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 17:19:52 -0500
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To: 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>, Andy Lutomirski <luto@amacapital.net>, "Luis R. Rodriguez" <mcgrof@kernel.org>, David Vrabel <david.vrabel@citrix.com>, long.wanglong@h
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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?
>