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Subject: Re: [RFC 05/10] x86/speculation: Add basic IBRS support
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To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        David Woodhouse <dwmw2@infradead.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
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        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>,
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        Tim Chen <tim.c.chen@linux.intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>, kvm@vger.kernel.org,
        x86@kernel.org
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From:   Arjan van de Ven <arjan@linux.intel.com>
Message-ID: <68fc14f7-38b0-5127-5c7a-a11c27e3b166@linux.intel.com>
Date:   Wed, 24 Jan 2018 07:09:06 -0800
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On 1/24/2018 1:10 AM, Greg Kroah-Hartman wrote:
> 
>> That means the whitelist ends up basically empty right now. Should I
>> add a command line parameter to override it? Otherwise we end up having
>> to rebuild the kernel every time there's a microcode release which
>> covers a new CPU SKU (which is why I kind of hate the whitelist, but
>> Arjan is very insistent...)
> 
> Ick, no, whitelists are a pain for everyone involved.  Don't do that
> unless it is absolutely the only way it will ever work.
> 
> 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 their own numbers)
and as a result there might be several numbers that have those issues with their IBRS for the same F/M/S