KVM: SEV: Drop GHCB_VERSION_DEFAULT and open code it

Remove the GHCB_VERSION_DEFAULT macro and open code it with '2'. The macro
is used conditionally and is not a true default. KVM ABI does not
advertise/emumerates the default GHCB version. Any future change to this
macro would silently alter the ABI and potentially break existing
deployments that rely on the current behavior.

Additionally, move the GHCB version assignment earlier in the code flow and
update the comment to clarify that KVM_SEV_INIT2 defaults to version 2,
while KVM_SEV_INIT forces version 1.

No functional change intended.

Cc: Thomas Lendacky <thomas.lendacky@amd.com>
Cc: Michael Roth <michael.roth@amd.com>
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
Link: https://lore.kernel.org/r/20250819234833.3080255-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: nikunjad

arch/x86/kvm/svm/sev.c

@@ -37,7 +37,6 @@
 #include "trace.h"
 
 #define GHCB_VERSION_MAX	2ULL
-#define GHCB_VERSION_DEFAULT	2ULL
 #define GHCB_VERSION_MIN	1ULL
 
 #define GHCB_HV_FT_SUPPORTED	(GHCB_HV_FT_SNP | GHCB_HV_FT_SNP_AP_CREATION)
@@ -421,6 +420,14 @@ static int __sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp,
 	if (data->ghcb_version > GHCB_VERSION_MAX || (!es_active && data->ghcb_version))
 		return -EINVAL;
 
+	/*
+	 * KVM supports the full range of mandatory features defined by version
+	 * 2 of the GHCB protocol, so default to that for SEV-ES guests created
+	 * via KVM_SEV_INIT2 (KVM_SEV_INIT forces version 1).
+	 */
+	if (es_active && !data->ghcb_version)
+		data->ghcb_version = 2;
+
 	if (unlikely(sev->active))
 		return -EINVAL;
 
@@ -429,14 +436,6 @@ static int __sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp,
 	sev->vmsa_features = data->vmsa_features;
 	sev->ghcb_version = data->ghcb_version;
 
-	/*
-	 * Currently KVM supports the full range of mandatory features defined
-	 * by version 2 of the GHCB protocol, so default to that for SEV-ES
-	 * guests created via KVM_SEV_INIT2.
-	 */
-	if (sev->es_active && !sev->ghcb_version)
-		sev->ghcb_version = GHCB_VERSION_DEFAULT;
-
 	if (vm_type == KVM_X86_SNP_VM)
 		sev->vmsa_features |= SVM_SEV_FEAT_SNP_ACTIVE;