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Date:   Sat, 22 Aug 2020 16:19:09 +0200
From:   Jürgen Groß <>
To:     Thomas Gleixner <>,
        LKML <>
Cc:, Joerg Roedel <>,,,
        Haiyang Zhang <>,
        Jon Derrick <>,
        Lu Baolu <>,
        Wei Liu <>,
        "K. Y. Srinivasan" <>,
        Stephen Hemminger <>,
        Steve Wahl <>,
        Dimitri Sivanich <>,
        Russ Anderson <>,,
        Bjorn Helgaas <>,
        Lorenzo Pieralisi <>,
        Konrad Rzeszutek Wilk <>,,
        Boris Ostrovsky <>,
        Stefano Stabellini <>,
        Marc Zyngier <>,
        Greg Kroah-Hartman <>,
        "Rafael J. Wysocki" <>,
        Megha Dey <>,
        Jason Gunthorpe <>,
        Dave Jiang <>,
        Alex Williamson <>,
        Jacob Pan <>,
        Baolu Lu <>,
        Kevin Tian <>,
        Dan Williams <>
Subject: Re: [patch RFC 00/38] x86, PCI, XEN, genirq ...: Prepare for device

On 21.08.20 02:24, Thomas Gleixner wrote:
> First of all, sorry for the horrible long Cc list, which was
> unfortunately unavoidable as this touches the world and some more.
> This patch series aims to provide a base to support device MSI (non
> PCI based) in a halfways architecture independent way.
> It's a mixed bag of bug fixes, cleanups and general improvements which
> are worthwhile independent of the device MSI stuff. Unfortunately this
> also comes with an evil abuse of the irqdomain system to coerce XEN on
> x86 into compliance without rewriting XEN from scratch.
> As discussed in length in this mail thread:
> the initial attempt of piggypacking device MSI support on platform MSI
> is doomed for various reasons, but creating independent interrupt
> domains for these upcoming magic PCI subdevices which are not PCI, but
> might be exposed as PCI devices is not as trivial as it seems.
> The initially suggested and evaluated approach of extending platform
> MSI turned out to be the completely wrong direction and in fact
> platform MSI should be rewritten on top of device MSI or completely
> replaced by it.
> One of the main issues is that x86 does not support the concept of irq
> domains associations stored in device::msi_domain and still relies on
> the arch_*_msi_irqs() fallback implementations which has it's own set
> of problems as outlined in
> in the very same thread.
> The main obstacle of storing that pointer is XEN which has it's own
> historical notiion of handling PCI MSI interupts.
> This series tries to address these issues in several steps:
>   1) Accidental bug fixes
> 	iommu/amd: Prevent NULL pointer dereference
>   2) Janitoring
> 	x86/init: Remove unused init ops
>   3) Simplification of the x86 specific interrupt allocation mechanism
> 	x86/irq: Rename X86_IRQ_ALLOC_TYPE_MSI* to reflect PCI dependency
> 	x86/irq: Add allocation type for parent domain retrieval
> 	iommu/vt-d: Consolidate irq domain getter
> 	iommu/amd: Consolidate irq domain getter
> 	iommu/irq_remapping: Consolidate irq domain lookup
>   4) Consolidation of the X86 specific interrupt allocation mechanism to be as close
>      as possible to the generic MSI allocation mechanism which allows to get rid
>      of quite a bunch of x86'isms which are pointless
> 	x86/irq: Prepare consolidation of irq_alloc_info
> 	x86/msi: Consolidate HPET allocation
> 	x86/ioapic: Consolidate IOAPIC allocation
> 	x86/irq: Consolidate DMAR irq allocation
> 	x86/irq: Consolidate UV domain allocation
> 	PCI: MSI: Rework pci_msi_domain_calc_hwirq()
> 	x86/msi: Consolidate MSI allocation
> 	x86/msi: Use generic MSI domain ops
>    5) x86 specific cleanups to remove the dependency on arch_*_msi_irqs()
> 	x86/irq: Move apic_post_init() invocation to one place
> 	z86/pci: Reducde #ifdeffery in PCI init code
> 	x86/irq: Initialize PCI/MSI domain at PCI init time
> 	irqdomain/msi: Provide DOMAIN_BUS_VMD_MSI
> 	PCI: vmd: Mark VMD irqdomain with DOMAIN_BUS_VMD_MSI
> 	PCI: MSI: Provide pci_dev_has_special_msi_domain() helper
> 	x86/xen: Make xen_msi_init() static and rename it to xen_hvm_msi_init()
> 	x86/xen: Rework MSI teardown
> 	x86/xen: Consolidate XEN-MSI init
> 	irqdomain/msi: Allow to override msi_domain_alloc/free_irqs()
> 	x86/xen: Wrap XEN MSI management into irqdomain
> 	iommm/vt-d: Store irq domain in struct device
> 	iommm/amd: Store irq domain in struct device
> 	x86/pci: Set default irq domain in pcibios_add_device()
> 	PCI/MSI: Allow to disable arch fallbacks
> 	x86/irq: Cleanup the arch_*_msi_irqs() leftovers
> 	x86/irq: Make most MSI ops XEN private
>      This one is paving the way to device MSI support, but it comes
>      with an ugly and evil hack. The ability of overriding the default
>      allocation/free functions of an MSI irq domain is useful in general as
>      (hopefully) demonstrated with the device MSI POC, but the abuse
>      in context of XEN is evil. OTOH without enough XENology and without
>      rewriting XEN from scratch wrapping XEN MSI handling into a pseudo
>      irq domain is a reasonable step forward for mere mortals with severly
>      limited XENology. One day the XEN folks might make it a real irq domain.
>      Perhaps when they have to support the same mess on other architectures.
>      Hope dies last...
>      At least the mechanism to override alloc/free turned out to be useful
>      for implementing the base infrastructure for device MSI. So it's not a
>      completely lost case.
>    6) X86 specific preparation for device MSI
>         x86/irq: Add DEV_MSI allocation type
>         x86/msi: Let pci_msi_prepare() handle non-PCI MSI
>    7) Generic device MSI infrastructure
>         platform-msi: Provide default irq_chip:ack
>         platform-msi: Add device MSI infrastructure
>    8) Infrastructure for and a POC of an IMS (Interrupt Message
>       Storm) irq domain and irqchip implementation
>         irqdomain/msi: Provide msi_alloc/free_store() callbacks
>         irqchip: Add IMS array driver - NOT FOR MERGING
> The whole lot is also available from git:
>     git:// device-msi
> This has been tested on Intel/AMD/KVM but lacks testing on:
>      - HYPERV (-ENODEV)
>      - VMD enabled systems (-ENODEV)
>      - XEN (-ENOCLUE)

Tested to work in Xen dom0. Network is running fine with eth0 MSI
interrupts being routed through Xen.

You can add my:

Tested-by: Juergen Gross <>


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