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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 30 Nov 2012 09:01:50 -0800
Message-ID: <CA+55aFziiaWt1nU-EPKc=tFd0EvSm2iSBJ2MAqxNiWP5O0mv+w@mail.gmail.com>
Subject: Re: [PATCH 8/8] x86, cleanups: Simplify sync_core() in the case of no CPUID
To: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
        Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Mario Gzuk <mariogzuk@technikz.de>
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On Thu, Nov 29, 2012 at 1:24 PM, H. Peter Anvin <hpa@linux.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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