stm32h7: Keep protected user SRAM non-shareable.

The generic ARMv7-M user SRAM helper marks memory shareable.  STM32H7
Protected user data and heaps can reside in cacheable AXI or D2 SRAM, where
userspace synchronization needs LDREX/STREX to use the CPU-local exclusive
monitor.

Map protected user SRAM as Normal, cacheable, and non-shareable.  Dual-core
RPTUN SRAM remains unaffected because it is mapped separately with explicit
shareable attributes.

Tested by booting a Protected image and running user and kernel work-queue
stress tests on an STM32H7 PX4 FMUv6C.

Assisted-by: Codex:GPT-5
Signed-off-by: DuoYuWang <thirteenking.wang@gmail.com>

Author: 13022591351

arch/arm/src/stm32h7/stm32_mpuinit.c

@@ -52,6 +52,26 @@
 #  endif
 #endif
 
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+#ifdef CONFIG_BUILD_PROTECTED
+static void stm32_mpu_user_intsram(uintptr_t start, size_t size)
+{
+  /* STM32H7 protected user memory can span AXI and D2 SRAM.  Keep it
+   * Normal and non-shareable so that LDREX/STREX use the CPU-local
+   * exclusive monitor.  Dual-core RPTUN shared memory is mapped separately
+   * below with shareable attributes.
+   */
+
+  mpu_configure_region(start, size,
+                       MPU_RASR_TEX_SO |
+                       MPU_RASR_C |
+                       MPU_RASR_AP_RWRW);
+}
+#endif
+
 /****************************************************************************
  * Public Functions
  ****************************************************************************/
@@ -94,7 +114,7 @@ void stm32_mpuinitialize(void)
   mpu_user_flash(USERSPACE->us_textstart,
                  USERSPACE->us_textend - USERSPACE->us_textstart);
 
-  mpu_user_intsram(datastart, dataend - datastart);
+  stm32_mpu_user_intsram(datastart, dataend - datastart);
 #endif
 
 #ifdef CONFIG_RPTUN
@@ -121,7 +141,7 @@ void stm32_mpuinitialize(void)
 
 void stm32_mpu_uheap(uintptr_t start, size_t size)
 {
-  mpu_user_intsram(start, size);
+  stm32_mpu_user_intsram(start, size);
 }
 #endif