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

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Date:	Mon, 8 Feb 2016 16:55:07 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	"Luis R. Rodriguez" <mcgrof@...nel.org>, cocci@...teme.lip6.fr,
	Juergen Gross <jgross@...e.com>, 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>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.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 Mon, Feb 08, 2016 at 10:39:43AM -0500, Boris Ostrovsky wrote:
> It does. Very much IIRC, the problem was not caused by an access to MSR but
> rather some sort of address not being available somewhere.

See below.

> >- microcode application on Xen: we've had this before. The hypervisor
> >should do that (if it doesn't do so already).
> 
> it does.

Good.

> >So yes, that paravirt_enabled() thing should go away. Even more so if we
> >have CPUID leaf 0x4... reserved for hypervisors.
> 
> I actually think this was the original proposal until we realized we had
> paravirt_enabled(). So we can go back to checking CPUID 0x40000000.
> 
> We might also be able to test for (x86_hyper!=NULL) and have guests that do
> microcode management prior to init_hypervisor() rely on hypervisors ignoring
> MSR accesses (as they do today).

Right, so the early loader can't do that as on 32-bit it runs even
before paging has been enabled. So I *think* the thing with CPUID would
be best. What does the xen hypervisor return in regs when I do CPUID(4)?
I.e., how do I reliably detect it in the guest?

I can whip up a quick patch and get rid of paravirt_enabled() while at
it...

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.