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Message-ID: <1516807081.13558.147.camel@infradead.org>
Subject: Re: [RFC 05/10] x86/speculation: Add basic IBRS support
 infrastructure
From:   David Woodhouse <dwmw2@infradead.org>
To:     Arjan van de Ven <arjan@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        KarimAllah Ahmed <karahmed@amazon.de>,
        linux-kernel@vger.kernel.org, Andi Kleen <ak@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andy Lutomirski <luto@kernel.org>,
        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>,
        "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>,
        Radim =?UTF-8?Q?Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@redhat.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>, kvm@vger.kernel.org,
        x86@kernel.org
In-Reply-To: <68fc14f7-38b0-5127-5c7a-a11c27e3b166@linux.intel.com>
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Date:   Wed, 24 Jan 2018 15:18:01 +0000
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On Wed, 2018-01-24 at 07:09 -0800, Arjan van de Ven wrote:
> On 1/24/2018 1:10 AM, Greg Kroah-Hartman wrote:
> > Arjan, why do you think this can only be done as a whitelist?
>
> I suggested a minimum version list for those cpus that need it.
>
> microcode versions are tricky (and we've released betas etc etc with thei=
r own numbers)
> and as a result there might be several numbers that have those issues wit=
h their IBRS for the same F/M/S

I really think that's fine. Anyone who uses beta microcodes, should be
perfectly prepared to deal with the results. And probably *wanted* to
be able to actually test them, instead of having the kernel refuse to
do so.

So if there are beta microcodes floating around with numbers higher
than in Intel's currently-published list, which are not yet known to be
safe (or even if they're known not to be), that's absolutely OK.

If you're telling me that there will be *publicly* released microcodes
with version numbers higher than those in the list, which still have
the same issues... well, then I think Mr Shouty is going to come for
another visit.
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