From mboxrd@z Thu Jan  1 00:00:00 1970
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH v2 3/3] paravirt: rename paravirt_enabled to
 paravirt_legacy
Date: Wed, 17 Feb 2016 17:39:23 -0500
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To: Andy Lutomirski <luto@amacapital.net>, Borislav Petkov <bp@alien8.de>
Cc: X86 ML <x86@kernel.org>, david.e.box@intel.com, Andrey Ryabinin <ryabinin.a.a@gmail.com>, Lv Zheng <lv.zheng@intel.com>, Jan Beulich <JBeulich@suse.com>, "H. Peter Anvin" <hpa@zytor.com>, qiuxishi@huawei.com, Mauro Carvalho Chehab <mchehab@osg.samsung.com>, Xen Devel <xen-devel@lists.xensource.com>, Joerg Roedel <joro@8bytes.org>, "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>, Robert Moore <robert.moore@intel.com>, Ingo Molnar <mingo@redhat.com>, Andrey Ryabinin <aryabinin@virtuozzo.com>, Rusty Russell <rusty@rustcorp.com.au>, Thomas Gleixner <tglx@linutronix.de>, Michael Brown <mcb30@ipxe.org>, Juergen Gross <jgross@suse.com>, Andrew Cooper <andrew.cooper3@citrix.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "Luis R. Rodriguez" <mcgrof@kernel.org>, David Vrabel <david.vrabel@citrix.com>, long.wanglong@huawei.com, Fengguang Wu <fengguang.wu@i>
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On 02/17/2016 05:18 PM, Andy Lutomirski wrote:
> On Wed, Feb 17, 2016 at 2:03 PM, Borislav Petkov <bp@alien8.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