Switch Arm SMCCC firmware services to an SMCCC bus

As discussed here:
https://lore.kernel.org/all/[email protected]

The earlier CCA guest support used an arm-cca-dev platform device as a pure software anchor for the TSM class device. That platform device did not correspond to a DT/ACPI described device, MMIO range, interrupt, or other platform resource; it existed only to make the CCA guest driver bind and to place the resulting TSM device in the driver model. The same pattern also exists for smccc_trng. Creating separate platform devices for such SMCCC-discovered features is misleading, because those features are not independent platform devices.

This series adds an Arm SMCCC bus for services discovered through the SMCCC firmware interface. The bus provides SMCCC device and driver registration helpers, SMCCC function id based matching, uevent modalias generation, and a sysfs modalias attribute. SMCCC service drivers can use MODULE_DEVICE_TABLE(arm_smccc, ...) to emit arm_smccc:f<functionid> aliases, allowing userspace to autoload service drivers when the SMCCC core registers matching firmware-service devices.

The series then moves SMCCC TRNG and the Arm CCA guest RSI service off the platform bus. When the SMCCC core discovers the corresponding firmware service, it registers an arm-smccc device for that service. The hwrng arm_smccc_trng driver and the Arm CCA guest TSM provider are converted to SMCCC drivers that bind to those discovered devices.

The old arm-cca-dev platform device has also been used by userspace as a Realm guest indicator. Removing it without a replacement would leave userspace depending on an internal driver-binding device. This series therefore adds /sys/firmware/cca/realm_guest as a stable, architecture-provided ABI for detecting whether the kernel is running as an Arm CCA Realm guest, and then removes the dummy arm-cca-dev platform-device registration.

Changes from v11:
https://lore.kernel.org/all/[email protected]
* Collect Reviewed-by tags.
* Update commit messages based on feedback.
* Update the sysfs file documentation.
* Use put_device() consistently for cleanup on error.

Changes from v10:
https://lore.kernel.org/all/[email protected]
* Collect Reviewed-by tags.
* Add the missing linux/types.h include.
* Update the arm_smccc_1_1_invoke() call to pass 0 as the input value for x1-x7.

Changes from v9:
https://lore.kernel.org/all/[email protected]
* Rename CONFIG_ARM_RMM to CONFIG_ARM_RMM_RSI to make the Kconfig option RSI-specific.
* Update the modalias to use the SMCCC function ID.
* Don't issue SMC64 SMCCC calls on arm32.
* Drop the IDA usage.

Changes from v8:
https://lore.kernel.org/all/[email protected]
* Rebase onto the arm64 for-next/core branch.
* Move the RSI code from arch/arm64 to drivers/firmware/arm_rmm in patch 3.
* Add a new patch to move the Realm memory-encryption operations to the RSI code.
* Drop the Reviewed-by tag from patch 3.

Changes from v7:
https://lore.kernel.org/all/[email protected]
* Rebase to latest kernel
* Add id_table check in arm_smccc_driver_register
* Add smccc device name check in arm_smccc_device_register
* Drop driver_data from struct arm_smccc_device_id

Changes from v6:
https://lore.kernel.org/all/[email protected]
* Move SMCCC bus-related code to bus.c.
* Remove CONFIG_ARM64 #ifdefs and switch device creation to use the generic function-ID support framework.
* Move version-specific checks and other conditionals to the device driver probe routines.
* Move RSI definitions to include/linux/arm-smccc-rsi.h.
* Split the file and variable renames into a separate patch.

Changes from v5:
https://lore.kernel.org/all/[email protected]
* Replace the arm-smccc platform-device plus auxiliary-child model with a dedicated Arm SMCCC bus.
* Add SMCCC module alias support so SMCCC service drivers can use MODULE_DEVICE_TABLE(arm_smccc, ...) and autoload through arm_smccc:<name> aliases.
* Convert smccc_trng from a platform driver to an SMCCC driver.
* Convert the Arm CCA guest TSM provider from the arm-cca-dev platform device to an SMCCC driver bound to the discovered RSI service.
* Add /sys/firmware/cca/realm_guest before removing the old arm-cca-dev dummy platform device.

Changes from v4:
https://lore.kernel.org/all/[email protected]
* Add /sys/firmware/cca/realm_guest for detecting realm guest
* Convert smccc_trng to auxiliary device from platform device

Changes from v3:
https://lore.kernel.org/all/[email protected]
* Rebased onto the latest kernel
* Drop pr_fmt() from drivers/firmware/smccc/rmm.c

Aneesh Kumar K.V (Arm) (7):
firmware: smccc: Add an Arm SMCCC bus
firmware: hwrng: arm_smccc_trng: Register as an SMCCC device
firmware: arm_rmm: Move RSI support out of arch/arm64
arm64: realm: Move Realm memory encryption ops to RSI code
virt: coco: arm-cca-guest: Rename TSM report source file
firmware: smccc: arm-cca-guest: Bind the TSM provider to an SMCCC
device
coco: guest: arm64: Replace dummy CCA device with sysfs ABI

