[RFC PATCH v7 01/13] arm64: realm: Add RHI helper to query IPA state change alignment

["Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org>]

Arm CCA guests can run with a PAGE_SIZE that is smaller than the granule
size used by the host to track Realm IPA state. In that configuration,
changing a guest PAGE_SIZE range between protected and shared state can
cover only part of the host-owned state-change unit.

The Realm Host Interface specification (Arm DEN0148) [1] defines the
Host Configuration interface for querying host capabilities, including
the IPA state change alignment.

Add the RHI HostConf definitions and a get_ipa_state_change_alignment()
helper. The helper uses RSI_HOST_CALL to query the supported HostConf
version and features, and reads the IPA state change alignment when
available. It falls back to PAGE_SIZE if the interface is unavailable or
returns an invalid value.

[1] https://support.arm.com/documentation/den0148/latest/

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 MAINTAINERS                    |  1 +
 drivers/firmware/arm_rmm/rsi.c | 47 ++++++++++++++++++++++++++++++++++
 include/linux/arm-rsi-cmds.h   | 10 ++++++++
 include/linux/arm-smccc-rhi.h  | 25 ++++++++++++++++++
 include/linux/arm-smccc-rsi.h  |  7 +++++
 5 files changed, 90 insertions(+)
 create mode 100644 include/linux/arm-smccc-rhi.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 1e543163a8cc..87ec876868eb 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3956,6 +3956,7 @@ F:	drivers/firmware/arm_rmm/
 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-rhi.h
 F:	include/linux/arm-smccc-rsi.h
 F:	tools/testing/selftests/arm64/
 X:	arch/arm64/boot/dts/
diff --git a/drivers/firmware/arm_rmm/rsi.c b/drivers/firmware/arm_rmm/rsi.c
index 0fcc4e33bd92..883f6091ff95 100644
--- a/drivers/firmware/arm_rmm/rsi.c
+++ b/drivers/firmware/arm_rmm/rsi.c
@@ -8,7 +8,9 @@
 #include <linux/psci.h>
 #include <linux/swiotlb.h>
 #include <linux/arm-rsi-cmds.h>
+#include <linux/arm-smccc-rhi.h>
 #include <linux/kobject.h>
+#include <linux/string.h>
 #include <linux/sysfs.h>
 
 #include <asm/io.h>
@@ -162,6 +164,51 @@ static int realm_register_memory_enc_ops(void)
 	return arm64_mem_crypt_ops_register(&realm_crypt_ops);
 }
 
+/* we need an aligned struct for rsi_host_call. slab is not yet ready */
+static struct rsi_host_call hostconf_call __initdata;
+static unsigned long __maybe_unused __init get_ipa_state_change_alignment(void)
+{
+	long ret;
+	unsigned long shared_granule_size;
+
+	memset(&hostconf_call, 0, sizeof(hostconf_call));
+	hostconf_call.gprs[0] = RHI_HOSTCONF_VERSION;
+	ret = rsi_host_call(lm_alias(&hostconf_call));
+	if (ret != RSI_SUCCESS)
+		goto err_out;
+
+	if (hostconf_call.gprs[0] != RHI_HOSTCONF_VER_1_0)
+		goto err_out;
+
+	memset(&hostconf_call, 0, sizeof(hostconf_call));
+	hostconf_call.gprs[0] = RHI_HOSTCONF_FEATURES;
+	ret = rsi_host_call(lm_alias(&hostconf_call));
+	if (ret != RSI_SUCCESS)
+		goto err_out;
+
+	if (!(hostconf_call.gprs[0] & RHI_HOSTCONF_FEATURE_GET_IPA_CHANGE_ALIGNMENT))
+		goto err_out;
+
+	memset(&hostconf_call, 0, sizeof(hostconf_call));
+	hostconf_call.gprs[0] = RHI_HOSTCONF_GET_IPA_CHANGE_ALIGNMENT;
+	ret = rsi_host_call(lm_alias(&hostconf_call));
+	if (ret != RSI_SUCCESS)
+		goto err_out;
+
+	shared_granule_size = hostconf_call.gprs[0];
+	if (shared_granule_size & (SZ_4K - 1) ||
+	    !is_power_of_2(shared_granule_size))
+		goto err_out;
+
+	return max(PAGE_SIZE, shared_granule_size);
+err_out:
+	/*
+	 * For failure condition assume host is built with 4K page size
+	 * and hence IPA state change alignment can be guest PAGE_SIZE.
+	 */
+	return PAGE_SIZE;
+}
+
 void __init arm64_rsi_init(void)
 {
 	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_SMC)
diff --git a/include/linux/arm-rsi-cmds.h b/include/linux/arm-rsi-cmds.h
index 3f7a6a833993..996f1621b996 100644
--- a/include/linux/arm-rsi-cmds.h
+++ b/include/linux/arm-rsi-cmds.h
@@ -236,4 +236,14 @@ static inline unsigned long rsi_attestation_token_continue(phys_addr_t granule,
 	return res.a0;
 }
 
+static inline unsigned long rsi_host_call(struct rsi_host_call *rhi_call)
+{
+	phys_addr_t addr = virt_to_phys(rhi_call);
+	struct arm_smccc_res res;
+
+	arm_smccc_1_1_invoke(SMC_RSI_HOST_CALL, addr, &res);
+
+	return res.a0;
+}
+
 #endif /* __LINUX_ARM_RSI_CMDS_H_ */
diff --git a/include/linux/arm-smccc-rhi.h b/include/linux/arm-smccc-rhi.h
new file mode 100644
index 000000000000..be89185cddae
--- /dev/null
+++ b/include/linux/arm-smccc-rhi.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2026 ARM Ltd.
+ */
+
+#ifndef __LINUX_ARM_SMCCC_RHI_H_
+#define __LINUX_ARM_SMCCC_RHI_H_
+
+#include <linux/arm-smccc.h>
+
+#define SMC_RHI_CALL(func)				\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,		\
+			   ARM_SMCCC_SMC_64,		\
+			   ARM_SMCCC_OWNER_STANDARD_HYP,\
+			   (func))
+
+#define RHI_HOSTCONF_VER_1_0		0x10000
+#define RHI_HOSTCONF_VERSION		SMC_RHI_CALL(0x004E)
+
+#define RHI_HOSTCONF_FEATURE_GET_IPA_CHANGE_ALIGNMENT	BIT(0)
+#define RHI_HOSTCONF_FEATURES		SMC_RHI_CALL(0x004F)
+
+#define RHI_HOSTCONF_GET_IPA_CHANGE_ALIGNMENT	SMC_RHI_CALL(0x0050)
+
+#endif /* __LINUX_ARM_SMCCC_RHI_H_ */
diff --git a/include/linux/arm-smccc-rsi.h b/include/linux/arm-smccc-rsi.h
index fddb77986f70..3532a3f08f4e 100644
--- a/include/linux/arm-smccc-rsi.h
+++ b/include/linux/arm-smccc-rsi.h
@@ -182,6 +182,13 @@ struct realm_config {
  */
 #define SMC_RSI_IPA_STATE_GET			SMC_RSI_FID(0x198)
 
+struct rsi_host_call {
+	union {
+		u16 imm;
+		u64 padding0;
+	};
+	u64 gprs[31];
+} __aligned(0x100);
 /*
  * Make a Host call.
  *
-- 
2.43.0