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

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Date:	Wed, 17 Feb 2016 17:19:52 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	"Luis R. Rodriguez" <mcgrof@...nel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Andy Lutomirski <luto@...capital.net>,
	Juergen Gross <jgross@...e.com>,
	Michael Brown <mcb30@...e.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Joerg Roedel <joro@...tes.org>,
	Robert Moore <robert.moore@...el.com>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jan Beulich <JBeulich@...e.com>, Lv Zheng <lv.zheng@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	long.wanglong@...wei.com, Fengguang Wu <fengguang.wu@...el.com>,
	qiuxishi@...wei.com, Andrey Ryabinin <ryabinin.a.a@...il.com>,
	david.e.box@...el.com, X86 ML <x86@...nel.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v2 3/3] paravirt: rename paravirt_enabled to
 paravirt_legacy

On 02/17/2016 05:03 PM, Borislav Petkov wrote:
> On Wed, Feb 17, 2016 at 04:21:56PM -0500, Boris Ostrovsky wrote:
>> That's exactly the point: if something is mapped it's an error for a
>> non-PV kernel.
> How would something be mapped there? __PAGE_OFFSET is
> 0xffff880000000000.
>
> Or are you thinking about some insanely b0rked kernel code mapping stuff
> in there?

The latter. This is to detect things that clearly shouldn't be happening.

>
>> By removing paravirt_enabled() we may miss those errors. Worse, I think we
>> may even crash while doing pagetable walk (although it's probably better to
>> crash here than to use an unexpected translation in real code somewhere)
> Well, if this is the only site which keeps paravirt_enabled() from being
> buried, we need to think about a better way to detect a hypervisor.
> Maybe we should look at x86_hyper, use CPUID(0x4...)

Can't use CPUID 0x40000000 because it will return hypervisor (Xen or 
otherwise) for non-PV guests as well. In Xen's case, you can't determine 
guest type from hypervisor leaves.


> or something else.

We could say xen_pv_domain(). But this means using Xen-specific code in 
x86-generic file to detect things specified by ABI. I don't know if I'd 
like that.

-boris

>
> What's your preference?
>