xen/arm: mpu: Enable MPU

After the regions have been created, now we enable the MPU. For this we disable
the background region so that the new memory map created for the regions take
effect. Also, we treat all RW regions as non executable and the data cache is
enabled.

Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@amd.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Acked-by: Julien Grall <jgrall@amazon.com>

diff --git a/xen/arch/arm/arm64/mpu/head.S b/xen/arch/arm/arm64/mpu/head.S
index a06589566f3989bf1b085703d510d91d07aed444..bacf8315f966e31f2b7fc3bcae73f7b93ff8566f 100644 (file)
--- a/xen/arch/arm/arm64/mpu/head.S
+++ b/xen/arch/arm/arm64/mpu/head.S
@@ -5,6 +5,9 @@
 
 #include <asm/arm64/mpu.h>
 
+/* Backgroud region enable/disable */
+#define SCTLR_ELx_BR    BIT(17, UL)
+
 #define REGION_TEXT_PRBAR       0x38    /* SH=11 AP=10 XN=00 */
 #define REGION_RO_PRBAR         0x3A    /* SH=11 AP=10 XN=10 */
 #define REGION_DATA_PRBAR       0x32    /* SH=11 AP=00 XN=10 */
@@ -75,6 +78,29 @@ FUNC_LOCAL(fail_insufficient_regions)
     b   1b
 END(fail_insufficient_regions)
 
+/*
+ * Enable EL2 MPU and data cache
+ * If the Background region is enabled, then the MPU uses the default memory
+ * map as the Background region for generating the memory
+ * attributes when MPU is disabled.
+ * Since the default memory map of the Armv8-R AArch64 architecture is
+ * IMPLEMENTATION DEFINED, we intend to turn off the Background region here.
+ *
+ * Clobbers x0
+ *
+ */
+FUNC_LOCAL(enable_mpu)
+    mrs   x0, SCTLR_EL2
+    bic   x0, x0, #SCTLR_ELx_BR       /* Disable Background region */
+    orr   x0, x0, #SCTLR_Axx_ELx_M    /* Enable MPU */
+    orr   x0, x0, #SCTLR_Axx_ELx_C    /* Enable D-cache */
+    orr   x0, x0, #SCTLR_Axx_ELx_WXN  /* Enable WXN */
+    msr   SCTLR_EL2, x0
+    isb
+
+    ret
+END(enable_mpu)
+
 /*
  * Maps the various sections of Xen (described in xen.lds.S) as different MPU
  * regions.
@@ -114,6 +140,7 @@ FUNC(enable_boot_cpu_mm)
     ldr   x2, =__bss_end
     prepare_xen_region x0, x1, x2, x3, x4, x5
 
+    b    enable_mpu
     ret
 END(enable_boot_cpu_mm)