 Documentation/ABI/testing/sysfs-firmware-cca  |   7 +
 MAINTAINERS                                   |   3 +
 arch/arm/include/asm/archrandom.h             |   2 +-
 arch/arm64/Kconfig                            |   1 +
 arch/arm64/include/asm/archrandom.h           |   2 +-
 arch/arm64/include/asm/io.h                   |   2 +-
 arch/arm64/include/asm/mem_encrypt.h          |   5 +-
 arch/arm64/include/asm/pgtable-prot.h         |   2 +-
 arch/arm64/include/asm/rsi.h                  |  70 --------
 arch/arm64/kernel/Makefile                    |   2 +-
 arch/arm64/kernel/setup.c                     |   2 +-
 arch/arm64/mm/init.c                          |   3 +-
 arch/arm64/mm/pageattr.c                      |  38 +----
 drivers/char/hw_random/arm_smccc_trng.c       |  32 ++--
 drivers/firmware/Kconfig                      |   1 +
 drivers/firmware/Makefile                     |   1 +
 drivers/firmware/arm_rmm/Kconfig              |  17 ++
 drivers/firmware/arm_rmm/Makefile             |   2 +
 .../kernel => drivers/firmware/arm_rmm}/rsi.c |  79 +++++++--
 drivers/firmware/smccc/Makefile               |   2 +-
 drivers/firmware/smccc/bus.c                  | 158 ++++++++++++++++++
 drivers/firmware/smccc/smccc.c                |  68 +++++++-
 drivers/virt/coco/arm-cca-guest/Kconfig       |   3 +-
 drivers/virt/coco/arm-cca-guest/Makefile      |   2 +
 .../arm-cca-guest/{arm-cca-guest.c => main.c} |  52 +++---
 .../linux/arm-rsi-cmds.h                      |  76 ++++++++-
 include/linux/arm-smccc-bus.h                 |  48 ++++++
 .../linux/arm-smccc-rsi.h                     |   6 +-
 include/linux/device-id/arm_smccc.h           |  19 +++
 include/linux/mod_devicetable.h               |   1 +
 scripts/mod/devicetable-offsets.c             |   3 +
 scripts/mod/file2alias.c                      |   8 +
 32 files changed, 528 insertions(+), 189 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-firmware-cca
 delete mode 100644 arch/arm64/include/asm/rsi.h
 create mode 100644 drivers/firmware/arm_rmm/Kconfig
 create mode 100644 drivers/firmware/arm_rmm/Makefile
 rename {arch/arm64/kernel => drivers/firmware/arm_rmm}/rsi.c (71%)
 create mode 100644 drivers/firmware/smccc/bus.c
 rename drivers/virt/coco/arm-cca-guest/{arm-cca-guest.c => main.c} (82%)
 rename arch/arm64/include/asm/rsi_cmds.h => include/linux/arm-rsi-cmds.h (69%)
 create mode 100644 include/linux/arm-smccc-bus.h
 rename arch/arm64/include/asm/rsi_smc.h => include/linux/arm-smccc-rsi.h (98%)
 create mode 100644 include/linux/device-id/arm_smccc.h

base-commit: 704340f1cd0dcef829eb62f5b48ae95a2ce17bdf

2.43.0

SMCCC-discovered firmware services are currently represented by separate platform devices, such as smccc_trng and arm-cca-dev. Those devices do not represent independent DT/ACPI-described platform resources; they are features of the SMCCC firmware interface.

Add an Arm SMCCC bus for services discovered through the SMCCC firmware interface. The bus provides SMCCC device and driver registration helpers, function ID based matching, modalias generation, and a sysfs modalias attribute so SMCCC service drivers can bind to discovered firmware services and autoload as modules.

Follow-up changes can then register SMCCC firmware services as arm-smccc devices instead of creating independent per-feature platform devices.

Based on arm_ffa code

---
 MAINTAINERS                         |   1 +
 drivers/firmware/smccc/Makefile     |   2 +-
 drivers/firmware/smccc/bus.c        | 158 ++++++++++++++++++++++++++++
 include/linux/arm-smccc-bus.h       |  48 +++++++++
 include/linux/device-id/arm_smccc.h |  19 ++++
 include/linux/mod_devicetable.h     |   1 +
 scripts/mod/devicetable-offsets.c   |   3 +
 scripts/mod/file2alias.c            |   8 ++
 8 files changed, 239 insertions(+), 1 deletion(-)
 create mode 100644 drivers/firmware/smccc/bus.c
 create mode 100644 include/linux/arm-smccc-bus.h
 create mode 100644 include/linux/device-id/arm_smccc.h

index c2414447892c..42364c540f50 100644
@@ -24741,6 +24741,7 @@ M:	Sudeep Holla <[email protected]>
 L:	[email protected] (moderated for non-subscribers)
 S:	Maintained
 F:	drivers/firmware/smccc/
+F:	include/linux/arm-smccc-bus.h
 F:	include/linux/arm-smccc.h
 
