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

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Message-ID: <20160208164545.GJ28980@pd.tnic>
Date:	Mon, 8 Feb 2016 17:45:45 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Andrew Cooper <andrew.cooper3@...rix.com>
Cc:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	X86 ML <x86@...nel.org>, david.e.box@...el.com,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Lv Zheng <lv.zheng@...el.com>, Jan Beulich <JBeulich@...e.com>,
	"H. Peter Anvin" <hpa@...or.com>, qiuxishi@...wei.com,
	cocci@...teme.lip6.fr, Xen Devel <xen-devel@...ts.xensource.com>,
	Joerg Roedel <joro@...tes.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Robert Moore <robert.moore@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Thomas Gleixner <tglx@...utronix.de>, mcb30@...e.org,
	Juergen Gross <jgross@...e.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	"Luis R. Rodriguez" <mcgrof@...nel.org>, long.wanglong@...wei.com,
	Fengguang Wu <fengguang.wu@...el.com>
Subject: Re: [Xen-devel] [PATCH v2 3/3] paravirt: rename paravirt_enabled to
 paravirt_legacy

On Mon, Feb 08, 2016 at 04:38:40PM +0000, Andrew Cooper wrote:
> Does the early loader have extable support?  If so, this is fairly easy
> to fix.  If not, we have a problem.

It doesn't and regardless, you want to have this CPUID querying as
simple as possible. No special handling, no special prefixes as it
should be able to run on other hypervisors too.

If one can't execute a simple CPUID(0x4...) on a xen guest and get the
results back, then for early, we will have to do what we've done until
now and simply emulate the MSR accesses.

Later code can use then xen_cpuid() and all is fine. We should still get
rid of paravirt_enabled() though.

-- 
Regards/Gruss,
    Boris.

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