cpu/x86/smm: Add support for exception handling

Add an exception handler to SMM to debug crashes when a serial
console is enabled and DEBUG_SMI is set. This allows for narrowing
down issues faster than letting the machine triple fault.

Change-Id: I2ccaf8d23d508d773ce56912983884ad6832ede6
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/87208
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Shuo Liu <shuo.liu@intel.com>
Reviewed-by: Maximilian Brune <maximilian.brune@9elements.com>

src/arch/x86/exception.c

@@ -665,6 +665,8 @@ asmlinkage void exception_init(void)
 
 	load_idt(idt, sizeof(idt));
 
+#if !ENV_SMM
 	null_breakpoint_init();
 	stack_canary_breakpoint_init();
+#endif
 }

src/cpu/x86/smm/smm_module_handler.c

@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
 #include <arch/io.h>
+#include <arch/exception.h>
 #include <commonlib/region.h>
 #include <console/cbmem_console.h>
 #include <console/console.h>
@@ -169,6 +170,9 @@ asmlinkage void smm_handler_start(void *arg)
 
 	printk(BIOS_SPEW, "\nSMI# #%d\n", cpu);
 
+	if (CONFIG(DEBUG_SMI) && CONFIG(CONSOLE_SERIAL))
+		exception_init();
+
 	/* Allow drivers to initialize variables in SMM context. */
 	if (do_driver_init) {
 #if CONFIG(SPI_FLASH_SMM)