Re: [PATCH RFC v8 34/56] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_START command

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On 4/26/23 12:06, Sabin Rapan wrote:
On 20.02.2023 20:38, Michael Roth wrote:
From: Brijesh Singh <brijesh.singh@xxxxxxx>

+static int snp_decommission_context(struct kvm *kvm)
+{
+	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+	struct sev_data_snp_addr data = {};
+	int ret;
+
+	/* If context is not created then do nothing */
+	if (!sev->snp_context)
+		return 0;
+
+	data.gctx_paddr = __sme_pa(sev->snp_context);
+	ret = sev_do_cmd(SEV_CMD_SNP_DECOMMISSION, &data, NULL);
+	if (WARN_ONCE(ret, "failed to release guest context"))
+		return ret;
+
+	/* free the context page now */
+	snp_free_firmware_page(sev->snp_context);
+	sev->snp_context = NULL;
+
+	return 0;
+}
+

Even though it's not documented, SNP_DECOMMISSION seems to clear the
WBINVD indicator just like DEACTIVATE does for SEV.
Won't ASID recycling race with SNP_DECOMMISSION if the latter isn't
guarded with sev_deactivate_lock?

Good catch, yes, this needs to use the sev_deactivate_lock around the DECOMMISSION command.

Thanks,
Tom



  void sev_vm_destroy(struct kvm *kvm)
  {
  	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
@@ -2333,7 +2440,15 @@ void sev_vm_destroy(struct kvm *kvm)
  		}
  	}
- sev_unbind_asid(kvm, sev->handle);
+	if (sev_snp_guest(kvm)) {
+		if (snp_decommission_context(kvm)) {
+			WARN_ONCE(1, "Failed to free SNP guest context, leaking asid!\n");
+			return;
+		}
+	} else {
+		sev_unbind_asid(kvm, sev->handle);
+	}
+
  	sev_asid_free(sev);
  }



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