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

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Date:	Mon, 8 Feb 2016 11:31:04 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Andrew Cooper <andrew.cooper3@...rix.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 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().

-boris