 SECURITY CONTACT

index 40d19144a860..68bbff1407b8 100644
@@ -1,4 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0
 #
-obj-$(CONFIG_HAVE_ARM_SMCCC_DISCOVERY)	+= smccc.o kvm_guest.o
+obj-$(CONFIG_HAVE_ARM_SMCCC_DISCOVERY)	+= bus.o smccc.o kvm_guest.o
 obj-$(CONFIG_ARM_SMCCC_SOC_ID)	+= soc_id.o

new file mode 100644
index 000000000000..a8579832fc1c
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_DEVICE_ID_ARM_SMCCC_H
+#define __LINUX_DEVICE_ID_ARM_SMCCC_H
+
+#ifdef __KERNEL__
+#include <linux/types.h>
+#endif
+
+#define ARM_SMCCC_MODULE_PREFIX "arm_smccc:"
+
+/**
+ * struct arm_smccc_device_id - Arm SMCCC bus device identifier
+ * @func_id: SMCCC function identifier
+ */
+struct arm_smccc_device_id {
+	__u32 func_id;
+};
+
+#endif /* __LINUX_DEVICE_ID_ARM_SMCCC_H */

index a397213bedac..318c4b5c3451 100644
@@ -16,6 +16,7 @@
 #include "device-id/amba.h"
 #include "device-id/ap.h"
 #include "device-id/apr.h"
+#include "device-id/arm_smccc.h"
 #include "device-id/auxiliary.h"
 #include "device-id/bcma.h"
 #include "device-id/ccw.h"

index b4178c42d08f..1492e9fdc7cb 100644
@@ -254,6 +254,9 @@ int main(void)
 	DEVID(auxiliary_device_id);
 	DEVID_FIELD(auxiliary_device_id, name);
 
+	DEVID(arm_smccc_device_id);
+	DEVID_FIELD(arm_smccc_device_id, func_id);
+
 	DEVID(ssam_device_id);
 	DEVID_FIELD(ssam_device_id, match_flags);
 	DEVID_FIELD(ssam_device_id, domain);

index 8d36c74dec2d..980d7da456bb 100644
@@ -1349,6 +1349,13 @@ static void do_auxiliary_entry(struct module *mod, void *symval)
 	module_alias_printf(mod, false, AUXILIARY_MODULE_PREFIX "%s", *name);
 }
 
+static void do_arm_smccc_entry(struct module *mod, void *symval)
+{
+	DEF_FIELD(symval, arm_smccc_device_id, func_id);
+
+	module_alias_printf(mod, false, ARM_SMCCC_MODULE_PREFIX "f%08X", func_id);
+}
+
 /*
  * Looks like: ssam:dNcNtNiNfN
  *

@@ -1519,6 +1526,7 @@ static const struct devtable devtable[] = {
 	{"mhi", SIZE_mhi_device_id, do_mhi_entry},
 	{"mhi_ep", SIZE_mhi_device_id, do_mhi_ep_entry},
 	{"auxiliary", SIZE_auxiliary_device_id, do_auxiliary_entry},
+	{"arm_smccc", SIZE_arm_smccc_device_id, do_arm_smccc_entry},
 	{"ssam", SIZE_ssam_device_id, do_ssam_entry},
 	{"dfl", SIZE_dfl_device_id, do_dfl_entry},
 	{"ishtp", SIZE_ishtp_device_id, do_ishtp_entry},

2.43.0

I didn't add it because I couldn't find any other device-id files tracked in MAINTAINERS.

-aneesh

The SMCCC TRNG interface is a firmware-provided SMCCC service rather than a standalone platform device. Now that the SMCCC core has an SMCCC bus, create an arm-smccc-trng device for the discovered TRNG service and convert the hwrng driver to an SMCCC driver.

The SMCCC id table preserves module autoloading for systems where the TRNG driver is built as a module.

The sysfs device path changes from the old smccc_trng platform-device path to an arm-smccc device path. No known userspace dependency on the old path was found; a Debian Code Search lookup for the existing platform-device name/path did not find any users.

---
 arch/arm/include/asm/archrandom.h       |  2 +-
 arch/arm64/include/asm/archrandom.h     |  2 +-
 drivers/char/hw_random/arm_smccc_trng.c | 32 ++++++++-----
 drivers/firmware/smccc/smccc.c          | 62 +++++++++++++++++++++----
 4 files changed, 76 insertions(+), 22 deletions(-)

index cc4714eb1a75..ee39a03ddf8a 100644
@@ -2,7 +2,7 @@
 #ifndef _ASM_ARCHRANDOM_H
 #define _ASM_ARCHRANDOM_H
 
-static inline bool __init smccc_probe_trng(void)
+static inline bool smccc_probe_trng(void)
 {
 	return false;
 }

index 8babfbe31f95..7605dd81bd1e 100644
@@ -12,7 +12,7 @@
 
 extern bool smccc_trng_available;
 
