From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.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)
Date: Fri, 29 Aug 2014 08:36:47 +0200
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Cc: X86 ML <x86@kernel.org>, Theodore Ts'o <tytso@mit.edu>,
	Kees Cook <keescook@chromium.org>, kvm list <kvm@vger.kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Gleb Natapov <gleb@kernel.org>, Andrew Honig <ahonig@google.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Linux Virtualization <virtualization@lists.linux-foundation.org>,
	Daniel Borkmann <dborkman@redhat.com>, Bandan Das <bsd@redhat.com>,
	Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
	Alok Kataria <akataria@vmware.com>, "H. Peter Anvin" <hpa@zytor.com>
To: Andy Lutomirski <luto@amacapital.net>
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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