[bug report] GICv4.1: doorbell interrupts will be lost in a corner case

[Marc Zyngier]

On Wed, 24 Jan 2024 08:54:24 +0000,
Kunkun Jiang <jiangkunkun at huawei.com> wrote:
> 
> Hi all，
> 
> In chapter 8.5 ("Doorbells") of the GIC spec, the affinity of
> doorbell interrupt is described like this:
> 
> > Doorbell interrupts target the Redistributor the vPE is
> > currently mapped to, based on the previous VMAPP or VMOVP
> > command for the vPE.
> The doorbell interrupt here should refer to all types of
> doorbell interrupt, right?

There is only one type of doorbell.

> 
> When GICv4.1 is enabled, the doorbell interrupt will be
> truned on only when kvm handles WFI exit. There is a
> corner case where will lost doorbell interrupt:
> 1. doorbell interrupt enabled
> 2. the cpu which the vPE is mapped to is manually offline
>   through 'echo 0 > /sys/device/system/cpu/cpuX/online'
> 3. According to the description of chapter 8.5 ("Doorbells"),
>   the doorbell interrupt coming at this time will still
>   be sent to the offline cpu.Then the interrupt will be
>   lost.
> 
> Should we add a cpu offline callback to handle the
> doorbell interrupt mapped to this cpu?

That seems gross. The right way to do it is to track the affinity of
the doorbell (which we already do), and let the core code move the
interrupt somewhere else in this case (which is should already do).

Have you actually witnessed this issue? Or is that just idle
conjecture?

	M.

-- 
Without deviation from the norm, progress is not possible.