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Subject: Re: [Xen-devel] [PATCH v2 3/3] paravirt: rename paravirt_enabled to
 paravirt_legacy
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Borislav Petkov <bp@alien8.de>
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From: Andrew Cooper <andrew.cooper3@citrix.com>
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Date: Mon, 8 Feb 2016 16:32:40 +0000
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On 08/02/16 16:31, Boris Ostrovsky wrote:
>
>
> On 02/08/2016 11:26 AM, Andrew Cooper wrote:
>> On 08/02/16 16:12, Boris Ostrovsky wrote:
>>>
>>> On 02/08/2016 11:05 AM, Andrew Cooper wrote:
>>>> For compatibility with other virtualisation specs, Xen's cpuid leaves
>>>> shift depending on configuration.
>>>>
>>>> Spec at
>>>> http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/include/public/arch-x86/cpuid.h;h=d709340f18d089560b959835eabb7b6609542c7e;hb=HEAD#l33
>>>>
>>>>
>>>>
>>>> Basically, they are either at 0x40000000, or 0x40000100 if viridian or
>>>> vmware compatibility has been enabled.
>>> (Also in arch/x86/include/asm/xen/cpuid.h in Linux tree).
>> The other complication is that, for a PV guest, you must use the forced
>> emulation prefix for the cpuid instruction to trap into the hypervisor.
>>
>> This either means you must be sure you are under Xen to start with, or
>> use an extable entry to catch the #UD fault if you are not under Xen.
>
> I think we are OK for PV because this code will be executed after
> pvops are set and so we will be calling xen_cpuid().

Great.

~Andrew