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Re: [PATCH v2] x86/apic: Avoid infinite loop in io_apic_level_ack_pending()
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Jason Andryuk <jason.andryuk@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 15 Oct 2025 14:59:39 +0200
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Delivery-date: Wed, 15 Oct 2025 12:59:46 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 14.10.2025 09:37, Roger Pau Monné wrote:
> On Mon, Oct 13, 2025 at 05:11:06PM -0400, Jason Andryuk wrote:
>> io_apic_level_ack_pending() will end up in an infinite loop if
>> entry->pin == -1. entry does not change, so it will keep reading -1.
>
> Do you know how you end up with an entry with pin == -1 on the
> irq_pin_list? Are there systems with gaps in the GSI space between
> IO-APICs? So far everything I saw had the IO-APIC in contiguous GSI
> space.
>
>> Convert to a proper for loop so that continue works. Add a new helper,
>> next_entry(), to handle advancing to the next irq_pin_list entry.
>>
>> Fixes: f821102450a1 ("x86: IRQ Migration logic enhancement.")
>> Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
>> ---
>> v2:
>> continue (not break) for pin == -1.
>>
>> I added the next_entry() helper since putting the expression in the for
>> loop is a little cluttered. The helper can also be re-used for other
>> instances within the file.
Would this intention ...
>> --- a/xen/arch/x86/io_apic.c
>> +++ b/xen/arch/x86/io_apic.c
>> @@ -1586,14 +1586,21 @@ static int __init cf_check setup_ioapic_ack(const
>> char *s)
>> }
>> custom_param("ioapic_ack", setup_ioapic_ack);
>>
>> +static struct irq_pin_list *next_entry(struct irq_pin_list *entry)
>
> I think you can make the entry parameter const?
... possibly conflict with such a change?
Jan
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