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Date:   Mon, 19 Nov 2018 13:49:45 +0100 (CET)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Tim Chen <tim.c.chen@linux.intel.com>
cc:     Jiri Kosina <jikos@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Andi Kleen <ak@linux.intel.com>,
        Casey Schaufler <casey.schaufler@intel.com>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        stable@vger.kernel.org
Subject: Re: STIBP by default.. Revert?
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On Sun, 18 Nov 2018, Tim Chen wrote:
> On 11/18/2018 02:17 PM, Jiri Kosina wrote:
> > On Sun, 18 Nov 2018, Linus Torvalds wrote:
> > 
> >>> So, I think it's as theoretical as any other spectrev2 (only with the
> >>> extra "HT" condition added on top).
> >>
> >> What? No.
> >>
> >> It's *way* more theoretical than something like meltdown, which could
> >> be trivially used to get data from another protection domain.
> > 
> > Oh yeah, I absolutely agree that spectrev2 and Meltdown and completely 
> > different beasts.
> > 
> >> Have you seen any actual realistic attacks for normal human users?
> >> Things where the *kernel* should actually care?
> >>
> >> The javascript thing is for the browser to fix up, 
> > 
> > It's probably not just browsers, but anything running JITed sandboxed 
> > code. So the most straightforward way might be the prctl() aproach, where 
> > userspace would claim "I do care about this, please fix it up for me". So 
> > prctl() + perhaps SECCOMP.
> > 
> > Which gets us back to Tim's fixup patch. Do you still prefer the revert, 
> > given the existence of that? I think that if Tim's fixup makes it through 
> > (it's currently missing SECCOMP handling, but that is trivial to add on 
> > top), it might be the best compromise. We'd also have have to make IBPB 
> > obey it to be consistent (and get even a few more % of performance back), 
> > but that's easy as well.
> > 
> I think if Thomas can merge my patchset along with Jiri's, the default
> option will become opt in for tasks that want the extra security and we
> won't lose performance.

If it would be in mergeable state ....

Thanks,

	tglx