From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tim Chen <tim.c.chen@linux.intel.com>
Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict
 Indirect Branch Speculation
Date: Tue, 23 Jan 2018 16:47:36 -0800
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Cc: Andy Lutomirski <luto@amacapital.net>,
        KarimAllah Ahmed <karahmed@amazon.de>,
        linux-kernel@vger.kernel.org,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Borislav Petkov <bp@suse.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "H . Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>,
        Joerg Roedel <joro@8bytes.org>,
        Jun Nakajima <jun.nakajima@intel.com>,
        Laura Abbott <labbott@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Masami Hiramatsu <mh
To: "Woodhouse, David" <dwmw@amazon.co.uk>,
        Andi Kleen <ak@linux.intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>
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On 01/23/2018 03:14 PM, Woodhouse, David wrote:
> On Tue, 2018-01-23 at 14:49 -0800, Andi Kleen wrote:
>>> Not sure.  Maybe to start, the answer might be to allow it to be set for
>>> the ultra-paranoid, but in general don't enable it by default.  Having it
>>> enabled would be an alternative to someone deciding to disable SMT, since
>>> that would have even more of a performance impact.
>>
>> I agree. A reasonable strategy would be to only enable it for
>> processes that have dumpable disabled. This should be already set for
>> high value processes like GPG, and allows others to opt-in if
>> they need to.
> 
> That seems to make sense, and I think was the solution we were
> approaching for IBPB on context switch too, right?
> 
> Are we generally agreed on dumpable as the criterion for both of those?
> 

It is a reasonable approach.  Let a process who needs max security
opt in with disabled dumpable. It can have a flush with IBPB clear before
starting to run, and have STIBP set while running.

Tim