x86/sev-es: Handle #AC Events

Implement a handler for #VC exceptions caused by #AC exceptions. The
#AC exception is just forwarded to do_alignment_check() and not pushed
down to the hypervisor, as requested by the SEV-ES GHCB Standardization
Specification.
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-61-joro@8bytes.org

arch/x86/kernel/sev-es.c

@@ -909,6 +909,19 @@ static enum es_result vc_handle_vmmcall(struct ghcb *ghcb,
 	return ES_OK;
 }
 
+static enum es_result vc_handle_trap_ac(struct ghcb *ghcb,
+					struct es_em_ctxt *ctxt)
+{
+	/*
+	 * Calling ecx_alignment_check() directly does not work, because it
+	 * enables IRQs and the GHCB is active. Forward the exception and call
+	 * it later from vc_forward_exception().
+	 */
+	ctxt->fi.vector = X86_TRAP_AC;
+	ctxt->fi.error_code = 0;
+	return ES_EXCEPTION;
+}
+
 static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
 					 struct ghcb *ghcb,
 					 unsigned long exit_code)
@@ -922,6 +935,9 @@ static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
 	case SVM_EXIT_WRITE_DR7:
 		result = vc_handle_dr7_write(ghcb, ctxt);
 		break;
+	case SVM_EXIT_EXCP_BASE + X86_TRAP_AC:
+		result = vc_handle_trap_ac(ghcb, ctxt);
+		break;
 	case SVM_EXIT_RDTSC:
 	case SVM_EXIT_RDTSCP:
 		result = vc_handle_rdtsc(ghcb, ctxt, exit_code);
@@ -981,6 +997,9 @@ static __always_inline void vc_forward_exception(struct es_em_ctxt *ctxt)
 	case X86_TRAP_UD:
 		exc_invalid_op(ctxt->regs);
 		break;
+	case X86_TRAP_AC:
+		exc_alignment_check(ctxt->regs, error_code);
+		break;
 	default:
 		pr_emerg("Unsupported exception in #VC instruction emulation - can't continue\n");
 		BUG();