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To:     Tim Chen <tim.c.chen@linux.intel.com>,
        Jiri Kosina <jikos@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>
Cc:     Tom Lendacky <thomas.lendacky@amd.com>,
        Ingo Molnar <mingo@redhat.com>,
        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>,
        Dave Hansen <dave.hansen@intel.com>,
        Casey Schaufler <casey.schaufler@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        linux-kernel@vger.kernel.org, x86@kernel.org
References: <cover.1537392876.git.tim.c.chen@linux.intel.com>
 <0c55c162a077aadbfd57878e2694e35292c1a29c.1537392876.git.tim.c.chen@linux.intel.com>
From:   Jon Masters <jcm@redhat.com>
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Subject: Re: [PATCH 2/2] x86/speculation: Provide application property based
 STIBP protection
Message-ID: <1a501628-a232-a126-166e-814c26243f2d@redhat.com>
Date:   Tue, 2 Oct 2018 11:41:28 -0400
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On 9/19/18 5:35 PM, Tim Chen wrote:
> This patch provides an application property based spectre_v2
> protection with STIBP against attack from another app from
> a sibling hyper-thread.  For security sensitive non-dumpable
> app, STIBP will be turned on before switching to it for Intel
> processors vulnerable to spectre_v2.

A general comment. I think in practice this will be similar to the
speculative store buffer bypass (aka "variant 4") issue in terms of
opt-in mitigation. Many users won't want to take the performance hit of
having STIBP by default for peer threads. We should make sure that we
don't force users into a mitigation but retain an option. Whether it's
default-on or not can be debated, though I think the vendors lean toward
having default-off with an opt-in, and customers will probably agree. So
anyway, I encourage a pragmatic approach similar to that for SSBD.

Jon.

-- 
Computer Architect | Sent with my Fedora powered laptop