-static inline bool __init smccc_probe_trng(void)
+static inline bool smccc_probe_trng(void)
 {
 	struct arm_smccc_res res;
 

index dcb8e7f37f25..01c1a30cbab8 100644
@@ -16,8 +16,10 @@
 #include <linux/device.h>
 #include <linux/hw_random.h>
 #include <linux/module.h>
-#include <linux/platform_device.h>
 #include <linux/arm-smccc.h>
+#include <linux/arm-smccc-bus.h>
+
+#include <asm/archrandom.h>
 
 #ifdef CONFIG_ARM64
 #define ARM_SMCCC_TRNG_RND	ARM_SMCCC_TRNG_RND64

@@ -94,29 +96,37 @@ static int smccc_trng_read(struct hwrng *rng, void *data, size_t max, bool wait)
 	return copied;
 }
 
-static int smccc_trng_probe(struct platform_device *pdev)
+static int smccc_trng_probe(struct arm_smccc_device *sdev)
 {
 	struct hwrng *trng;
 
-	trng = devm_kzalloc(&pdev->dev, sizeof(*trng), GFP_KERNEL);
+	/* validate the minimum version requirement */
+	if (!smccc_probe_trng())
+		return -ENODEV;
+
+	trng = devm_kzalloc(&sdev->dev, sizeof(*trng), GFP_KERNEL);
 	if (!trng)
 		return -ENOMEM;
 
 	trng->name = "smccc_trng";
 	trng->read = smccc_trng_read;
 
-	return devm_hwrng_register(&pdev->dev, trng);
+	return devm_hwrng_register(&sdev->dev, trng);
 }
 
-static struct platform_driver smccc_trng_driver = {
-	.driver = {
-		.name		= "smccc_trng",
-	},
-	.probe		= smccc_trng_probe,
+static const struct arm_smccc_device_id smccc_trng_id_table[] = {
+	{ .func_id = ARM_SMCCC_TRNG_VERSION },
+	{}
+};
+MODULE_DEVICE_TABLE(arm_smccc, smccc_trng_id_table);
+
+static struct arm_smccc_driver smccc_trng_driver = {
+	.name	  = KBUILD_MODNAME,
+	.probe	  = smccc_trng_probe,
+	.id_table = smccc_trng_id_table,
 };
-module_platform_driver(smccc_trng_driver);
+module_arm_smccc_driver(smccc_trng_driver);
 
-MODULE_ALIAS("platform:smccc_trng");
 MODULE_AUTHOR("Andre Przywara");
 MODULE_DESCRIPTION("Arm SMCCC TRNG firmware interface support");
 MODULE_LICENSE("GPL");

2.43.0

I asked you two times already to cc the hw_random maintainers. Not adding them again but not merging this stuff without their ack either. So, up to you.

Catalin

Sorry, I missed that. I'll repost and Cc the hw_random maintainers.

-aneesh

The RSI SMCCC function IDs describe a firmware ABI and are not arm64 architecture specific definitions. Follow-up changes need to use them from non-arch code, including drivers/firmware/smccc and the Arm CCA guest driver.

Move the complete Realm Service Interface (RSI) implementation from arch/arm64 to drivers/firmware/arm_rmm. The RSI SMCCC definitions and command helpers are also moved to include/linux so they can be shared by architecture code and firmware or driver code. This also keeps the firmware interface outside architecture code, as requested [1].

[1] https://lore.kernel.org/all/agsNO9cc7H-b0H8L@willie-the-truck

---
 MAINTAINERS                                   |  2 +
 arch/arm64/Kconfig                            |  1 +
 arch/arm64/include/asm/io.h                   |  2 +-
 arch/arm64/include/asm/mem_encrypt.h          |  2 +-
 arch/arm64/include/asm/pgtable-prot.h         |  2 +-
 arch/arm64/include/asm/rsi.h                  | 70 -----------------
 arch/arm64/kernel/Makefile                    |  2 +-
 arch/arm64/kernel/setup.c                     |  2 +-
 arch/arm64/mm/init.c                          |  3 +-
 drivers/firmware/Kconfig                      |  1 +
 drivers/firmware/Makefile                     |  1 +
 drivers/firmware/arm_rmm/Kconfig              | 17 ++++
 drivers/firmware/arm_rmm/Makefile             |  2 +
 .../kernel => drivers/firmware/arm_rmm}/rsi.c |  2 +-
 drivers/virt/coco/arm-cca-guest/Kconfig       |  2 +-
 .../virt/coco/arm-cca-guest/arm-cca-guest.c   |  5 +-
 .../linux/arm-rsi-cmds.h                      | 77 +++++++++++++++++--
 .../linux/arm-smccc-rsi.h                     |  6 +-
 18 files changed, 110 insertions(+), 89 deletions(-)
 delete mode 100644 arch/arm64/include/asm/rsi.h
 create mode 100644 drivers/firmware/arm_rmm/Kconfig
 create mode 100644 drivers/firmware/arm_rmm/Makefile
 rename {arch/arm64/kernel => drivers/firmware/arm_rmm}/rsi.c (99%)
 rename arch/arm64/include/asm/rsi_cmds.h => include/linux/arm-rsi-cmds.h (69%)
 rename arch/arm64/include/asm/rsi_smc.h => include/linux/arm-smccc-rsi.h (98%)

