From mboxrd@z Thu Jan  1 00:00:00 1970
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: Standardizing an MSR or other hypercall to get an RNG seed?
Date: Fri, 19 Sep 2014 10:18:37 -0700
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Cc: Mathew John <mathewj@microsoft.com>, Theodore Ts'o <tytso@mit.edu>,
	David Hepkin <davidhep@microsoft.com>, kvm list <kvm@vger.kernel.org>,
	Niels Ferguson <niels@microsoft.com>,
	Andy Lutomirski <luto@amacapital.net>, Jake Oshins <jakeo@microsoft.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Linux Virtualization <virtualization@lists.linux-foundation.org>,
	John Starks <John.Starks@microsoft.com>
To: Gleb Natapov <gleb@kernel.org>
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On 09/19/2014 10:15 AM, Gleb Natapov wrote:
> On Fri, Sep 19, 2014 at 10:08:20AM -0700, H. Peter Anvin wrote:
>> On 09/19/2014 09:53 AM, Gleb Natapov wrote:
>>> On Fri, Sep 19, 2014 at 09:40:07AM -0700, H. Peter Anvin wrote:
>>>> On 09/19/2014 09:37 AM, Gleb Natapov wrote:
>>>>>
>>>>> Linux detects what hypervior it runs on very early
>>>>
>>>> Not anywhere close to early enough.  We're talking for uses like kASLR.
>>>>
>>> Still to early to do:
>>>
>>>    h = cpuid(HYPERVIOR_SIGNATURE)
>>>    if (h == KVMKVMKVM) {
>>>       if (cpuid(kvm_features) & kvm_rnd)
>>>          rdmsr(kvm_rnd)
>>>    else (h == HyperV) {
>>>       if (cpuid(hv_features) & hv_rnd)
>>>         rdmsr(hv_rnd) 
>>>    else (h == XenXenXen) {
>>>       if (cpuid(xen_features) & xen_rnd)
>>>         rdmsr(xen_rnd)
>>>   }
>>>
>>
>> If we need to do chase loops, especially not so...
>>
> What loops exactly? As a non native English speaker I fail to understand
> if your answer is "yes" or "no" ;)
> 

The above isn't actually the full algorithm used.

	-hpa