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From: Thomas Gleixner <tglx@kernel.org>
To: Naman Jain <namjain@linux.microsoft.com>, Ingo Molnar
 <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, Dave Hansen
 <dave.hansen@linux.intel.com>, x86@kernel.org, "Joerg Roedel (AMD)"
 <joro@8bytes.org>, Will Deacon <will@kernel.org>, "K. Y. Srinivasan"
 <kys@microsoft.com>, Haiyang Zhang <haiyangz@microsoft.com>, Wei Liu
 <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>, Long Li
 <longli@microsoft.com>, Lorenzo Pieralisi <lpieralisi@kernel.org>,
 Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= <kwilczynski@kernel.org>, Manivannan
 Sadhasivam
 <mani@kernel.org>, Bjorn Helgaas <bhelgaas@google.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Suravee Suthikulpanit
 <suravee.suthikulpanit@amd.com>, Vasant Hegde <vasant.hegde@amd.com>,
 Robin Murphy <robin.murphy@arm.com>, Rob Herring <robh@kernel.org>,
 Shradha Gupta <shradhagupta@linux.microsoft.com>, Aditya Garg
 <gargaditya@linux.microsoft.com>, iommu@lists.linux.dev,
 linux-hyperv@vger.kernel.org, linux-pci@vger.kernel.org,
 linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/3] x86/irq, iommu/amd, PCI: Drop redundant
 irq_retrigger inits
In-Reply-To: <20260810090716.2325295-4-namjain@linux.microsoft.com>
References: <20260810090716.2325295-1-namjain@linux.microsoft.com>
 <20260810090716.2325295-4-namjain@linux.microsoft.com>
Date: Wed, 09 Sep 2026 12:24:28 +0200
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On Mon, Aug 10 2026 at 09:07, Naman Jain wrote:
> --- a/arch/x86/kernel/apic/msi.c
> +++ b/arch/x86/kernel/apic/msi.c
> @@ -137,7 +137,7 @@ msi_set_affinity(struct irq_data *irqd, const struct cpumask *mask, bool force)
>  	 * IRR.
>  	 */
>  	if (lapic_vector_set_in_irr(cfg->vector))
> -		irq_data_get_irq_chip(irqd)->irq_retrigger(irqd);
> +		irq_chip_retrigger_hierarchy(irqd);

That's broken because irqd points at the vector domain already, so there
is no parent and nothing gets retriggered.

Let's look at the hierarchy when interrupt remapping is enabled:

             | --- [DMAR]
[VECTOR] --- |                | -- [IOAPIC]
             | --- [REMAP] ---| -- [HPET]
                              | -- [DEVICE MSI]

All outer domains have .irq_set_affinity = msi_domain_set_affinity,
which does:

msi_domain_set_affinity(irqdata, ....)

    irqdata->parent->irq_set_affinity(irqdata->parent, ....);
    
In that case msi_set_affinity() is only reachable for the DMAR domain
and all others (IOAPIC, HPET, DEVICE MSI) end up in the REMAP domain
which handles irq_set_affinity and never ends up in the above code.

In the non-remapping case:

             | -- [IOAPIC]
[VECTOR] --- | -- [HPET]
             | -- [DEVICE MSI]

In this case the vector domain is the MSI parent domain for all of them
and all outer domains will end up in msi_set_affinity() via
msi_domain_set_affinity().

In any case 'irqd' in msi_set_affinity() will always point to the vector
domain and therefore the exiting code is correct and can't be changed to
retrigger hierarchy as that would see irqd->parent == NULL and do
nothing. Neither will adding a conditional there do anything useful
because the vector domain always has the retrigger callback set.

Thanks,

        tglx