index 42364c540f50..b867d537a579 100644
@@ -3953,6 +3953,8 @@ F:	Documentation/arch/arm64/
 F:	arch/arm64/
 F:	drivers/virt/coco/arm-cca-guest/
 F:	drivers/virt/coco/pkvm-guest/
+F:	include/linux/arm-rsi-cmds.h
+F:	include/linux/arm-smccc-rsi.h
 F:	tools/testing/selftests/arm64/
 X:	arch/arm64/boot/dts/
 X:	arch/arm64/configs/defconfig

index b5a51b0ef944..ff9565d3ffa5 100644
@@ -38,6 +38,7 @@ config ARM64
 	select ARCH_HAS_MEMBARRIER_SYNC_CORE
 	select ARCH_HAS_MEM_ENCRYPT
 	select ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS
+	select ARCH_SUPPORTS_RMM
 	select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
 	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
 	select ARCH_HAS_NONLEAF_PMD_YOUNG if ARM64_HAFT

index 49a7002661a9..1620537f0332 100644
@@ -8,6 +8,7 @@
 #ifndef __ASM_IO_H
 #define __ASM_IO_H
 
+#include <linux/arm-rsi-cmds.h>
 #include <linux/types.h>
 #include <linux/pgtable.h>
 

@@ -17,7 +18,6 @@
 #include <asm/early_ioremap.h>
 #include <asm/alternative.h>
 #include <asm/cpufeature.h>
-#include <asm/rsi.h>
 
 /*
  * Generic IO read/write.  These perform native-endian accesses.

index 636f45b4d8af..f03b9d7b83b4 100644
@@ -2,8 +2,8 @@
 #ifndef __ASM_MEM_ENCRYPT_H
 #define __ASM_MEM_ENCRYPT_H
 
+#include <linux/arm-rsi-cmds.h>
 #include <asm/hypervisor.h>
-#include <asm/rsi.h>
 
 struct device;
 

index 09d7c00cf405..58e71e592175 100644
@@ -66,9 +66,9 @@
 
 #ifndef __ASSEMBLER__
 
+#include <linux/arm-rsi-cmds.h>
 #include <asm/cpufeature.h>
 #include <asm/pgtable-types.h>
-#include <asm/rsi.h>
 
 extern bool arm64_use_ng_mappings;
 extern unsigned long prot_ns_shared;

index d2690c3ec528..21fc3a3d25c9 100644
@@ -34,7 +34,7 @@ obj-y			:= debug-monitors.o entry.o irq.o fpsimd.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/	\
-			   rsi.o jump_label.o
+			   jump_label.o
 
 obj-$(CONFIG_COMPAT)			+= sys32.o signal32.o			\
 					   sys_compat.o

index 29c6100f0c50..a707deba6ae7 100644
@@ -7,6 +7,7 @@
  */
 
 #include <linux/acpi.h>
+#include <linux/arm-rsi-cmds.h>
 #include <linux/export.h>
 #include <linux/kernel.h>
 #include <linux/stddef.h>

@@ -43,7 +44,6 @@
 #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>

index fbf215ecc7d0..2a8de20d2b44 100644
@@ -34,6 +34,8 @@
 #include <linux/acpi_iort.h>
 #include <linux/kmemleak.h>
 #include <linux/execmem.h>
+#include <linux/arm-rsi-cmds.h>
+
 
 #include <asm/boot.h>
 #include <asm/fixmap.h>

@@ -43,7 +45,6 @@
 #include <asm/kvm_host.h>
 #include <asm/memory.h>
 #include <asm/numa.h>
-#include <asm/rsi.h>
 #include <asm/sections.h>
 #include <asm/setup.h>
 #include <linux/sizes.h>

index b7cc11e4fbfa..62660bf520a8 100644
@@ -310,5 +310,6 @@ source "drivers/firmware/samsung/Kconfig"
 source "drivers/firmware/smccc/Kconfig"
 source "drivers/firmware/tegra/Kconfig"
 source "drivers/firmware/xilinx/Kconfig"
+source "drivers/firmware/arm_rmm/Kconfig"
 
 endmenu

index be46f1e1dc77..196a650ccf02 100644
@@ -39,3 +39,4 @@ obj-y				+= samsung/
 obj-y				+= smccc/
 obj-y				+= tegra/
 obj-y				+= xilinx/
+obj-y				+= arm_rmm/

new file mode 100644
index 000000000000..e981e12fdbe6
@@ -0,0 +1,17 @@
+
+config ARCH_SUPPORTS_RMM
+	bool
+
+config ARM_RMM_RSI
+	bool "Realm Service Interface (RSI) Support"
+	depends on ARCH_SUPPORTS_RMM
+	default y
+	help
+	  Enable support for running Linux as a Realm guest under a Realm
+	  Management Monitor (RMM), as defined by the Arm Confidential
+	  Compute Architecture.
+
+	  The RMM exposes the Realm Service Interface (RSI) to Realm guests.
+	  Linux uses RSI to negotiate the interface version, obtain the Realm
+	  configuration, and manage the protected or shared state of guest
+	  memory.

