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Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp |
Date: |
Tue, 07 Apr 2015 15:18:02 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 |
On 07/04/2015 13:57, Andreas Färber wrote:
>> > If this is some issue with sync'ing state back and forth before QEMU and
>> > KVM then the real issue has not been explained.
> Hm, hw/intc/apic_common.c:apic_reset_common() has:
>
> bsp = cpu_is_bsp(s->cpu);
> s->apicbase = APIC_DEFAULT_ADDRESS |
> (bsp ? MSR_IA32_APICBASE_BSP : 0) | MSR_IA32_APICBASE_ENABLE;
>
> What this is doing is really:
>
> bsp = cpu_get_apic_base(s->cpu->apic_state) & MSR_IA32_APICBASE_BSP;
> s->apicbase = APIC_DEFAULT_ADDRESS |
> (bsp ? MSR_IA32_APICBASE_BSP : 0) | MSR_IA32_APICBASE_ENABLE;
>
> Unless I'm missing something, since we are in the APIC device's reset
> function, this is effectively a twisted way of writing:
>
> bsp = s->apicbase & MSR_IA32_APICBASE_BSP;
> s->apicbase = APIC_DEFAULT_ADDRESS |
> (bsp ? MSR_IA32_APICBASE_BSP : 0) | MSR_IA32_APICBASE_ENABLE;
Yes, this is more readable.
> In which case we already relied on s->cpu and could thus simply change
> this to something like:
>
> bsp = CPU(s->cpu)->cpu_index == 0;
> s->apicbase = APIC_DEFAULT_ADDRESS |
> (bsp ? MSR_IA32_APICBASE_BSP : 0) | MSR_IA32_APICBASE_ENABLE;
>
> Then the apicbase manipulation would be nicely encapsulated in the APIC
> rather than the APIC reset retaining it and the CPU reset meddling with
> its state.
... but I find this worse. apic_designate_bsp corresponds to hardware
executing the MP initialization protocol.
Paolo
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp, (continued)
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp, Paolo Bonzini, 2015/04/07
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp, Andreas Färber, 2015/04/07
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp, Paolo Bonzini, 2015/04/07
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp, Andreas Färber, 2015/04/07
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp, Andreas Färber, 2015/04/07
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp, Igor Mammedov, 2015/04/07
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp, Andreas Färber, 2015/04/07
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp, Paolo Bonzini, 2015/04/07
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp, Andreas Färber, 2015/04/07
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp, Paolo Bonzini, 2015/04/07
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp,
Paolo Bonzini <=
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp, Denis V. Lunev, 2015/04/07
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp, Paolo Bonzini, 2015/04/07
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp, Denis V. Lunev, 2015/04/07
- Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp, Andreas Färber, 2015/04/07