Re: [PATCH] x86/xen: fix warning when running with nosmt mitigations

[boris.ostrovsky@xxxxxxxxxx]

On 11/5/20 7:47 PM, Brian Masney wrote:
> On Thu, Nov 05, 2020 at 07:35:29PM -0500, Brian Masney wrote:
>> diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
>> index 799f4eba0a62..4a052459a08e 100644
>> --- a/arch/x86/xen/spinlock.c
>> +++ b/arch/x86/xen/spinlock.c
>> @@ -93,9 +93,24 @@ void xen_init_lock_cpu(int cpu)
>>  
>>  void xen_uninit_lock_cpu(int cpu)
>>  {
>> +    int irq;
>> +
>>      if (!xen_pvspin)
>>              return;
>>  
>> +    /*
>> +     * When booting the kernel with 'mitigations=auto,nosmt', the secondary
>> +     * CPUs are not activated and only the primary thread on each CPU core
>> +     * is used. In this situation, xen_hvm_smp_prepare_cpus(), and more
>> +     * importantly xen_init_lock_cpu(), is not called, so the
>> +     * lock_kicker_irq is not initialized for the secondary CPUs. Let's
>> +     * exit early if the irq is not set to avoid a warning in the console
>> +     * log.
>> +     */
>> +    irq = per_cpu(lock_kicker_irq, cpu);
>> +    if (irq == -1)
>> +            return;
>> +
>>      unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
> As soon as I saw this on lore, I saw that I should have passed the irq
> variable to unbind_from_irqhandler() rather than doing another per_cpu()
> lookup. I'll wait for feedback about the general approach before posting
> a v2.


This looks good. I'd shorten the comment though: your commit message already 
describes the scenario. And change the subject to something like "Don't unbind 
uninitialized lock_kicker_irq".


-boris