linux-kernel - Re: [PATCH RFC 01/39] KVM: x86: fix Xen hypercall page msr handling

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Date:   Fri, 22 Feb 2019 13:51:23 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Joao Martins <joao.m.martins@...cle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ankur Arora <ankur.a.arora@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH RFC 01/39] KVM: x86: fix Xen hypercall page msr handling

On 22/02/19 02:30, Sean Christopherson wrote:
> 	if (kvm_advertise_kvm()) {
> 		if (<handle kvm msr>)
> 			return ...;
> 	} else if (kvm_advertise_hyperv()) {
> 		if (<handle hyperv msr>)
> 			return ...;
> 	} else if (kvm_advertise_xen()) {
> 		if (<handle xen msrs>)
> 			return ...;
> 	}
> 
> 	<fall through to main switch statement>
> 
> Obviously assumes KVM only advertises itself as one hypervisor, and so
> the ordering is arbitrary.

No, KVM can advertise as both KVM and Hyper-V.  CPUID 0x40000000 is used
for Hyper-V, while 0x40000100 is used for KVM.  The MSRs do not conflict.

Paolo