x86/sev-es: Handle VMMCALL Events

Implement a handler for #VC exceptions caused by VMMCALL instructions.
This is only a starting point, VMMCALL emulation under SEV-ES needs
further hypervisor-specific changes to provide additional state.

 [ bp: Drop "this patch". ]

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
[ jroedel@suse.de: Adapt to #VC handling infrastructure ]
Co-developed-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-60-joro@8bytes.org

Author: tlendacky

arch/x86/kernel/sev-es.c

@@ -889,6 +889,26 @@ static enum es_result vc_handle_mwait(struct ghcb *ghcb,
 	return ES_OK;
 }
 
+static enum es_result vc_handle_vmmcall(struct ghcb *ghcb,
+					struct es_em_ctxt *ctxt)
+{
+	enum es_result ret;
+
+	ghcb_set_rax(ghcb, ctxt->regs->ax);
+	ghcb_set_cpl(ghcb, user_mode(ctxt->regs) ? 3 : 0);
+
+	ret = sev_es_ghcb_hv_call(ghcb, ctxt, SVM_EXIT_VMMCALL, 0, 0);
+	if (ret != ES_OK)
+		return ret;
+
+	if (!ghcb_rax_is_valid(ghcb))
+		return ES_VMM_ERROR;
+
+	ctxt->regs->ax = ghcb->save.rax;
+
+	return ES_OK;
+}
+
 static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
 					 struct ghcb *ghcb,
 					 unsigned long exit_code)
@@ -922,6 +942,9 @@ static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
 	case SVM_EXIT_MSR:
 		result = vc_handle_msr(ghcb, ctxt);
 		break;
+	case SVM_EXIT_VMMCALL:
+		result = vc_handle_vmmcall(ghcb, ctxt);
+		break;
 	case SVM_EXIT_WBINVD:
 		result = vc_handle_wbinvd(ghcb, ctxt);
 		break;