new file mode 100644
index 000000000000..3708b37a9aaf
@@ -0,0 +1,2 @@
+
+obj-$(CONFIG_ARM_RMM_RSI)	= rsi.o

similarity index 99%
rename from arch/arm64/kernel/rsi.c
rename to drivers/firmware/arm_rmm/rsi.c
index 25ca75ce1a4d..8e716f1c1e31 100644
@@ -8,11 +8,11 @@
 #include <linux/psci.h>
 #include <linux/swiotlb.h>
 #include <linux/platform_device.h>
+#include <linux/arm-rsi-cmds.h>
 
 #include <asm/io.h>
 #include <asm/mem_encrypt.h>
 #include <asm/pgtable.h>
-#include <asm/rsi.h>
 
 static struct realm_config config;
 

index 3f0f013f03f1..2582ebb36922 100644
@@ -1,6 +1,6 @@
 config ARM_CCA_GUEST
 	tristate "Arm CCA Guest driver"
-	depends on ARM64
+	depends on ARM_RMM_RSI
 	select TSM_REPORTS
 	help
 	  The driver provides userspace interface to request and

index 0eeddd1ff05b..b741643d1364 100644
@@ -3,7 +3,8 @@
  * Copyright (C) 2023 ARM Ltd.
  */
 
-#include <linux/arm-smccc.h>
+#include <linux/arm-rsi-cmds.h>
+#include <linux/arm-smccc-rsi.h>
 #include <linux/cc_platform.h>
 #include <linux/kernel.h>
 #include <linux/device-id/platform.h>

@@ -12,8 +13,6 @@
 #include <linux/tsm.h>
 #include <linux/types.h>
 
-#include <asm/rsi.h>
-
 /**
  * struct arm_cca_token_info - a descriptor for the token buffer.
  * @granule:		PA of the granule to which the token will be written

similarity index 98%
rename from arch/arm64/include/asm/rsi_smc.h
rename to include/linux/arm-smccc-rsi.h
index e19253f96c94..fddb77986f70 100644
@@ -3,8 +3,8 @@
  * Copyright (C) 2023 ARM Ltd.
  */
 
-#ifndef __ASM_RSI_SMC_H_
-#define __ASM_RSI_SMC_H_
+#ifndef __LINUX_ARM_SMCCC_RSI_H_
+#define __LINUX_ARM_SMCCC_RSI_H_
 
 #include <linux/arm-smccc.h>
 

@@ -190,4 +190,4 @@ struct realm_config {
  */
 #define SMC_RSI_HOST_CALL			SMC_RSI_FID(0x199)
 
-#endif /* __ASM_RSI_SMC_H_ */
+#endif /* __LINUX_ARM_SMCCC_RSI_H_ */

2.43.0

Realm memory encryption callbacks are CCA-specific. Keep the Realm callback registration with the RSI initialization code instead of pageattr.c, which only needs to provide the low-level page-attribute transition helper.

Export __set_memory_enc_dec() within arm64 so the RSI code can wrap it with the Realm-specific encrypt/decrypt callbacks and warning policy.

No functional changes in this patch.

---
 arch/arm64/include/asm/mem_encrypt.h |  3 +--
 arch/arm64/mm/pageattr.c             | 38 +---------------------------
 drivers/firmware/arm_rmm/rsi.c       | 34 +++++++++++++++++++++++++
 3 files changed, 36 insertions(+), 39 deletions(-)

index f03b9d7b83b4..ef8b8463e52b 100644
@@ -16,8 +16,7 @@ int arm64_mem_crypt_ops_register(const struct arm64_mem_crypt_ops *ops);
 
 int set_memory_encrypted(unsigned long addr, int numpages);
 int set_memory_decrypted(unsigned long addr, int numpages);
-
-int realm_register_memory_enc_ops(void);
+int __set_memory_enc_dec(unsigned long addr, int numpages, bool encrypt);
 
 static inline bool force_dma_unencrypted(struct device *dev)
 {

index bbe98ac9ad8c..14b2a3801f40 100644
@@ -275,9 +275,7 @@ int set_direct_map_default_noflush(struct page *page)
 				 PAGE_SIZE, set_mask, clear_mask);
 }
 
-static int __set_memory_enc_dec(unsigned long addr,
-				int numpages,
-				bool encrypt)
+int __set_memory_enc_dec(unsigned long addr, int numpages, bool encrypt)
 {
 	unsigned long set_prot = 0, clear_prot = 0;
 	phys_addr_t start, end;

