linux-kernel - Re: GET_RNG_SEED hypercall ABI? (Re: [PATCH v5 0/5] random,x86,kvm: Rework arch RNG seeds and get some from kvm)

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Date:	Fri, 29 Aug 2014 08:36:47 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Gleb Natapov <gleb@...nel.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	"Theodore Ts'o" <tytso@....edu>, Kees Cook <keescook@...omium.org>,
	kvm list <kvm@...r.kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Bandan Das <bsd@...hat.com>, Andrew Honig <ahonig@...gle.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Alok Kataria <akataria@...are.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)

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
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