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Date: Fri, 29 Aug 2014 08:36:47 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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To: Andy Lutomirski <luto@amacapital.net>
CC: Gleb Natapov <gleb@kernel.org>,
        Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        "Theodore Ts'o" <tytso@mit.edu>, Kees Cook <keescook@chromium.org>,
        kvm list <kvm@vger.kernel.org>,
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        Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Alok Kataria <akataria@vmware.com>
Subject: Re: GET_RNG_SEED hypercall ABI? (Re: [PATCH v5 0/5] random,x86,kvm:
 Rework arch RNG seeds and get some from kvm)
References: <CALCETrV5U61C-gkikZtddd5RtZWFVRpkjVk69B+ymvy=xauLaQ@mail.gmail.com> <20140828141704.GI18167@minantech.com> <CALCETrXDygWbKwPNux=qEbqVCCk28Lu7q+gJte=6ZwpCNsbd8w@mail.gmail.com> <53FF8722.6080302@redhat.com> <CALCETrVW3ZQ7C6F4tab+UrUy=bX4UepPPrhVNrDtLx=ckz2EpA@mail.gmail.com>
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Il 29/08/2014 02:13, Andy Lutomirski ha scritto:
> Hmm.  Then, assuming that someone manages to allocate a
> cross-hypervisor MSR number for this, what am I supposed to do in the
> KVM code?  Just make it available unconditionally?  I don't see why
> that wouldn't work reliably, but it seems like an odd design.

The odd part of it is what Gleb mentioned.

> Also, the one and only native feature flag I tested (rdtscp) actually
> does work: RDTSCP seems to send #UD if QEMU is passed -cpu
> host,-rdtscp.

True, and I'm not sure why.  There are a couple others.  I was thinking
more of things like SSE, AVX or DE (that affects the availability of a
bit in CR4).

Paolo