xtensa: userspace: handle DTLB multihit exception

This adds a function to handle DTLB multihit exception when
userspace is enabled, as this exception may be raised due to
the same page being able to accessed by both kernel and user
threads. The auto-refill DTLBs may contain entries for same
page, one for kernel and one for user under some situations.
We need to invalidate those existing DTLB entries so that
hardware can reload from the page table.

This is an alternative to the kconfig invalidating DTLBs on
every swap: CONFIG_XTENSA_MMU_FLUSH_AUTOREFILL_DTLBS_ON_SWAP.
Although this does not have extra processing per context
switching, exception handling itself has a high cost. So
care needs to be taken on whether to enable that kconfig.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>

Author: dcpleung

arch/xtensa/core/ptables.c

@@ -1173,6 +1173,16 @@ int arch_buffer_validate(const void *addr, size_t size, int write)
 	return mem_buffer_validate(addr, size, write, XTENSA_MMU_USER_RING);
 }
 
+void xtensa_exc_dtlb_multihit_handle(void)
+{
+	/* For some unknown reasons, using xtensa_dtlb_probe() would result in
+	 * QEMU raising privileged instruction exception. So for now, just
+	 * invalidate all auto-refilled DTLBs.
+	 */
+
+	xtensa_dtlb_autorefill_invalidate();
+}
+
 bool xtensa_exc_load_store_ring_error_check(void *bsa_p)
 {
 	uintptr_t ring, vaddr;

arch/xtensa/core/vector_handlers.c

@@ -3,6 +3,7 @@
  *
  * SPDX-License-Identifier: Apache-2.0
  */
+#include "xtensa/corebits.h"
 #include <string.h>
 #include <xtensa_asm2_context.h>
 #include <zephyr/kernel.h>
@@ -631,6 +632,9 @@ void *xtensa_excint1_c(void *esf)
 		break;
 #endif /* CONFIG_XTENSA_LAZY_HIFI_SHARING */
 #if defined(CONFIG_XTENSA_MMU) && defined(CONFIG_USERSPACE)
+	case EXCCAUSE_DTLB_MULTIHIT:
+		xtensa_exc_dtlb_multihit_handle();
+		break;
 	case EXCCAUSE_LOAD_STORE_RING:
 		if (!xtensa_exc_load_store_ring_error_check(bsa)) {
 			break;

arch/xtensa/include/xtensa_internal.h

@@ -74,6 +74,14 @@ void xtensa_userspace_enter(k_thread_entry_t user_entry,
  */
 bool xtensa_mem_kernel_has_access(const void *addr, size_t size, int write);
 
+/**
+ * @brief Handle DTLB multihit exception.
+ *
+ * Handle DTLB multihit exception by invalidating all auto-refilled DTLBs of
+ * a particular memory page.
+ */
+void xtensa_exc_dtlb_multihit_handle(void);
+
 /**
  * @brief Check if it is a true load/store ring exception.
  *