netdev - RE: [PATCH 06/18] x86, barrier: stop speculation for failed access

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Date:   Mon, 8 Jan 2018 12:00:28 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Linus Torvalds' <torvalds@...ux-foundation.org>,
        Willy Tarreau <w@....eu>
CC:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Dan Williams <dan.j.williams@...el.com>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Network Development" <netdev@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: RE: [PATCH 06/18] x86, barrier: stop speculation for failed access_ok

From: Linus Torvalds
> Sent: 07 January 2018 19:47
...
> Also, people definitely *are* noticing the performance issues with the
> current set of patches, and they are causing real problems. Go search
> for reports of Amazon AWS slowdowns.

Try over 35% slowdown....
Given that AWS instance runs known code (user and kernel) why do we
need to worry about any of these sideband attacks?

	David