Quite frankly it might make more sense to define a cross-VM *cpuid* range. The cpuid leaf can just point to the MSR. The big question is who will be willing to be the registrar. On September 18, 2014 11:35:39 AM PDT, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >On Thu, Sep 18, 2014 at 10:42 AM, Nakajima, Jun ><jun.nakajima@xxxxxxxxx> wrote: >> On Thu, Sep 18, 2014 at 10:20 AM, KY Srinivasan <kys@xxxxxxxxxxxxx> >wrote: >>> >>> >>>> -----Original Message----- >>>> From: Paolo Bonzini [mailto:paolo.bonzini@xxxxxxxxx] 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. >>> >> >> Actually, that MSR address range has been reserved for that purpose, >along with: >> - CPUID.EAX=1 -> ECX bit 31 (always returns 0 on bare metal) >> - CPUID.EAX=4000_00xxH leaves (i.e. HYPERVISOR CPUID) > >I don't know whether this is documented anywhere, but Linux tries to >detect a hypervisor by searching CPUID leaves 0x400xyz00 for >"KVMKVMKVM\0\0\0", so at least Linux can handle the KVM leaves being >in a somewhat variable location. > >Do we consider this mechanism to work across all hypervisors and >guests? That is, could we put something like "CrossHVPara\0" >somewhere in that range, where each hypervisor would be free to decide >exactly where it ends up? > >--Andy -- Sent from my mobile phone. Please pardon brevity and lack of formatting. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
