linux-kernel - Re: [EXTERNAL] [tip: x86/apic] x86/io_apic: Cleanup trigger/polarity helpers

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Date:   Tue, 10 Nov 2020 18:50:00 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     David Woodhouse <dwmw2@...radead.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, x86 <x86@...nel.org>,
        Qian Cai <cai@...hat.com>, Joerg Roedel <joro@...tes.org>
Subject: Re: [EXTERNAL] [tip: x86/apic] x86/io_apic: Cleanup trigger/polarity helpers

On Tue, Nov 10 2020 at 16:33, David Woodhouse wrote:
> On Tue, 2020-11-10 at 10:17 -0600, Tom Lendacky wrote:
>> Yep. The warning started triggering with:
>> 47bea873cf80 ("x86/msi: Only use high bits of MSI address for DMAR unit")
>> 
>> Here's the backtrace:
>> 
>> [   15.745929]  irq_chip_compose_msi_msg+0x2e/0x40
>> [   15.750984]  msi_domain_activate+0x4b/0x90
>> [   15.755556]  __irq_domain_activate_irq+0x53/0x80
>> [   15.760707]  ? irq_set_msi_desc_off+0x5a/0x90
>> [   15.765568]  irq_domain_activate_irq+0x25/0x40
>> [   15.770525]  __msi_domain_alloc_irqs+0x16a/0x310
>> [   15.775680]  __pci_enable_msi_range+0x182/0x2b0
>> [   15.780738]  ? e820__memblock_setup+0x7d/0x7d
>> [   15.785597]  pci_enable_msi+0x16/0x30
>> [   15.789685]  iommu_init_msi+0x30/0x190
>
> It's asking the core code to generate a PCI MSI message for it and
> actually program that to the PCI device (since the IOMMU itself is a
> PCI device).
>
> That isn't actually used for generating MSI, but is instead interpreted
> to write the intcapxt registers which *do* generate the interrupts.
>
> That wants fixing, preferably not to go via MSI format at all, or maybe
> just to use the 'dmar' flag to __irq_msi_compose_msg(). Either way by
> having an irqdomain of its own like the Intel IOMMU does.
>
> If I could get post-5.5 kernels to boot at all with the AMD IOMMU
> enabled, I'd have a go at throwing that together now...

It can share the dmar domain code. Let me frob something.