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Subject: Re: [PATCH linux v3 3/9] xen: introduce xen_vcpu_id mapping
To: Julien Grall <julien.grall@arm.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>, xen-devel@lists.xenproject.org
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 <258e8e2e-29c4-1a88-2271-581f2ea59ec2@arm.com>
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From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Date: Sun, 4 Sep 2016 17:12:18 -0400
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On 09/02/2016 11:29 AM, Julien Grall wrote:
>
>> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
>> index 0f87db2..c833912 100644
>> --- a/arch/x86/xen/enlighten.c
>> +++ b/arch/x86/xen/enlighten.c
>> @@ -1795,6 +1806,12 @@ static void __init init_hvm_pv_info(void)
>>
>>      xen_setup_features();
>>
>> +    cpuid(base + 4, &eax, &ebx, &ecx, &edx);
>> +    if (eax & XEN_HVM_CPUID_VCPU_ID_PRESENT)
>> +        this_cpu_write(xen_vcpu_id, ebx);
>> +    else
>> +        this_cpu_write(xen_vcpu_id, smp_processor_id());
>> +
>>      pv_info.name = "Xen HVM";
>>
>>      xen_domain_type = XEN_HVM_DOMAIN;
>> @@ -1806,6 +1823,10 @@ static int xen_hvm_cpu_notify(struct
>> notifier_block *self, unsigned long action,
>>      int cpu = (long)hcpu;
>>      switch (action) {
>>      case CPU_UP_PREPARE:
>> +        if (cpu_acpi_id(cpu) != U32_MAX)
>> +            per_cpu(xen_vcpu_id, cpu) = cpu_acpi_id(cpu);
>> +        else
>> +            per_cpu(xen_vcpu_id, cpu) = cpu;
>
> I have not tried myself. But looking at the code, the notifiers
> xen_hvm_cpu_notifier and evtchn_fifo_cpu_notifier have the same
> priority. So what does prevent the code above to be executed after the
> event channel callback?


We will be converting to new hotplug state machine where this order will
be guaranteed:

 https://lists.xenproject.org/archives/html/xen-devel/2016-08/msg01914.html


-boris