linux-kernel - Re: [PATCH 8/8] x86, cleanups: Simplify sync

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Message-ID: <CA+55aFziiaWt1nU-EPKc=tFd0EvSm2iSBJ2MAqxNiWP5O0mv+w@mail.gmail.com>
Date:	Fri, 30 Nov 2012 09:01:50 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
Cc:	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mario Gzuk <mariogzuk@...hnikz.de>
Subject: Re: [PATCH 8/8] x86, cleanups: Simplify sync_core() in the case of no CPUID

On Thu, Nov 29, 2012 at 1:24 PM, H. Peter Anvin <hpa@...ux.intel.com> wrote:
>
> Thinking about it some more, there is another reason to not do this,
> which is that we don't want this particular CPUID to be paravirtualized;
> we're after the synchronizing side effect, not the CPUID return value
> itself.
>
> So let's leave it as a primitive; it gets too confusing otherwise.

Hmm. The virtualization issue brings up another point: do we *really*
want to use cpuid for serialization at all?

Exactly because under _real_ virtualization (as opposed to para-virt),
it can cause unnecessary exits in a virtualized environment, no?

So I'm wondering if there is any better synchronizing instruction..

I guess sync_core() isn't used *that* much, so maybe we don't care,
but I thought I'd ask...

                Linus
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