[PATCH v3 3/3] coco: guest: arm64: Add Realm Host Interface and hostconf RHI

Aneesh Kumar K.V (Arm)
2026-03-09T10:27:24Z

- describe the Realm Host Interface SMC IDs and result codes in a new
asm/rhi.h header
- expose struct rsi_host_call plus an rsi_host_call() helper so we can
invoke SMC_RSI_HOST_CALL from C code
- add RHI hostconf SMC IDs and helper to query version, features, and IPA
change alignment
- derive the realm hypervisor page size during init and abort realm setup
on invalid alignment

This provides the host page-size discovery needed by previous patch that
align shared buffer allocation/decryption to host requirements.

Cc: Marc Zyngier <maz@kernel.org>
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Steven Price <steven.price@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
arch/arm64/include/asm/mem_encrypt.h | 3 ++
arch/arm64/include/asm/rhi.h | 24 +++++++++++++
arch/arm64/include/asm/rsi.h | 2 ++
arch/arm64/include/asm/rsi_cmds.h | 10 ++++++
arch/arm64/include/asm/rsi_smc.h | 7 ++++
arch/arm64/kernel/Makefile | 2 +-
arch/arm64/kernel/rhi.c | 53 ++++++++++++++++++++++++++++
arch/arm64/kernel/rsi.c | 13 +++++++
arch/arm64/mm/mem_encrypt.c | 8 +++++
9 files changed, 121 insertions(+), 1 deletion(-)
create mode 100644 arch/arm64/include/asm/rhi.h
create mode 100644 arch/arm64/kernel/rhi.c

diff --git a/arch/arm64/include/asm/mem_encrypt.h b/arch/arm64/include/asm/mem_encrypt.h
index 314b2b52025f..5541911eb028 100644
--- a/arch/arm64/include/asm/mem_encrypt.h
+++ b/arch/arm64/include/asm/mem_encrypt.h
@@ -16,6 +16,9 @@ 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);

+#define mem_decrypt_granule_size mem_decrypt_granule_size
+size_t mem_decrypt_granule_size(void);
+
int realm_register_memory_enc_ops(void);

static inline bool force_dma_unencrypted(struct device *dev)
diff --git a/arch/arm64/include/asm/rhi.h b/arch/arm64/include/asm/rhi.h
new file mode 100644
index 000000000000..0895dd92ea1d
--- /dev/null
+++ b/arch/arm64/include/asm/rhi.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2026 ARM Ltd.
+ */
+
+#ifndef __ASM_RHI_H_
+#define __ASM_RHI_H_
+
+#include <linux/types.h>
+
+#define SMC_RHI_CALL(func) \
+ ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \
+ ARM_SMCCC_SMC_64, \
+ ARM_SMCCC_OWNER_STANDARD_HYP,\
+ (func))
+
+unsigned long rhi_get_ipa_change_alignment(void);
+#define RHI_HOSTCONF_VER_1_0 0x10000
+#define RHI_HOSTCONF_VERSION SMC_RHI_CALL(0x004E)
+
+#define __RHI_HOSTCONF_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
diff --git a/arch/arm64/include/asm/rsi.h b/arch/arm64/include/asm/rsi.h
index 88b50d660e85..ae54fb3b1429 100644
--- a/arch/arm64/include/asm/rsi.h
+++ b/arch/arm64/include/asm/rsi.h
@@ -67,4 +67,6 @@ static inline int rsi_set_memory_range_shared(phys_addr_t start,
return rsi_set_memory_range(start, end, RSI_RIPAS_EMPTY,
RSI_CHANGE_DESTROYED);
}
+
+unsigned long realm_get_hyp_pagesize(void);
#endif /* __ASM_RSI_H_ */
diff --git a/arch/arm64/include/asm/rsi_cmds.h b/arch/arm64/include/asm/rsi_cmds.h
index 2c8763876dfb..a341ce0eeda1 100644
--- a/arch/arm64/include/asm/rsi_cmds.h
+++ b/arch/arm64/include/asm/rsi_cmds.h
@@ -159,4 +159,14 @@ 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 /* __ASM_RSI_CMDS_H */
diff --git a/arch/arm64/include/asm/rsi_smc.h b/arch/arm64/include/asm/rsi_smc.h
index e19253f96c94..9ee8b5c7612e 100644
--- a/arch/arm64/include/asm/rsi_smc.h
+++ b/arch/arm64/include/asm/rsi_smc.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.
*
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 76f32e424065..fcb67f50ea89 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -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
+ rsi.o jump_label.o rhi.o

