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Re: [PATCH 04/12] x86/irq: set accurate cpu_mask for high priority vectors used by external interrupts
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 20 Nov 2025 12:45:25 +0000
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- Cc: Jan Beulich <jbeulich@xxxxxxxx>
- Delivery-date: Thu, 20 Nov 2025 12:45:40 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 20/11/2025 9:06 am, Roger Pau Monne wrote:
> Setting the irq descriptor target CPU mask of high priority interrupts to
> contain all online CPUs is not accurate. External interrupts are
> exclusively delivered using physical destination mode, and hence can only
> target a single CPU. Setting the descriptor CPU mask to contain all online
> CPUs makes it impossible for Xen to figure out which CPU the interrupt is
> really targeting.
>
> Instead handle high priority vectors used by external interrupts similarly
> to normal vectors, keeping the target CPU mask accurate. Introduce
> specific code in _assign_irq_vector() to deal with moving high priority
> vectors across CPUs, this is needed at least for fixup_irqs() to be able to
> evacuate those if the target CPU goes offline.
>
> Fixes: fc0c3fa2ad5c ("x86/IO-APIC: fix setup of Xen internally used IRQs
> (take 2)")
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Which external interrupts do we have like this?
Looking at Jan's series, the VMX Posted Interrupt vector is like this,
but I can't see a case of getting a high priority vector, and
fixup_irqs() being a legitimate thing to do.
~Andrew
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