked_domain = &hv_null_dom.iommu_dom,
>> +};
>> +
>> +static const struct iommu_domain_ops hv_special_domain_ops = {
>> + .attach_dev = hv_iommu_attach_dev,
>> +};
>> +
>> +static void __init hv_initialize_special_domains(void)
>> +{
>> + hv_def_identity_dom.iommu_dom.type = IOMMU_DOMAIN_IDENTITY;
>> + hv_def_identity_dom.iommu_dom.ops = &hv_special_domain_ops;
>> + hv_def_identity_dom.iommu_dom.owner = &hv_iommu_ops;
>> + hv_def_identity_dom.iommu_dom.geometry = default_geometry;
>> + hv_def_identity_dom.domid_num = HV_DEVICE_DOMAIN_ID_S2_DEFAULT; /* 0 */
>> +
>> + hv_null_dom.iommu_dom.type = IOMMU_DOMAIN_BLOCKED;
>> + hv_null_dom.iommu_dom.ops = &hv_special_domain_ops;
>> + hv_null_dom.iommu_dom.owner = &hv_iommu_ops;
>> + hv_null_dom.iommu_dom.geometry = default_geometry;
>> + hv_null_dom.domid_num = HV_DEVICE_DOMAIN_ID_S2_NULL; /* INTMAX */
>> +}
>> +
>> +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/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
>> index a6878ab685e7..fca5ed68b5c2 100644
>> --- a/include/asm-generic/mshyperv.h
>> +++ b/include/asm-generic/mshyperv.h
>> @@ -337,6 +337,23 @@ static inline u64 hv_pci_vmbus_device_id(struct pci_dev *pdev)
>> { return 0; }
>> #endif /* IS_ENABLED(CONFIG_PCI_HYPERV) */
>>
>> +#if IS_ENABLED(CONFIG_HYPERV_IOMMU)
>> +u64 hv_get_current_partid(void);
>> +bool hv_pcidev_is_attached_dev(struct pci_dev *pdev);
>> +bool hv_pcidev_is_pthru_dev(struct pci_dev *pdev);
>> +u64 hv_build_devid_oftype(struct pci_dev *pdev, enum hv_device_type type);
>> +#else
>> +static inline bool hv_pcidev_is_attached_dev(struct pci_dev *pdev)
>> +{ return false; }
>> +static inline bool hv_pcidev_is_pthru_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_get_current_partid(void)
>> +{ return HV_PARTITION_ID_INVALID; }
>> +#endif /* IS_ENABLED(CONFIG_HYPERV_IOMMU) */
>> +
>> #if IS_ENABLED(CONFIG_MSHV_ROOT)
>> static inline bool hv_root_partition(void)
>> {
>> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
>> index 5459e776ec17..6eee1cbf6f23 100644
>> --- a/include/linux/hyperv.h
>> +++ b/include/linux/hyperv.h
>> @@ -1769,4 +1769,10 @@ 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 */
>> --
>> 2.51.2.vfs.0.1
>>
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[not found] <20260501004157.3108202-1-mrathor@linux.microsoft.com>
[not found] ` <20260501004157.3108202-10-mrathor@linux.microsoft.com>
2026-05-06 10:07 ` [PATCH V2 09/11] x86/hyperv: Implement hyperv virtual IOMMU Souradeep Chakrabarti
2026-05-08 1:54 ` Mukesh R
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