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

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Message-ID: <56C4F69B.4020705@oracle.com>
Date:	Wed, 17 Feb 2016 17:39:23 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Andy Lutomirski <luto@...capital.net>,
	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>,
	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 05:18 PM, Andy Lutomirski wrote:
> On Wed, Feb 17, 2016 at 2:03 PM, Borislav Petkov <bp@...en8.de> 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?
>>
>>> 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...) or something else.
>>
>> What's your preference?
> I'm confused.  Isn't it the other way around?  That is, checking for
> the hypervisor range on all systems should be safer, right?  Or am I
> missing something?

Hmm. I think you are right --- I was following wrong branch of the 'if' 
statement. We are always going straight to note_page().

Then yes, we should be able to remove paravirt_enabled(). Sorry for the 
noise.

-boris