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List:       xen-devel
Subject:    Re: [Xen-devel] APIC initialization when config file has "apic=0".
From:       Keir Fraser <keir () xensource ! com>
Date:       2007-03-29 17:52:21
Message-ID: C231BB65.C8BB%keir () xensource ! com
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On 29/3/07 18:13, "Petersson, Mats" <Mats.Petersson@amd.com> wrote:

> To me, if config file has "apic=0", the APIC should not stop the guest
> from being able to use the 8259 as an interrupt source. But this appears
> to be the case - and as far as I can see, it's because the APIC mode is
> not initialized (correctly/at all) when the guest is started.
> 
> Shouldn't "apic=0" mean that the guest appears like there's no APIC? In
> which case, this should mean that the IA32_APIC_BASE MSR should have the
> APIC disable bit set.

apic=0 simply means we don't advertise the APIC in the BIOS tables. It's
always physically present, and enabled by default. Its configuration is
identical to what you would get from a real physical processor at power on.

Bear in mind that platform features such as 'virtual wire' mode are usually
set up by the BIOS, which you are entirely circumventing by replacing
hvmloader. You can get around this particular problem by copying hvmloader's
apic_setup() function. If you want PCI functionality you may also want
pci_setup().

 -- Keir


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