From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: Standardizing an MSR or other hypercall to get an RNG seed?
Date: Fri, 19 Sep 2014 18:22:24 +0200
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To: "Nakajima, Jun" <jun.nakajima@intel.com>, Andy Lutomirski <luto@amacapital.net>
Cc: Mathew John <mathewj@microsoft.com>, Theodore Ts'o <tytso@mit.edu>, John Starks <John.Starks@microsoft.com>, kvm list <kvm@vger.kernel.org>, Gleb Natapov <gleb@kernel.org>, Niels Ferguson <niels@microsoft.com>, Linux Virtualization <virtualization@lists.linux-foundation.org>, David Hepkin <davidhep@microsoft.com>, "H. Peter Anvin" <hpa@zytor.com>, Jake Oshins <jakeo@microsoft.com>
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Il 19/09/2014 18:14, Nakajima, Jun ha scritto:
> For example,
> - CPUID 0x48000001.EAX would return the feature presence (e.g. in
> EBX), and the result in EDX:EAX (if present) at the same time, or
> - CPUID 0x48000001.EAX would return the feature presence only, and
> CPUID 0x48000002.EAX (acts like a hypercall) returns up to 4 32-bit
> values.

The latter is much better, because an "unknown" CPUID will return the
value of the highest leaf below 0x80000000, and conflicts can happen easily.

Paolo