On 9/22/2026 14:42, Mukesh R wrote: > On 9/22/26 10:49, Easwar Hariharan wrote: >> On 9/21/2026 15:50, Mukesh R wrote: >>> Add a new file to implement a kernel only virtual IOMMU that works >>> with Microsoft Hyper-V hypervisor on privileged VMs aka root VMs. The >>> hypervisor claims the IOMMU upon boot, and this driver communicates with >>> it for creating and deleting paging domains, attaching of devices, mapping >>> and unmapping of pages, etc. During boot, hypervisor automatically creates >>> identity and blocked domains, so there is no need to do hypercalls to >>> create them. This is a kernel only driver and only supported on baremetal >>> root (and not L1VH root) without any guest passthru support. Support >>> for guest device passthru will be added incrementally. >>> >>> Signed-off-by: Mukesh R <[email protected]> >>> --- >>> arch/x86/kernel/pci-dma.c | 2 + >>> drivers/iommu/Kconfig | 1 + >>> drivers/iommu/hyperv/Kconfig | 15 + >>> drivers/iommu/hyperv/Makefile | 1 + >>> drivers/iommu/hyperv/hv-iommu-root.c | 645 +++++++++++++++++++++++++++ >>> include/asm-generic/mshyperv.h | 3 + >>> include/linux/hyperv.h | 6 + >>> 7 files changed, 673 insertions(+) >>> create mode 100644 drivers/iommu/hyperv/Kconfig >>> create mode 100644 drivers/iommu/hyperv/hv-iommu-root.c >>>
<snip> >>> diff --git a/drivers/iommu/hyperv/hv-iommu-root.c >>> b/drivers/iommu/hyperv/hv-iommu-root.c >>> new file mode 100644 >>> index 000000000000..a5268e0e52cc >>> --- /dev/null >>> +++ b/drivers/iommu/hyperv/hv-iommu-root.c >>> @@ -0,0 +1,645 @@ >>> +// SPDX-License-Identifier: GPL-2.0 >>> +/* >>> + * Hyper-V root vIOMMU driver. >>> + * Copyright (C) 2026, Microsoft, Inc. >>> + */ <snip> >>> + >>> +/* >>> + * 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). >>> + */ >> >> Maybe a flag, say OwnedByHyp = 1 returned for the root equivalent of the >> guest driver's >> GetLogicalDeviceProperty hypercall can solve this. > > "hypervisor does not provide list of devices it is using dynamically" Sorry, can you be more verbose? When I read this response yesterday, I thought by dynamically, you meant at runtime, but on thinking this through, the current scheme doesn't help with that either. You have to pass the kernel command-line parameter at boot because the IOMMU driver is built-in, and so if a debugger is attached to the hypervisor "at runtime", your current scheme, just like my suggestion for a flag returned by GetPhysicalDeviceProperty above, requires a reboot of the root partition. > <snip> >>> #endif /* _HYPERV_H */ >
