Re: [PATCH v5 4/5] iommu/hyperv: Add para-virtualized IOMMU support for Hyper-V guest

[Jason Gunthorpe]

> Add a para-virtualized IOMMU driver for Linux guests running on Hyper-V.
> This driver implements stage-1 IO translation within the guest OS.
> It integrates with the Linux IOMMU core, utilizing Hyper-V hypercalls
> for:
>  - Capability discovery
>  - Domain allocation, configuration, and deallocation
>  - Device attachment and detachment
>  - IOTLB invalidation
> 
> The driver constructs x86-compatible stage-1 IO page tables in the
> guest memory using consolidated IO page table helpers. This allows
> the guest to manage stage-1 translations independently of vendor-
> specific drivers (like Intel VT-d or AMD IOMMU).
> 
> Hyper-V consumes this stage-1 IO page table when a device domain is
> created and configured, and nests it with the host's stage-2 IO page
> tables, therefore eliminating the VM exits for guest IOMMU mapping
> operations. For unmapping operations, VM exits to perform the IOTLB
> flush are still unavoidable.
> 
> Guest hibernation and resume are not supported by this initial
> implementation. The guest-owned stage-1 page tables reside in guest
> memory and are preserved in the hibernation image. However, the image
> does not by itself preserve the Hyper-V device-domain objects or their
> device attachments, and the current pvIOMMU interface does not define
> whether or how Hyper-V restores that state.
> 
> To identify a device in its hypercall interface, the driver looks up the
> logical device ID prefix registered for the device's PCI domain (see the
> logical device ID registry in hv_common.c) and combines it with the PCI
> function number of the endpoint device.
> 
> Co-developed-by: Wei Liu <wei.liu@xxxxxxxxxx>
> Signed-off-by: Wei Liu <wei.liu@xxxxxxxxxx>
> Co-developed-by: Easwar Hariharan <easwar.hariharan@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Easwar Hariharan <easwar.hariharan@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Yu Zhang <zhangyu1@xxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Jacob Pan <jacob.pan@xxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
> ---
>  arch/x86/hyperv/hv_init.c             |   4 +
>  arch/x86/include/asm/mshyperv.h       |   4 +
>  drivers/iommu/Kconfig                 |   1 +
>  drivers/iommu/hyperv/Kconfig          |  16 +
>  drivers/iommu/hyperv/Makefile         |   1 +
>  drivers/iommu/hyperv/hv-iommu-guest.c | 607 ++++++++++++++++++++++++++
>  drivers/iommu/hyperv/iommu.h          |  44 ++
>  7 files changed, 677 insertions(+)
>  create mode 100644 drivers/iommu/hyperv/Kconfig
>  create mode 100644 drivers/iommu/hyperv/hv-iommu-guest.c
>  create mode 100644 drivers/iommu/hyperv/iommu.h
>
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 0b4a1c0b0b16fb..d5edc853096436 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -579,6 +579,10 @@ void __init hyperv_init(void)
>  	old_setup_percpu_clockev = x86_init.timers.setup_percpu_clockev;
>  	x86_init.timers.setup_percpu_clockev = hv_stimer_setup_percpu_clockev;
>  
> +#ifdef CONFIG_HYPERV_PVIOMMU
> +	x86_init.iommu.iommu_init = hv_iommu_init;
> +#endif
> +
>  	hv_apic_init();
>  
>  	x86_init.pci.arch_init = hv_pci_init;
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index f64393e853ee31..20d947c2c758b0 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -313,6 +313,10 @@ static inline void mshv_vtl_return_hypercall(void) {}
>  static inline void __mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0) {}
>  #endif
>  
> +#ifdef CONFIG_HYPERV_PVIOMMU
> +int __init hv_iommu_init(void);
> +#endif
> +
>  #include <asm-generic/mshyperv.h>
>  
>  #endif
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 6e07bd69467a3d..0d128f377929f4 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -195,6 +195,7 @@ config MSM_IOMMU
>  source "drivers/iommu/amd/Kconfig"
>  source "drivers/iommu/arm/Kconfig"
>  source "drivers/iommu/intel/Kconfig"
> +source "drivers/iommu/hyperv/Kconfig"
>  source "drivers/iommu/iommufd/Kconfig"
>  source "drivers/iommu/riscv/Kconfig"
>  
> diff --git a/drivers/iommu/hyperv/Kconfig b/drivers/iommu/hyperv/Kconfig
> new file mode 100644
> index 00000000000000..dd8900700b85ad
> --- /dev/null
> +++ b/drivers/iommu/hyperv/Kconfig
> @@ -0,0 +1,16 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +# Hyper-V para-virtualized IOMMU driver for Linux guests
> +config HYPERV_PVIOMMU
> +	bool "Microsoft Hyper-V para-virtualized IOMMU driver for Linux guests"
> +	depends on X86_64 && HYPERV
> +	select IOMMU_API
> +	select GENERIC_PT
> +	select IOMMU_PT
> +	select IOMMU_PT_X86_64
> +	select IOMMU_IOVA

Should this be IOMMU_DMA ?

> [ ... 389 lines skipped ... ]
> +static void hv_iommu_get_resv_regions(struct device *dev,
> +				      struct list_head *head)
> +{
> +	struct iommu_resv_region *region;
> +
> +	region = iommu_alloc_resv_x86_msi_region();
> +	if (!region)
> +		return;
> +
> +	list_add_tail(&region->list, head);
> +}

Maybe the helper should have added to the list too?

It broadly seems OK to me

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

-- 
Jason