arm64: Detect if in a realm and set RIPAS RAM

Detect that the VM is a realm guest by the presence of the RSI
interface. This is done after PSCI has been initialised so that we can
check the SMCCC conduit before making any RSI calls.

If in a realm then iterate over all memory ensuring that it is marked as
RIPAS RAM. The loader is required to do this for us, however if some
memory is missed this will cause the guest to receive a hard to debug
external abort at some random point in the future. So for a
belt-and-braces approach set all memory to RIPAS RAM. Any failure here
implies that the RAM regions passed to Linux are incorrect so panic()
promptly to make the situation clear.

Reviewed-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Co-developed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://lore.kernel.org/r/20241017131434.40935-3-steven.price@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/rsi.h

@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2024 ARM Ltd.
+ */
+
+#ifndef __ASM_RSI_H_
+#define __ASM_RSI_H_
+
+#include <linux/errno.h>
+#include <linux/jump_label.h>
+#include <asm/rsi_cmds.h>
+
+DECLARE_STATIC_KEY_FALSE(rsi_present);
+
+void __init arm64_rsi_init(void);
+
+static inline bool is_realm_world(void)
+{
+	return static_branch_unlikely(&rsi_present);
+}
+
+static inline int rsi_set_memory_range(phys_addr_t start, phys_addr_t end,
+				       enum ripas state, unsigned long flags)
+{
+	unsigned long ret;
+	phys_addr_t top;
+
+	while (start != end) {
+		ret = rsi_set_addr_range_state(start, end, state, flags, &top);
+		if (ret || top < start || top > end)
+			return -EINVAL;
+		start = top;
+	}
+
+	return 0;
+}
+
+/*
+ * Convert the specified range to RAM. Do not use this if you rely on the
+ * contents of a page that may already be in RAM state.
+ */
+static inline int rsi_set_memory_range_protected(phys_addr_t start,
+						 phys_addr_t end)
+{
+	return rsi_set_memory_range(start, end, RSI_RIPAS_RAM,
+				    RSI_CHANGE_DESTROYED);
+}
+
+/*
+ * Convert the specified range to RAM. Do not convert any pages that may have
+ * been DESTROYED, without our permission.
+ */
+static inline int rsi_set_memory_range_protected_safe(phys_addr_t start,
+						      phys_addr_t end)
+{
+	return rsi_set_memory_range(start, end, RSI_RIPAS_RAM,
+				    RSI_NO_CHANGE_DESTROYED);
+}
+
+static inline int rsi_set_memory_range_shared(phys_addr_t start,
+					      phys_addr_t end)
+{
+	return rsi_set_memory_range(start, end, RSI_RIPAS_EMPTY,
+				    RSI_CHANGE_DESTROYED);
+}
+#endif /* __ASM_RSI_H_ */

arch/arm64/kernel/Makefile

@@ -33,7 +33,8 @@ obj-y			:= debug-monitors.o entry.o irq.o fpsimd.o		\
 			   return_address.o cpuinfo.o cpu_errata.o		\
 			   cpufeature.o alternative.o cacheinfo.o		\
 			   smp.o smp_spin_table.o topology.o smccc-call.o	\
-			   syscall.o proton-pack.o idle.o patching.o pi/
+			   syscall.o proton-pack.o idle.o patching.o pi/	\
+			   rsi.o
 
 obj-$(CONFIG_COMPAT)			+= sys32.o signal32.o			\
 					   sys_compat.o

arch/arm64/kernel/rsi.c

@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023 ARM Ltd.
+ */
+
+#include <linux/jump_label.h>
+#include <linux/memblock.h>
+#include <linux/psci.h>
+#include <asm/rsi.h>
+
+DEFINE_STATIC_KEY_FALSE_RO(rsi_present);
+EXPORT_SYMBOL(rsi_present);
+
+static bool rsi_version_matches(void)
+{
+	unsigned long ver_lower, ver_higher;
+	unsigned long ret = rsi_request_version(RSI_ABI_VERSION,
+						&ver_lower,
+						&ver_higher);
+
+	if (ret == SMCCC_RET_NOT_SUPPORTED)
+		return false;
+
+	if (ret != RSI_SUCCESS) {
+		pr_err("RME: RMM doesn't support RSI version %lu.%lu. Supported range: %lu.%lu-%lu.%lu\n",
+		       RSI_ABI_VERSION_MAJOR, RSI_ABI_VERSION_MINOR,
+		       RSI_ABI_VERSION_GET_MAJOR(ver_lower),
+		       RSI_ABI_VERSION_GET_MINOR(ver_lower),
+		       RSI_ABI_VERSION_GET_MAJOR(ver_higher),
+		       RSI_ABI_VERSION_GET_MINOR(ver_higher));
+		return false;
+	}
+
+	pr_info("RME: Using RSI version %lu.%lu\n",
+		RSI_ABI_VERSION_GET_MAJOR(ver_lower),
+		RSI_ABI_VERSION_GET_MINOR(ver_lower));
+
+	return true;
+}
+
+static void __init arm64_rsi_setup_memory(void)
+{
+	u64 i;
+	phys_addr_t start, end;
+
+	/*
+	 * Iterate over the available memory ranges and convert the state to
+	 * protected memory. We should take extra care to ensure that we DO NOT
+	 * permit any "DESTROYED" pages to be converted to "RAM".
+	 *
+	 * panic() is used because if the attempt to switch the memory to
+	 * protected has failed here, then future accesses to the memory are
+	 * simply going to be reflected as a SEA (Synchronous External Abort)
+	 * which we can't handle.  Bailing out early prevents the guest limping
+	 * on and dying later.
+	 */
+	for_each_mem_range(i, &start, &end) {
+		if (rsi_set_memory_range_protected_safe(start, end)) {
+			panic("Failed to set memory range to protected: %pa-%pa",
+			      &start, &end);
+		}
+	}
+}
+
+void __init arm64_rsi_init(void)
+{
+	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_SMC)
+		return;
+	if (!rsi_version_matches())
+		return;
+
+	arm64_rsi_setup_memory();
+
+	static_branch_enable(&rsi_present);
+}
+

arch/arm64/kernel/setup.c

@@ -43,6 +43,7 @@
 #include <asm/cpu_ops.h>
 #include <asm/kasan.h>
 #include <asm/numa.h>
+#include <asm/rsi.h>
 #include <asm/scs.h>
 #include <asm/sections.h>
 #include <asm/setup.h>
@@ -351,6 +352,8 @@ void __init __no_sanitize_address setup_arch(char **cmdline_p)
 	else
 		psci_acpi_init();
 
+	arm64_rsi_init();
+
 	init_bootcpu_ops();
 	smp_init_cpus();
 	smp_build_mpidr_hash();