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Re: [PATCH 04/12] x86/irq: set accurate cpu_mask for high priority vectors used by external interrupts
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 20 Nov 2025 13:53:51 +0100
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- Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 20 Nov 2025 12:54:14 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 20.11.2025 13:45, Andrew Cooper wrote:
> 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.
The serial IRQ is hiprio and wants to be subject to moving around.
Jan
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