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Re: [PATCH v1 07/15] xen/riscv: introduce tracking of pending vCPU interrupts, part 1
- To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 16 Jan 2026 15:42:44 +0100
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- Cc: Alistair Francis <alistair.francis@xxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Fri, 16 Jan 2026 14:43:03 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16.01.2026 15:25, Oleksii Kurochko wrote:
>
> On 1/7/26 5:28 PM, Jan Beulich wrote:
>>> +
>>> + /*
>>> + * VCPU interrupts
>>> + *
>>> + * We have a lockless approach for tracking pending VCPU interrupts
>>> + * implemented using atomic bitops. The irqs_pending bitmap represent
>>> + * pending interrupts whereas irqs_pending_mask represent bits changed
>>> + * in irqs_pending.
>> And hence a set immediately followed by an unset is then indistinguishable
>> from just an unset (or the other way around). This may not be a problem, but
>> if it isn't, I think this needs explaining.
>
> I am still not sure that this is actually a problem, or what kind of
> explanation
> is needed.
> |unset| is called only when the guest makes such a request, and the guest will
> make that request only after it has received an interrupt that was previously
> set in the|irq_pending| bitmap and then flushed to the hardware HVIP.
>
> If an interrupt is simply set and then unset without ever being flushed to the
> hardware HVIP, it seems there would be no issue, since it would not affect the
> guest. However, the question of why this happened at all would still remain.
>
> Do I miss some corner cases which should be taken into account?
> Should I still have to add some extra explanation to the comment or commit
> message?
Perhaps the problem is that really I can't see the full picture yet, for the
series not putting everything in place that is related.
Jan
|
