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Subject: Re: [PATCH] x86/xen: fix warning when running with nosmt mitigations
To:     Brian Masney <bmasney@redhat.com>, jgross@suse.com,
        sstabellini@kernel.org
Cc:     tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org,
        hpa@zytor.com, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org, dustymabe@redhat.com
References: <20201106003529.391649-1-bmasney@redhat.com>
 <20201106004743.GA380136@tp-x1>
From:   boris.ostrovsky@oracle.com
Organization: Oracle Corporation
Message-ID: <a541a64b-aabc-bb62-4cf7-da5004a756d7@oracle.com>
Date:   Fri, 6 Nov 2020 19:44:16 -0500
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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