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Re: [PATCH] x86/HVM: don't mark evtchn upcall vector as pending when vLAPIC is disabled
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Thu, 24 Nov 2022 10:06:06 +0100
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- Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Paul Durrant <paul@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
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On Thu, Nov 24, 2022 at 09:42:40AM +0100, Roger Pau Monné wrote:
> On Thu, Nov 24, 2022 at 08:59:00AM +0100, Jan Beulich wrote:
> > - problematic wrt evtchn_upcall_pending, once set, preventing event
> > injection later on.
> > As you may have inferred already, I'm inclined to suggest to drop the
> > the is_vcpu_online() check from hvm_set_callback_via().
> >
> > One related question here is whether vlapic_do_init() shouldn't have
> > the non-architectural side effect of clearing evtchn_upcall_pending.
> > While this again violates the principle of the hypervisor only ever
> > setting that bit, it would deal with the risk of no further event
> > injection once the flag is set, considering that vlapic_do_init()
> > clears IRR (and ISR).
>
> That would seem sensible to me, and was kind of what I was suggesting
> in:
>
> https://lore.kernel.org/xen-devel/Y3eO0bMKRPYJc2yQ@Air-de-Roger/
Another option would be for vcpu_mark_events_pending() to
unconditionally call hvm_assert_evtchn_irq() regardless of the state
of evtchn_upcall_pending. This will create some spurious events.
Regards, Roger.
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