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Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
Date: Tue, 30 Jan 2018 07:56:53 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	linux-arch <linux-arch@vger.kernel.org>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Andi Kleen <ak@linux.intel.com>, Kees Cook <keescook@chromium.org>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	Greg KH <gregkh@linuxfoundation.org>, X86 ML <x86@kernel.org>,
	Ingo Molnar <mingo@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Alan Cox <alan@linux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v5 04/12] x86: introduce __uaccess_begin_nospec and ifence
Message-ID: <20180130065653.gsp7blb3jttd6e6t@gmail.com>
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* Dan Williams <dan.j.williams@intel.com> wrote:

> > The flip side is that if the MFENCE stalls the STAC that is ahead of it could be
> > processed for 'free' - while it's always post barrier with my suggestion.
> 
> This 'for free' aspect is what I aiming for.

Ok.

> >
> > But in any case it would be nice to see a discussion of this aspect in the
> > changelog, even if the patch does not change.
> 
> I'll add a note to the changelog that having the fence after the
> 'stac' hopefully allows some overlap of the cost of 'stac' and the
> flushing of the instruction pipeline.

Perfect!

Thanks,

	Ingo