@@ -321,40 +319,6 @@ static int __set_memory_enc_dec(unsigned long addr,
 				      __pgprot(PTE_PRESENT_INVALID));
 }
 
-static int realm_set_memory_encrypted(unsigned long addr, int numpages)
-{
-	int ret = __set_memory_enc_dec(addr, numpages, true);
-
-	/*
-	 * If the request to change state fails, then the only sensible cause
-	 * of action for the caller is to leak the memory
-	 */
-	WARN(ret, "Failed to encrypt memory, %d pages will be leaked",
-	     numpages);
-
-	return ret;
-}
-
-static int realm_set_memory_decrypted(unsigned long addr, int numpages)
-{
-	int ret = __set_memory_enc_dec(addr, numpages, false);
-
-	WARN(ret, "Failed to decrypt memory, %d pages will be leaked",
-	     numpages);
-
-	return ret;
-}
-
-static const struct arm64_mem_crypt_ops realm_crypt_ops = {
-	.encrypt = realm_set_memory_encrypted,
-	.decrypt = realm_set_memory_decrypted,
-};
-
-int realm_register_memory_enc_ops(void)
-{
-	return arm64_mem_crypt_ops_register(&realm_crypt_ops);
-}
-
 int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)
 {
 	unsigned long addr = (unsigned long)page_address(page);

index 8e716f1c1e31..ada139d0e344 100644
@@ -127,6 +127,40 @@ static int realm_ioremap_hook(phys_addr_t phys, size_t size, pgprot_t *prot)
 	return 0;
 }
 
+static int realm_set_memory_encrypted(unsigned long addr, int numpages)
+{
+	int ret = __set_memory_enc_dec(addr, numpages, true);
+
+	/*
+	 * If the request to change state fails, then the only sensible cause
+	 * of action for the caller is to leak the memory
+	 */
+	WARN(ret, "Failed to encrypt memory, %d pages will be leaked",
+	     numpages);
+
+	return ret;
+}
+
+static int realm_set_memory_decrypted(unsigned long addr, int numpages)
+{
+	int ret = __set_memory_enc_dec(addr, numpages, false);
+
+	WARN(ret, "Failed to decrypt memory, %d pages will be leaked",
+	     numpages);
+
+	return ret;
+}
+
+static const struct arm64_mem_crypt_ops realm_crypt_ops = {
+	.encrypt = realm_set_memory_encrypted,
+	.decrypt = realm_set_memory_decrypted,
+};
+
+static int realm_register_memory_enc_ops(void)
+{
+	return arm64_mem_crypt_ops_register(&realm_crypt_ops);
+}
+
 void __init arm64_rsi_init(void)
 {
 	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_SMC)

2.43.0

Nit: Suzuki's still at arm ;)

Catalin

Will fix. I copied it from:

https://lore.kernel.org/all/[email protected]

-aneesh

;-)

Yikes, my bad.

for FWIW, I really meant :

Mostly for completeness and so I don't read it in a possible v13.

The Arm CCA guest driver currently only implements TSM report support, but follow-up changes will add more TSM-related functionality to the same module.

Rename arm-cca-guest.c to main.c and build it as an object of the arm-cca-guest module. This leaves room for the module to grow additional source files.

Also rename the arm_cca_tsm_ops instance to arm_cca_tsm_report_ops to distinguish the report operations from other TSM functionality that will be added.

---
 drivers/virt/coco/arm-cca-guest/Makefile                    | 2 ++
 drivers/virt/coco/arm-cca-guest/{arm-cca-guest.c => main.c} | 6 +++---
 2 files changed, 5 insertions(+), 3 deletions(-)
 rename drivers/virt/coco/arm-cca-guest/{arm-cca-guest.c => main.c} (97%)

index 69eeba08e98a..7564f4fcc4a4 100644
@@ -1,2 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_ARM_CCA_GUEST) += arm-cca-guest.o
+
+arm-cca-guest-y += main.o

similarity index 97%
rename from drivers/virt/coco/arm-cca-guest/arm-cca-guest.c
rename to drivers/virt/coco/arm-cca-guest/main.c
index b741643d1364..80659f0885e9 100644
@@ -156,7 +156,7 @@ static int arm_cca_report_new(struct tsm_report *report, void *data)
 	return ret;
 }
 
-static const struct tsm_report_ops arm_cca_tsm_ops = {
+static const struct tsm_report_ops arm_cca_tsm_report_ops = {
 	.name = KBUILD_MODNAME,
 	.report_new = arm_cca_report_new,
 };

@@ -177,7 +177,7 @@ static int __init arm_cca_guest_init(void)
 	if (!is_realm_world())
 		return -ENODEV;
 
-	ret = tsm_report_register(&arm_cca_tsm_ops, NULL);
+	ret = tsm_report_register(&arm_cca_tsm_report_ops, NULL);
 	if (ret < 0)
 		pr_err("Error %d registering with TSM\n", ret);
 

@@ -191,7 +191,7 @@ module_init(arm_cca_guest_init);
  */
 static void __exit arm_cca_guest_exit(void)
 {
-	tsm_report_unregister(&arm_cca_tsm_ops);
+	tsm_report_unregister(&arm_cca_tsm_report_ops);
 }
 module_exit(arm_cca_guest_exit);
 

2.43.0

The Arm CCA guest TSM provider currently binds through the arm-cca-dev platform device. Like arm-smccc-trng, this device is not an independent platform resource; it is a software representation of the RSI firmware service discovered through SMCCC.

