Date: Tue, 30 Jan 2018 07:56:53 +0100 From: Ingo Molnar <mingo@...nel.org> To: Dan Williams <dan.j.williams@...el.com> Cc: Thomas Gleixner <tglx@...utronix.de>, linux-arch <linux-arch@...r.kernel.org>, Tom Lendacky <thomas.lendacky@....com>, Andi Kleen <ak@...ux.intel.com>, Kees Cook <keescook@...omium.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, Greg KH <gregkh@...uxfoundation.org>, X86 ML <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>, Al Viro <viro@...iv.linux.org.uk>, "H. Peter Anvin" <hpa@...or.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Alan Cox <alan@...ux.intel.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v5 04/12] x86: introduce __uaccess_begin_nospec and ifence * Dan Williams <dan.j.williams@...el.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
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