linux-kernel - Re: [Xen-devel] [PATCH v2 3/3] paravirt: rename paravirt_enabled to paravirt

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Date:	Mon, 8 Feb 2016 16:32:40 +0000
From:	Andrew Cooper <andrew.cooper3@...rix.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Borislav Petkov <bp@...en8.de>
CC:	X86 ML <x86@...nel.org>, <david.e.box@...el.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Lv Zheng <lv.zheng@...el.com>, Jan Beulich <JBeulich@...e.com>,
	"H. Peter Anvin" <hpa@...or.com>, <qiuxishi@...wei.com>,
	<cocci@...teme.lip6.fr>, Xen Devel <xen-devel@...ts.xensource.com>,
	"Joerg Roedel" <joro@...tes.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Robert Moore <robert.moore@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	"Andrey Ryabinin" <aryabinin@...tuozzo.com>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	"Rusty Russell" <rusty@...tcorp.com.au>,
	Thomas Gleixner <tglx@...utronix.de>, <mcb30@...e.org>,
	Juergen Gross <jgross@...e.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Andy Lutomirski" <luto@...capital.net>,
	"Luis R. Rodriguez" <mcgrof@...nel.org>,
	<long.wanglong@...wei.com>, Fengguang Wu <fengguang.wu@...el.com>
Subject: Re: [Xen-devel] [PATCH v2 3/3] paravirt: rename paravirt_enabled to
 paravirt_legacy

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