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Date: Tue, 23 Jan 2018 14:49:56 -0800
From: Andi Kleen <ak@linux.intel.com>
To: Tom Lendacky <thomas.lendacky@amd.com>
Cc: "Woodhouse, David" <dwmw@amazon.co.uk>,
	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 <mhiramat@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tim Chen <tim.c.chen@linux.intel.com>, kvm@vger.kernel.org,
	x86@kernel.org, Arjan Van De Ven <arjan.van.de.ven@intel.com>
Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict
 Indirect Branch Speculation
Message-ID: <20180123224956.GQ7844@tassilo.jf.intel.com>
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> 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.

-Andi