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[175.34.8.244]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-86154048df2sm5208107b3a.61.2026.09.07.23.46.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 07 Sep 2026 23:47:05 -0700 (PDT) Message-ID: <25894d08-0fec-4dcd-9d5e-e8270ff9d26c@redhat.com> Date: Tue, 8 Sep 2026 16:46:52 +1000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v17 2/7] firmware: arm_rmm: Check for RMI support at init To: Suzuki K Poulose , kvm@vger.kernel.org, kvmarm@lists.linux.dev Cc: maz@kernel.org, will@kernel.org, catalin.marinas@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, steven.price@arm.com, aneesh.kumar@kernel.org, oupton@kernel.org, joey.gouly@arm.com, tabba@google.com, yuzenghui@huawei.com, linux-coco@lists.linux.dev, gankulkarni@os.amperecomputing.com, sdonthineni@nvidia.com, alpergun@google.com, fj0570is@fujitsu.com, WeiLin.Chang@arm.com, lpieralisi@kernel.org, enju.kohei@fujitsu.com References: <20260907095942.1140734-1-suzuki.poulose@arm.com> <20260907095942.1140734-3-suzuki.poulose@arm.com> Content-Language: en-US From: Gavin Shan In-Reply-To: <20260907095942.1140734-3-suzuki.poulose@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Suzuki, On 9/7/26 7:59 PM, Suzuki K Poulose wrote: > From: Steven Price > > Query the RMI version number and check if it is a compatible version. > The first two feature registers are read and exposed for future code to > use. > > Signed-off-by: Steven Price > Signed-off-by: Suzuki K Poulose > --- > v17: > * Rename ARM_RMM to ARM_RMM_RMI to make it easier to add Guest facing RSI > support, which is also in progress > v16: > * Update Kconfig text to include PCIe TDISP. > * Export rmi_feat_reg() here rather than in a later commit. > v15: > * The code is moved again, this time into the 'firmware' directory. > v14: > * This moves the basic RMI setup into the 'kernel' directory. This is > because RMI will be used for some features outside of KVM so should > be available even if KVM isn't compiled in. > --- > arch/arm64/Kconfig | 1 + > arch/arm64/kernel/cpufeature.c | 1 + > drivers/firmware/Kconfig | 1 + > drivers/firmware/Makefile | 1 + > drivers/firmware/arm_rmm/Kconfig | 26 ++++++++ > drivers/firmware/arm_rmm/Makefile | 2 + > drivers/firmware/arm_rmm/rmi.c | 101 ++++++++++++++++++++++++++++++ > include/linux/arm-rmi-cmds.h | 34 ++++++++++ > 8 files changed, 167 insertions(+) > create mode 100644 drivers/firmware/arm_rmm/Kconfig > create mode 100644 drivers/firmware/arm_rmm/Makefile > create mode 100644 drivers/firmware/arm_rmm/rmi.c > create mode 100644 include/linux/arm-rmi-cmds.h > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index b5a51b0ef9440..ff9565d3ffa59 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -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 > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index 17b83a2518a8f..db26f6b0eaf5e 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -293,6 +293,7 @@ static const struct arm64_ftr_bits ftr_id_aa64isar3[] = { > static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = { > ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL1_CSV3_SHIFT, 4, 0), > ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL1_CSV2_SHIFT, 4, 0), > + ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL1_RME_SHIFT, 4, 0), > ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL1_DIT_SHIFT, 4, 0), > ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL1_AMU_SHIFT, 4, 0), > ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL1_MPAM_SHIFT, 4, 0), > diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig > index b7cc11e4fbfa6..62660bf520a8d 100644 > --- a/drivers/firmware/Kconfig > +++ b/drivers/firmware/Kconfig > @@ -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 > diff --git a/drivers/firmware/Makefile b/drivers/firmware/Makefile > index be46f1e1dc77f..196a650ccf025 100644 > --- a/drivers/firmware/Makefile > +++ b/drivers/firmware/Makefile > @@ -39,3 +39,4 @@ obj-y += samsung/ > obj-y += smccc/ > obj-y += tegra/ > obj-y += xilinx/ > +obj-y += arm_rmm/ > diff --git a/drivers/firmware/arm_rmm/Kconfig b/drivers/firmware/arm_rmm/Kconfig > new file mode 100644 > index 0000000000000..82724ee23186d > --- /dev/null > +++ b/drivers/firmware/arm_rmm/Kconfig > @@ -0,0 +1,26 @@ > + > +config ARCH_SUPPORTS_RMM > + bool > + > +config ARM_RMM_RMI > + bool "Realm Management Interface (RMI) Support" > + depends on ARCH_SUPPORTS_RMM > + default y > + help > + Support the Realm Management Monitor (RMM) on Arm systems that > + implement the Realm Management Extension (RME), as defined by the > + Arm Confidential Compute Architecture. > + > + The RMM runs at EL2 in the Realm world and provides the Realm > + Management Interface (RMI) used by a Normal World host to create, > + manage and run protected virtual machines called Realms. The RMM can > + also act as a TSM, as defined by the PCIe TDISP and can manage the > + PCI IDE setup for securing the PCIe links. > + > + This option