Linux Virtualization - Sep 2014 - Standardizing an MSR or other hypercall to get an RNG seed?

On Thu, Sep 18, 2014 at 9:36 AM, KY Srinivasan <kys at microsoft.com>
wrote:
>
> I am copying other Hyper-V engineers to this discussion.
>
Thanks, K.Y.

In terms of the address for the MSR, I suggest that you choose one
from the range between 40000000H - 400000FFH. The SDM (35.1
ARCHITECTURAL MSRS) says "All existing and
future processors will not implement any features using any MSR in
this range." Hyper-V already defines many synthetic MSRs in this
range, and I think it would be reasonable for you to pick one for this
to avoid a conflict?

-- 
Jun
Intel Open Source Technology Center

Il 18/09/2014 19:13, Nakajima, Jun ha scritto:
> In terms of the address for the MSR, I suggest that you choose one
> from the range between 40000000H - 400000FFH. The SDM (35.1
> ARCHITECTURAL MSRS) says "All existing and
> future processors will not implement any features using any MSR in
> this range." Hyper-V already defines many synthetic MSRs in this
> range, and I think it would be reasonable for you to pick one for this
> to avoid a conflict?
KVM is not using any MSR in that range.

However, I think it would be better to have the MSR (and perhaps CPUID)
outside the hypervisor-reserved ranges, so that it becomes
architecturally defined.  In some sense it is similar to the HYPERVISOR
CPUID feature.

Paolo

That certainly sound reasonable to me.  How do you see discovery of that
working?

Thanks,
Jake Oshins


-----Original Message-----
From: Paolo Bonzini [mailto:paolo.bonzini at gmail.com] On Behalf Of Paolo
Bonzini
Sent: Thursday, September 18, 2014 10:18 AM
To: Nakajima, Jun; KY Srinivasan
Cc: Mathew John; Theodore Ts'o; John Starks; kvm list; Gleb Natapov; Niels
Ferguson; Andy Lutomirski; David Hepkin; H. Peter Anvin; Jake Oshins; Linux
Virtualization
Subject: Re: Standardizing an MSR or other hypercall to get an RNG seed?

Il 18/09/2014 19:13, Nakajima, Jun ha scritto:
> In terms of the address for the MSR, I suggest that you choose one
> from the range between 40000000H - 400000FFH. The SDM (35.1
> ARCHITECTURAL MSRS) says "All existing and
> future processors will not implement any features using any MSR in
> this range." Hyper-V already defines many synthetic MSRs in this
> range, and I think it would be reasonable for you to pick one for this
> to avoid a conflict?
KVM is not using any MSR in that range.

However, I think it would be better to have the MSR (and perhaps CPUID)
outside the hypervisor-reserved ranges, so that it becomes
architecturally defined.  In some sense it is similar to the HYPERVISOR
CPUID feature.

Paolo

> -----Original Message-----
> From: Paolo Bonzini [mailto:paolo.bonzini at gmail.com] On Behalf Of Paolo
> Bonzini
> Sent: Thursday, September 18, 2014 10:18 AM
> To: Nakajima, Jun; KY Srinivasan
> Cc: Mathew John; Theodore Ts'o; John Starks; kvm list; Gleb Natapov;
Niels
> Ferguson; Andy Lutomirski; David Hepkin; H. Peter Anvin; Jake Oshins; Linux
> Virtualization
> Subject: Re: Standardizing an MSR or other hypercall to get an RNG seed?
> 
> Il 18/09/2014 19:13, Nakajima, Jun ha scritto:
> > In terms of the address for the MSR, I suggest that you choose one
> > from the range between 40000000H - 400000FFH. The SDM (35.1
> > ARCHITECTURAL MSRS) says "All existing and future processors will
not
> > implement any features using any MSR in this range." Hyper-V
already
> > defines many synthetic MSRs in this range, and I think it would be
> > reasonable for you to pick one for this to avoid a conflict?
> 
> KVM is not using any MSR in that range.
> 
> However, I think it would be better to have the MSR (and perhaps CPUID)
> outside the hypervisor-reserved ranges, so that it becomes architecturally
> defined.  In some sense it is similar to the HYPERVISOR CPUID feature.
Yes, given that we want this to be hypervisor agnostic.

K. Y