Re: [PATCH v5 3/6] x86/sev-es: Split up runtime #VC handler for correct state tracking

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S

@@ -506,7 +506,7 @@ SYM_CODE_START(\asmsym)
 
 	movq	%rsp, %rdi		/* pt_regs pointer */
 
-	call	\cfunc
+	call	kernel_\cfunc
 
 	/*
 	 * No need to switch back to the IST stack. The current stack is either

@@ -517,7 +517,7 @@ SYM_CODE_START(\asmsym)
 
 	/* Switch to the regular task stack */
 .Lfrom_usermode_switch_stack_\@:
-	idtentry_body safe_stack_\cfunc, has_error_code=1
+	idtentry_body user_\cfunc, has_error_code=1
 
 _ASM_NOKPROBE(\asmsym)
 SYM_CODE_END(\asmsym)

+static bool noinstr vc_check_and_handle_db(struct pt_regs *regs, unsigned long error_code)
+{
+	if (likely(error_code != SVM_EXIT_EXCP_BASE + X86_TRAP_DB))
+		return false;
 
+	vc_handle_trap_db(regs);

+
+	return true;
+}

+
+/*
+ * Runtime #VC exception handler when raised from kernel mode. Runs in NMI mode
+ * and will panic when an error happens.
+ */
+DEFINE_IDTENTRY_VC_KERNEL(exc_vmm_communication)
+{
+	irqentry_state_t irq_state;
 
+	/*
+	 * With the current implementation it is always possible to switch to a
+	 * safe stack because #VC exceptions only happen at known places, like
+	 * intercepted instructions or accesses to MMIO areas/IO ports. They can
+	 * also happen with code instrumentation when the hypervisor intercepts
+	 * #DB, but the critical paths are forbidden to be instrumented, so #DB
+	 * exceptions currently also only happen in safe places.
+	 *
+	 * But keep this here in case the noinstr annotations are violated due
+	 * to bug elsewhere.
+	 */
+	if (unlikely(on_vc_fallback_stack(regs))) {
+		instrumentation_begin();
+		panic("Can't handle #VC exception from unsupported context\n");
+		instrumentation_end();
+	}
+
+	/*
+	 * Handle #DB before calling into !noinstr code to avoid recursive #DB.
+	 */
+	if (vc_check_and_handle_db(regs, error_code))
+		return;

+
+	irq_state = irqentry_nmi_enter(regs);
+
+	instrumentation_begin();
+
+	if (!vc_raw_handle_exception(regs, error_code)) {
 		/* Show some debug info */
 		show_regs(regs);
 

@@ -1443,23 +1448,38 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
 		panic("Returned from Terminate-Request to Hypervisor\n");
 	}
 
+	instrumentation_end();
+	irqentry_nmi_exit(regs, irq_state);
 }
 
+/*
+ * Runtime #VC exception handler when raised from user mode. Runs in IRQ mode
+ * and will kill the current task with SIGBUS when an error happens.
+ */
+DEFINE_IDTENTRY_VC_USER(exc_vmm_communication)
 {
+	irqentry_state_t irq_state;
+
+	/*
+	 * Handle #DB before calling into !noinstr code to avoid recursive #DB.
+	 */
+	if (vc_check_and_handle_db(regs, error_code))
+		return;

+
+	irq_state = irqentry_enter(regs);
 	instrumentation_begin();
 
+	if (!vc_raw_handle_exception(regs, error_code)) {
+		/*
+		 * Do not kill the machine if user-space triggered the
+		 * exception. Send SIGBUS instead and let user-space deal with
+		 * it.
+		 */
+		force_sig_fault(SIGBUS, BUS_OBJERR, (void __user *)0);
+	}
+
+	instrumentation_end();
+	irqentry_exit(regs, irq_state);
 }