linux-kernel - Re: [PATCH 0/7] IBRS patch series

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Message-ID: <1515095164.29312.32.camel@infradead.org>
Date:   Thu, 04 Jan 2018 19:46:04 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Andrew Cooper <andrew.cooper3@...rix.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/7] IBRS patch series

On Thu, 2018-01-04 at 19:40 +0000, Andrew Cooper wrote:
> 
> Also remember that sibling threads share a BTB, so you can't rely on
> isolated straight-line codepath on the current cpu for safety. (e.g. by
> issuing an IBPB on every entry to supervisor mode).

That is just one of a whole litany of reasons the RSB gets flushed,
*many* of which were individually sufficient for us to throw our toys
out of the pram and say "OK, this doesn't work on Skylake".

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