armv8: Add ARMv8 MPU configuration logic

Armv8r64 is the first Armv8 platform that only has a PMSA at the
current exception level. The architecture supplement for Armv8r64
describes new fields in ID_AA64MMFR0_EL1 which can be used to detect
whether a VMSA or PMSA is present. These fields are RES0 on Armv8a.

Add logic to read these fields and, for the protection of the memory
used by U-Boot, initialize the MPU instead of the MMU during init, then
clear the MPU regions before transition to the next stage.

Provide a default (blank) MPU memory map, which can be overridden by
board configurations.

Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>

arch/arm/cpu/armv8/cache_v8.c

@@ -15,6 +15,7 @@
 #include <asm/global_data.h>
 #include <asm/system.h>
 #include <asm/armv8/mmu.h>
+#include <asm/armv8/mpu.h>
 
 DECLARE_GLOBAL_DATA_PTR;
 
@@ -365,6 +366,86 @@ __weak u64 get_page_table_size(void)
 	return size;
 }
 
+static void mpu_clear_regions(void)
+{
+	int i;
+
+	for (i = 0; mpu_mem_map[i].end || mpu_mem_map[i].attrs; i++) {
+		setup_el2_mpu_region(i, 0, 0);
+	}
+}
+
+static struct mpu_region default_mpu_mem_map[] = {{0,}};
+__weak struct mpu_region *mpu_mem_map = default_mpu_mem_map;
+
+static void mpu_setup(void)
+{
+	int i;
+
+	if (current_el() != 2) {
+		panic("MPU configuration is only supported at EL2");
+	}
+
+	set_sctlr(get_sctlr() & ~(CR_M | CR_WXN));
+
+	asm volatile("msr MAIR_EL2, %0" : : "r" MEMORY_ATTRIBUTES);
+
+	for (i = 0; mpu_mem_map[i].end || mpu_mem_map[i].attrs; i++) {
+		setup_el2_mpu_region(i,
+			PRBAR_ADDRESS(mpu_mem_map[i].start)
+				| PRBAR_OUTER_SH | PRBAR_AP_RW_ANY,
+			PRLAR_ADDRESS(mpu_mem_map[i].end)
+				| mpu_mem_map[i].attrs | PRLAR_EN_BIT
+			);
+	}
+
+	set_sctlr(get_sctlr() | CR_M);
+}
+
+static bool el_has_mmu(void)
+{
+	uint64_t id_aa64mmfr0;
+	asm volatile("mrs %0, id_aa64mmfr0_el1"
+			: "=r" (id_aa64mmfr0) : : "cc");
+	uint64_t msa = id_aa64mmfr0 & ID_AA64MMFR0_EL1_MSA_MASK;
+	uint64_t msa_frac = id_aa64mmfr0 & ID_AA64MMFR0_EL1_MSA_FRAC_MASK;
+
+	switch (msa) {
+		case ID_AA64MMFR0_EL1_MSA_VMSA:
+			/*
+			 * VMSA supported in all translation regimes.
+			 * No support for PMSA.
+			 */
+			return true;
+		case ID_AA64MMFR0_EL1_MSA_USE_FRAC:
+			/* See MSA_frac for the supported MSAs. */
+			switch (msa_frac) {
+				case ID_AA64MMFR0_EL1_MSA_FRAC_NO_PMSA:
+					/*
+					 * PMSA not supported in any translation
+					 * regime.
+					 */
+					return true;
+				case ID_AA64MMFR0_EL1_MSA_FRAC_VMSA:
+					/*
+					* PMSA supported in all translation
+					* regimes. No support for VMSA.
+					*/
+				case ID_AA64MMFR0_EL1_MSA_FRAC_PMSA:
+					/*
+					 * PMSA supported in all translation
+					 * regimes.
+					 */
+					return false;
+				default:
+					panic("Unsupported id_aa64mmfr0_el1 " \
+						"MSA_frac value");
+			}
+		default:
+			panic("Unsupported id_aa64mmfr0_el1 MSA value");
+	}
+}
+
 void setup_pgtables(void)
 {
 	int i;
@@ -479,8 +560,13 @@ void dcache_enable(void)
 	/* The data cache is not active unless the mmu is enabled */
 	if (!(get_sctlr() & CR_M)) {
 		invalidate_dcache_all();
-		__asm_invalidate_tlb_all();
+
-		mmu_setup();
+		if (el_has_mmu()) {
+			__asm_invalidate_tlb_all();
+			mmu_setup();
+		} else {
+			mpu_setup();
+		}
 	}
 
 	set_sctlr(get_sctlr() | CR_C);
@@ -499,7 +585,11 @@ void dcache_disable(void)
 	set_sctlr(sctlr & ~(CR_C|CR_M));
 
 	flush_dcache_all();
-	__asm_invalidate_tlb_all();
+
+	if (el_has_mmu())
+		__asm_invalidate_tlb_all();
+	else
+		mpu_clear_regions();
 }
 
 int dcache_status(void)

arch/arm/include/asm/armv8/mpu.h

@@ -0,0 +1,61 @@
+/*
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ * (C) Copyright 2021 Arm Limited
+ */
+
+#ifndef _ASM_ARMV8_MPU_H_
+#define _ASM_ARMV8_MPU_H_
+
+#include <asm/armv8/mmu.h>
+#include <asm/barriers.h>
+#include <linux/stringify.h>
+
+#define PRSELR_EL2		S3_4_c6_c2_1
+#define PRBAR_EL2		S3_4_c6_c8_0
+#define PRLAR_EL2		S3_4_c6_c8_1
+#define MPUIR_EL2		S3_4_c0_c0_4
+
+#define PRBAR_ADDRESS(addr)	((addr) & ~(0x3fULL))
+
+/* Access permissions */
+#define PRBAR_AP(val)		(((val) & 0x3) << 2)
+#define PRBAR_AP_RW_HYP		PRBAR_AP(0x0)
+#define PRBAR_AP_RW_ANY		PRBAR_AP(0x1)
+#define PRBAR_AP_RO_HYP		PRBAR_AP(0x2)
+#define PRBAR_AP_RO_ANY		PRBAR_AP(0x3)
+
+/* Shareability */
+#define PRBAR_SH(val)		(((val) & 0x3) << 4)
+#define PRBAR_NON_SH		PRBAR_SH(0x0)
+#define PRBAR_OUTER_SH		PRBAR_SH(0x2)
+#define PRBAR_INNER_SH		PRBAR_SH(0x3)
+
+/* Memory attribute (MAIR idx) */
+#define PRLAR_ATTRIDX(val)	(((val) & 0x7) << 1)
+#define PRLAR_EN_BIT		(0x1)
+#define PRLAR_ADDRESS(addr)	((addr) & ~(0x3fULL))
+
+#ifndef __ASSEMBLY__
+
+static inline void setup_el2_mpu_region(uint8_t region, uint64_t base, uint64_t limit)
+{
+	asm volatile("msr " __stringify(PRSELR_EL2) ", %0" : : "r" (region));
+	isb();
+	asm volatile("msr " __stringify(PRBAR_EL2) ", %0" : : "r" (base));
+	asm volatile("msr " __stringify(PRLAR_EL2) ", %0" : : "r" (limit));
+	dsb();
+	isb();
+}
+
+#endif
+
+struct mpu_region {
+	u64 start;
+	u64 end;
+	u64 attrs;
+};
+
+extern struct mpu_region *mpu_mem_map;
+
+#endif /* _ASM_ARMV8_MPU_H_ */