obj-$(CONFIG_COMPAT) += sys32.o signal32.o \
sys_compat.o
diff --git a/arch/arm64/kernel/rhi.c b/arch/arm64/kernel/rhi.c
new file mode 100644
index 000000000000..d2141b5283e1
--- /dev/null
+++ b/arch/arm64/kernel/rhi.c
@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2026 ARM Ltd.
+ */
+
+#include <asm/rsi.h>
+#include <asm/rhi.h>
+
+/* we need an aligned rhicall for rsi_host_call. slab is not yet ready */
+static struct rsi_host_call hyp_pagesize_rhicall;
+unsigned long rhi_get_ipa_change_alignment(void)
+{
+ long ret;
+ unsigned long ipa_change_align;
+
+ hyp_pagesize_rhicall.imm = 0;
+ hyp_pagesize_rhicall.gprs[0] = RHI_HOSTCONF_VERSION;
+ ret = rsi_host_call(&hyp_pagesize_rhicall);
+ if (ret != RSI_SUCCESS)
+ goto err_out;
+
+ if (hyp_pagesize_rhicall.gprs[0] != RHI_HOSTCONF_VER_1_0)
+ goto err_out;
+
+ hyp_pagesize_rhicall.imm = 0;
+ hyp_pagesize_rhicall.gprs[0] = RHI_HOSTCONF_FEATURES;
+ ret = rsi_host_call(&hyp_pagesize_rhicall);
+ if (ret != RSI_SUCCESS)
+ goto err_out;
+
+ if (!(hyp_pagesize_rhicall.gprs[0] & __RHI_HOSTCONF_GET_IPA_CHANGE_ALIGNMENT))
+ goto err_out;
+
+ hyp_pagesize_rhicall.imm = 0;
+ hyp_pagesize_rhicall.gprs[0] = RHI_HOSTCONF_GET_IPA_CHANGE_ALIGNMENT;
+ ret = rsi_host_call(&hyp_pagesize_rhicall);
+ if (ret != RSI_SUCCESS)
+ goto err_out;
+
+ ipa_change_align = hyp_pagesize_rhicall.gprs[0];
+ /* This error needs special handling in the caller */
+ if (ipa_change_align & (SZ_4K - 1))
+ return 0;
+
+ return ipa_change_align;
+
+err_out:
+ /*
+ * For failure condition assume host is built with 4K page size
+ * and hence ipa change alignment can be guest PAGE_SIZE.
+ */
+ return PAGE_SIZE;
+}
diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
index c64a06f58c0b..6e35cb947745 100644
--- a/arch/arm64/kernel/rsi.c
+++ b/arch/arm64/kernel/rsi.c
@@ -13,8 +13,10 @@
#include <asm/io.h>
#include <asm/mem_encrypt.h>
#include <asm/rsi.h>
+#include <asm/rhi.h>

static struct realm_config config;
+static unsigned long ipa_change_alignment = PAGE_SIZE;

unsigned long prot_ns_shared;
EXPORT_SYMBOL(prot_ns_shared);
@@ -138,6 +140,11 @@ static int realm_ioremap_hook(phys_addr_t phys, size_t size, pgprot_t *prot)
return 0;
}

+unsigned long realm_get_hyp_pagesize(void)
+{
+ return ipa_change_alignment;
+}
+
void __init arm64_rsi_init(void)
{
if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_SMC)
@@ -146,6 +153,12 @@ void __init arm64_rsi_init(void)
return;
if (WARN_ON(rsi_get_realm_config(&config)))
return;
+
+ ipa_change_alignment = rhi_get_ipa_change_alignment();
+ /* If we don't get a correct alignment response, don't enable realm */
+ if (!ipa_change_alignment)
+ return;
+
prot_ns_shared = BIT(config.ipa_bits - 1);

if (arm64_ioremap_prot_hook_register(realm_ioremap_hook))
diff --git a/arch/arm64/mm/mem_encrypt.c b/arch/arm64/mm/mem_encrypt.c
index 38c62c9e4e74..f5d64bc29c20 100644
--- a/arch/arm64/mm/mem_encrypt.c
+++ b/arch/arm64/mm/mem_encrypt.c
@@ -59,3 +59,11 @@ int set_memory_decrypted(unsigned long addr, int numpages)
return crypt_ops->decrypt(addr, numpages);
}
EXPORT_SYMBOL_GPL(set_memory_decrypted);
+
+size_t mem_decrypt_granule_size(void)
+{
+ if (is_realm_world())
+ return max(PAGE_SIZE, realm_get_hyp_pagesize());
+ return PAGE_SIZE;
+}
+EXPORT_SYMBOL_GPL(mem_decrypt_granule_size);
--
2.43.0