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

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Message-ID: <b2318cab-2c58-b84c-7d77-3fe1d1878e0d@redhat.com>
Date:   Mon, 24 Oct 2016 16:32:19 +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>,
        Radim Krcmar <rkrcmar@...hat.com>
Subject: Re: [PATCH] x86/smp: Add irq_enter/exit() in
 smp_reschedule_interrupt()



On 19/10/2016 16:30, Wanpeng Li wrote:
> Cc Radim,
> 2016-10-19 22:10 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
>>
>>
>> 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.
>>>
> 
> This results in undefined reference warning.
> 
>>>
>>>>
>>>> If -cpu host,-x2apic we should go through mmio when writes xapic EOI.
>>>
>>> Any ideas? :)
>>
>> Make apic_set_eoi_write return the old pointer?
> 
> Could you elaborate? :)

No, that won't work due to how struct apic works and how
apic_set_eoi_write patches it.  One possibility then is to add a

        void (*native_eoi_write)(u32 reg, u32 v);

field to struct apic, and make apic_set_eoi_write set

	(*drv)->native_eoi_write = (*drv)->eoi_write;
	(*drv)->eoi_write = eoi_write;

Then kvm.c can call

	apic->native_eoi_write(reg, v);

Thanks,

Paolo