linux-kernel - Re: [PATCH] x86/smp: Add irq_enter/exit() in smp_reschedule

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Date:   Wed, 19 Oct 2016 16:10:54 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86/smp: Add irq_enter/exit() in
 smp_reschedule_interrupt()



On 19/10/2016 16:01, Wanpeng Li wrote:
> 2016-10-18 8:01 GMT+08:00 Wanpeng Li <kernellwp@...il.com>:
>> 2016-10-17 18:08 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
>> [...]
>>>>> Something like the below avoids all that. Paravirt will still need fixing.
>>>>
>>>> kvm_guest_apic_eoi_write
>>>>  -> native_apic_msr_write
>>>
>>> kvm_guest_apic_eoi_write can use native_apic_msr_eoi_write too:
>>>
>>> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
>>> index f5aaf6c83222..9769d76a62c4 100644
>>> --- a/arch/x86/include/asm/apic.h
>>> +++ b/arch/x86/include/asm/apic.h
>>> @@ -174,7 +174,7 @@ static inline void disable_local_APIC(void) { }
>>>  static inline void lapic_update_tsc_freq(void) { }
>>>  #endif /* !CONFIG_X86_LOCAL_APIC */
>>>
>>> -#ifdef CONFIG_X86_X2APIC
>>> +#if defined CONFIG_X86_X2APIC || defined CONFIG_KVM_GUEST
>>
>> If CONFIG_X86_X2APIC is undefined and CONFIG_KVM_GUEST is defined,
>> there are undefined reference warning for x2apic_mode and check_x2apic
>> etc since they are extern variables and just define under
>> CONFIG_X86_X2APIC.
> 
> [...]
> 
>>
>> If -cpu host,-x2apic we should go through mmio when writes xapic EOI.
> 
> Any ideas? :)

Make apic_set_eoi_write return the old pointer?

Paolo