Move RSI discovery into the SMCCC firmware driver. When the SMCCC conduit is SMC and if RSI ABI version call is supported, create an arm-rsi SMCCC device. Convert the Arm CCA guest TSM provider to an SMCCC driver so it binds to that discovered RSI service and keeps module autoloading through the SMCCC device id table.

Keep the old arm-cca-dev platform-device registration for now. Userspace has used that device as a Realm-guest indicator, so removing it is left to a follow-up patch that adds a replacement sysfs ABI.

---
 drivers/firmware/arm_rmm/rsi.c          |  2 +-
 drivers/firmware/smccc/smccc.c          |  6 ++++
 drivers/virt/coco/arm-cca-guest/Kconfig |  1 +
 drivers/virt/coco/arm-cca-guest/main.c  | 41 ++++++++++---------------
 include/linux/arm-rsi-cmds.h            |  1 -
 5 files changed, 25 insertions(+), 26 deletions(-)

index ada139d0e344..2dd69febedbd 100644
@@ -183,7 +183,7 @@ void __init arm64_rsi_init(void)
 }
 
 static struct platform_device rsi_dev = {
-	.name = RSI_PDEV_NAME,
+	.name = "arm-cca-dev",
 	.id = PLATFORM_DEVID_NONE
 };
 

index 67e503dac409..afc2e4d602ba 100644
@@ -10,6 +10,7 @@
 #include <linux/arm-smccc.h>
 #include <linux/kernel.h>
 #include <linux/arm-smccc-bus.h>
+#include <linux/arm-smccc-rsi.h>
 
 #include <asm/archrandom.h>
 

@@ -94,6 +95,11 @@ static const struct smccc_device_info smccc_devices[] __initconst = {
 		.requires_smc   = false,
 		.device_name    = "arm-smccc-trng",
 	},
+	{
+		.func_id        = SMC_RSI_ABI_VERSION,
+		.requires_smc   = true,
+		.device_name    = "arm-rsi",
+	},
 };
 
 static bool __init smccc_probe_smccc_device(const struct smccc_device_info *smccc_dev)

index 2582ebb36922..0d4ce72e2d86 100644
@@ -1,6 +1,7 @@
 config ARM_CCA_GUEST
 	tristate "Arm CCA Guest driver"
 	depends on ARM_RMM_RSI
+	depends on HAVE_ARM_SMCCC_DISCOVERY
 	select TSM_REPORTS
 	help
 	  The driver provides userspace interface to request and

index 9e8a8c189ca1..3f7a6a833993 100644
@@ -11,7 +11,6 @@
 #include <linux/string.h>
 #include <asm/memory.h>
 
-#define RSI_PDEV_NAME "arm-cca-dev"
 #ifdef CONFIG_ARM_RMM_RSI
 DECLARE_STATIC_KEY_FALSE(rsi_present);
 

2.43.0

The SMCCC firmware driver now creates the arm_smccc bus and instantiates the CCA RSI device once the RSI ABI is discovered. The arm64-specific arm-cca-dev platform device stub is therefore no longer needed.

However, userspace has used the arm-cca-dev platform device to detect Arm CCA Realm guests [1]. Removing it without a replacement would break that detection and would also leave userspace depending on kernel device-model details.

Add /sys/firmware/cca/realm_guest as a stable ABI for detecting whether the kernel is running as an Arm CCA Realm guest. Create the file only in Realm world, where it reads 1.

Remove the dummy arm-cca-dev registration now that userspace has a dedicated CCA Realm guest indicator, and document the new ABI in Documentation/ABI/testing/sysfs-firmware-cca.

---
 Documentation/ABI/testing/sysfs-firmware-cca |  7 ++++
 drivers/firmware/arm_rmm/rsi.c               | 43 +++++++++++++++-----
 2 files changed, 39 insertions(+), 11 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-firmware-cca

new file mode 100644
index 000000000000..9cc355724f94
@@ -0,0 +1,7 @@
+What:		/sys/firmware/cca/realm_guest
+Date:		May 2026
+Contact:	Linux ARM Kernel Mailing list <[email protected]>
+Description:	Read-only. Present only when the kernel is running as an
+		Arm Confidential Compute Architecture (CCA) Realm guest, in
+		which case it reads 1. If the file does not exist, the kernel
+		is not running as a Realm guest.

2.43.0