Re: [PATCH v2] KVM: arm64: vgic: Do not remove in-flight LPIs from AP list on disable

[Yuchao Zhang]

Hi Fuad,

Thanks a lot for pointing me to that thread! I was not aware of
Hyunwoo's earlier report and the discussion with Oliver and Marc.

I'll read through the thread and their rationale on the ap_list_lock
approach. I'm happy to defer to Hyunwoo's effort to avoid duplicate
work.

Thanks again for the pointer!

Best regards,
Yuchao

Fuad Tabba <fuad.tabba@xxxxxxxxx> 于2026年9月18日周五 15:22写道：
>
> Hi Yuchao,
>
> On Fri, 18 Sep 2026 12:02:14 +0800, Yuchao Zhang <ndaugoing@xxxxxxxxx> wrote:
>
> [...]
>
> > Note: this closes the primary race (the last_lr_irq node itself is no
> > longer unlinkable while in-flight), but the fold traversal can still
> > race with a remote flush unlinking a subsequent non-LR node in the
> > ap_list tail. Fully closing that window needs the fold side to take
> > references before dropping locks (in the spirit of the prune-side fix
> > in commit 7258770e5814 ("KVM: arm64: vgic: Handle race between
> > interrupt affinity change and LPI disabling")) and is left as a
> > follow-up.
>
> This is the same race Hyunwoo reported back in June [1]. You might
> want to have a look at that thread first: Oliver and Marc's view there
> was that the fix is to take the ap_list_lock in
> vgic_v3_fold_lr_state() [2][3], and Hyunwoo posted a draft of that
> [4].
>
> Cheers,
> /fuad
>
> [1] https://lore.kernel.org/r/aiHrGM1f8czcUby4@v4bel
> [2] https://lore.kernel.org/r/aiJi5a3JJ-TbWL-s@xxxxxxxxxx
> [3] https://lore.kernel.org/r/87a4t99z9n.wl-maz@xxxxxxxxxx
> [4] https://lore.kernel.org/r/aiXvwGD1hS6vwLEd@v4bel