[PATCH 2/2] KVM: SEV: Allow launch vmsa from mirror VM

[Peter Gonda]

A mirrored SEV-ES VM will need to call KVM_SEV_LAUNCH_UPDATE_VMSA to
setup its vCPUs and add them to the SEV-ES VM. Since they need to be
measured and their VMSAs encrypted. Also allow the guest status check
and debugging commands since they do not change any guest state.

Signed-off-by: Peter Gonda <pgonda@xxxxxxxxxx>
Cc: Marc Orr <marcorr@xxxxxxxxxx>
Cc: Nathan Tempelman <natet@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Cc: Steve Rutherford <srutherford@xxxxxxxxxx>
Cc: Brijesh Singh <brijesh.singh@xxxxxxx>
Cc: kvm@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx

---
 arch/x86/kvm/svm/sev.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 08c53a4e060e..9cb6e30d6ae4 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1501,6 +1501,20 @@ static int sev_receive_finish(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	return sev_issue_cmd(kvm, SEV_CMD_RECEIVE_FINISH, &data, &argp->error);
 }
 
+static bool cmd_allowed_from_miror(u32 cmd_id)
+{
+	/*
+	 * Allow mirrors VM to call KVM_SEV_LAUNCH_UPDATE_VMSA to enable SEV-ES
+	 * active mirror VMs. Also allow the debugging and status commands.
+	 */
+	if (cmd_id == KVM_SEV_LAUNCH_UPDATE_VMSA ||
+	    cmd_id == KVM_SEV_GUEST_STATUS || cmd_id == KVM_SEV_DBG_DECRYPT ||
+	    cmd_id == KVM_SEV_DBG_ENCRYPT)
+		return true;
+
+	return false;
+}
+
 int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
 {
 	struct kvm_sev_cmd sev_cmd;
@@ -1517,8 +1531,9 @@ int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
 
 	mutex_lock(&kvm->lock);
 
-	/* enc_context_owner handles all memory enc operations */
-	if (is_mirroring_enc_context(kvm)) {
+	/* Only the enc_context_owner handles some memory enc operations. */
+	if (is_mirroring_enc_context(kvm) &&
+	    !cmd_allowed_from_miror(sev_cmd.id)) {
 		r = -EINVAL;
 		goto out;
 	}
-- 
2.33.0.464.g1972c5931b-goog