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From: Tvrtko Ursulin <tvrtko.ursulin@sophos.com>
Organization: Sophos Plc
To: "Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: 2.6.35 hangs on early boot in KVM
Date: Wed, 4 Aug 2010 11:46:55 +0100
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CC: Gleb Natapov <gleb@redhat.com>, Yinghai Lu <yinghai@kernel.org>,
        Avi Kivity <avi@redhat.com>,
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        KVM list <kvm@vger.kernel.org>
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On Wednesday 04 Aug 2010 11:37:43 Eric W. Biederman wrote:
> Gleb Natapov <gleb@redhat.com> writes:
> > On Wed, Aug 04, 2010 at 10:16:08AM +0100, Tvrtko Ursulin wrote:
> >> Not the tip but 2.6.35 with earlyprintk=ttyS0,115200:
> >>
> >> [    0.000000] Processor #0 (Bootup-CPU)
> >> [    0.000000] I/O APIC #1 Version 17 at 0xFEC00000.
> >> [    0.000000] BUG: unable to handle kernel paging request at ffffb030
> >> [    0.000000] IP: [<c011d136>] native_apic_mem_read+0x16/0x20
> >> [    0.000000] *pde = 00832067 *pte = 00000000
> >
> > Accessing APIC version register before APIC is mapped.
>
> Yep. I see it now.  We have some of the silliest code.  We only
> go down this path for certain revs of Intel cpus, and I double checked
> this change on an AMD cpu which explains why I missed hitting this
> case.
>
> The call path that is new in they bisected commit is:
> MP_ioapic_info()
>   mp_register_ioapic()
>    io_apic_unique_id()
>      io_apic_get_unique_id()
>        get_physical_broadcast()
>          modern_apic()
>            lapic_get_version()
>              apic_read(APIC_LVR)
>
>
> Tvrtko can you test this patch and verify it fixes the kvm booting
> issue?
>
> This patch just maps the lapic early in the mmparse.c just like we
> do in acpi/boot.c when parsing the acpi tables.

Boots fine, thanks!

Tvrtko

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