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Date:   Wed, 9 Jan 2019 10:41:47 -0800
From:   Tony Luck <>
To:     Borislav Petkov <>
Cc:     Vitaly Kuznetsov <>,
        Reinette Chatre <>,
        Babu Moger <>, X86-ML <>,
        Linux Kernel Mailing List <>,
        Fenghua Yu <>,
        Thomas Gleixner <>,
        Ingo Molnar <>,
        "H. Peter Anvin" <>,
        Jan H. Schönherr <>,
        David Duncan <>
Subject: Re: [PATCH] x86/intel_rdt: use rdmsr_safe() to workaround AWS host issue

On Wed, Jan 9, 2019 at 5:00 AM Borislav Petkov <> wrote:
> On Wed, Jan 09, 2019 at 01:09:31PM +0100, Vitaly Kuznetsov wrote:
> > Hm, why is that? In theory, hypervisors can pass through or emulate the
> > required MSRs...
> ...and when the theory becomes reality we'll remove the check.

In practice that may be a long time coming. We don't have many CLOSIDs, or
bits in a cache mask, at the h/w level. If you start trying to
subdivide those resources
to pass a subset to a guest, then you'll quickly find that you have no
flexibility in the
guest to do anything useful.  It would only work if you limited to
two, or perhaps three


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