linux-kernel - Re: [PATCH v14 03/22] KVM: SEV: Add GHCB handling for Hypervisor Feature Support requests

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Message-ID: <Zilp3Sp5S-sljoQE@google.com>
Date: Wed, 24 Apr 2024 13:21:49 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Michael Roth <michael.roth@....com>
Cc: kvm@...r.kernel.org, linux-coco@...ts.linux.dev, linux-mm@...ck.org, 
	linux-crypto@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org, 
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	thomas.lendacky@....com, hpa@...or.com, ardb@...nel.org, pbonzini@...hat.com, 
	vkuznets@...hat.com, jmattson@...gle.com, luto@...nel.org, 
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	peterz@...radead.org, srinivas.pandruvada@...ux.intel.com, 
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	sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com, 
	jarkko@...nel.org, ashish.kalra@....com, nikunj.dadhania@....com, 
	pankaj.gupta@....com, liam.merwick@...cle.com, 
	Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v14 03/22] KVM: SEV: Add GHCB handling for Hypervisor
 Feature Support requests

On Sun, Apr 21, 2024, Michael Roth wrote:
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 6e31cb408dd8..1d2264e93afe 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -33,9 +33,11 @@
>  #include "cpuid.h"
>  #include "trace.h"
>  
> -#define GHCB_VERSION_MAX	1ULL
> +#define GHCB_VERSION_MAX	2ULL
>  #define GHCB_VERSION_MIN	1ULL

This needs a userspace control.  Being unable to limit the GHCB version advertised
to the guest is going to break live migration of SEV-ES VMs, e.g. if a pool of
hosts has some kernels running this flavor of KVM, and some hosts running an
older KVM that doesn't support v2.