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

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Message-ID: <CANRm+CxjS_wEMLA6i81muQokKCWuba7pv8pua6qCt74nH8Tpjw@mail.gmail.com>
Date:   Tue, 18 Oct 2016 08:01:11 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.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()

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.

>  /*
>   * Make previous memory operations globally visible before
>   * sending the IPI through x2apic wrmsr. We need a serializing instruction or
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index edbbfc854e39..61cc6a5e3f44 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -319,7 +319,7 @@ static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
>          */
>         if (__test_and_clear_bit(KVM_PV_EOI_BIT, this_cpu_ptr(&kvm_apic_eoi)))
>                 return;
> -       apic_write(APIC_EOI, APIC_EOI_ACK);
> +       native_apic_msr_eoi_write(APIC_EOI, APIC_EOI_ACK);
>  }

If -cpu host,-x2apic we should go through mmio when writes xapic EOI.

Regards,
Wanpeng Li