builds the host-side RMI support used by KVM to detect a > + compatible RMM, configure it, manage delegated memory and enable > + Realm guests. > + > + Selecting this option does not by itself make Realm guests available: > + the system must also provide RME-capable hardware and firmware with a > + compatible RMM implementation. > diff --git a/drivers/firmware/arm_rmm/Makefile b/drivers/firmware/arm_rmm/Makefile > new file mode 100644 > index 0000000000000..65171988fdcae > --- /dev/null > +++ b/drivers/firmware/arm_rmm/Makefile > @@ -0,0 +1,2 @@ > + > +obj-$(CONFIG_ARM_RMM_RMI) = rmi.o > diff --git a/drivers/firmware/arm_rmm/rmi.c b/drivers/firmware/arm_rmm/rmi.c > new file mode 100644 > index 0000000000000..008a783407b4e > --- /dev/null > +++ b/drivers/firmware/arm_rmm/rmi.c > @@ -0,0 +1,101 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * Copyright (C) 2023-2026 ARM Ltd. > + */ > + > +#include > +#include > +#include > +#include > + > +#include > +#include > + > +/* Currently only the first 2 registers are used by Linux */ > +#define RMI_FEAT_REG_COUNT 2 > +static __ro_after_init unsigned long rmi_feat_reg_cache[RMI_FEAT_REG_COUNT]; > + I would drop RMI_FEAT_REG_COUNT and use ARRAY_SIZE(rmi_feat_reg_cache) in the code. Besides, __ro_after_init is usually put at the last the declaration. static unsigned long rmi_feat_reg_cache[RMI_FEAT_REG_COUNT] __ro_after_init; > +unsigned long rmi_feat_reg(unsigned long id) > +{ > + if (WARN_ON(id >= RMI_FEAT_REG_COUNT)) > + return 0; > + > + return rmi_feat_reg_cache[id]; > +} > +EXPORT_SYMBOL_GPL(rmi_feat_reg); > + I would suggest to rename 'id' to 'index' since it represents the feature register index instead of feature register ID. unsigned long rmi_feat_reg(unsigned long index) { : } EXPORT_SYMBOL_GPL(rmi_feat_reg); > +static int rmi_check_version(void) > +{ > + struct arm_smccc_res res; > + unsigned short version_major, version_minor; > + unsigned long host_version = RMI_ABI_VERSION(RMI_ABI_MAJOR_VERSION, > + RMI_ABI_MINOR_VERSION); > + unsigned long aa64pfr0 = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1); > + > + /* If RME isn't supported, then RMI can't be */ > + if (cpuid_feature_extract_unsigned_field(aa64pfr0, ID_AA64PFR0_EL1_RME_SHIFT) == 0) > + return -ENXIO; > + > + arm_smccc_1_1_invoke(SMC_RMI_VERSION, host_version, &res); > + > + if (res.a0 == SMCCC_RET_NOT_SUPPORTED) > + return -ENXIO; > + > + version_major = RMI_ABI_VERSION_GET_MAJOR(res.a1); > + version_minor = RMI_ABI_VERSION_GET_MINOR(res.a1); > + > + if (res.a0 != RMI_SUCCESS) { > + unsigned short high_version_major, high_version_minor; > + > + high_version_major = RMI_ABI_VERSION_GET_MAJOR(res.a2); > + high_version_minor = RMI_ABI_VERSION_GET_MINOR(res.a2); > + > + pr_err("Unsupported RMI ABI (v%d.%d - v%d.%d) we want v%d.%d\n", > + version_major, version_minor, > + high_version_major, high_version_minor, > + RMI_ABI_MAJOR_VERSION, > + RMI_ABI_MINOR_VERSION); > + return -ENXIO; > + } > + > + pr_info("RMI ABI version %d.%d\n", version_major, version_minor); > + > + return 0; > +} > + > +static int rmi_read_features(void) > +{ > + /* > + * Since we've negotiated a compatible version these feature registers > + * should always be available > + */ > + for (int i = 0; i < RMI_FEAT_REG_COUNT; i++) { > + if (WARN_ON(rmi_features(i, &rmi_feat_reg_cache[i]))) > + return -EINVAL; > + } > + > + return 0; > +} > + > +static int __init arm64_init_rmi(void) > +{ > + int ret; > + > + /* Continue without realm support if we can't agree on a version */ > + ret = rmi_check_version(); > + if (ret) > + return ret; > + > + ret = rmi_read_features(); > + if (ret) > + return ret; > + > + return 0; > +} > + > +/* > + * Note arm64_init_rmi() must be called before kvm_init_rmi() otherwise KVM > + * will not support realm guests. subsys_initcall() is called before > + * module_init() (used for KVM) so this is OK. > + */ > +subsys_initcall(arm64_init_rmi); > diff --git a/include/linux/arm-rmi-cmds.h b/include/linux/arm-rmi-cmds.h > new file mode 100644 > index 0000000000000..2fb1f7f86d71e > --- /dev/null > +++ b/include/linux/arm-rmi-cmds.h > @@ -0,0 +1,34 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * Copyright (C) 2026 ARM Ltd. > + */ > + > +#ifndef __LINUX_ARM_RMI_CMDS_H_ > +#define __LINUX_ARM_RMI_CMDS_H_ > + > +#include > +#include > +#include > + > +unsigned long rmi_feat_reg(unsigned long id); > + > +/** > + * rmi_features() - Read feature register > + * @index: Feature register index > + * @out: Feature register value is written to this pointer > + * > + * Return: RMI return code > + */ > +static inline int rmi_features(unsigned long index, unsigned long *out) > +{ > + struct arm_smccc_res res; > + > + arm_smccc_1_1_invoke(SMC_RMI_FEATURES, index, &res); > + > + if (res.a0 == RMI_SUCCESS && out) > + *out = res.a1; > + > + return res.a0; > +} > + We needn't expose rmi_features() through include/linux/arm-rmi-cmds.h since it's used for once in rmi.c::rmi_read_features(). I would suggest to drop it by combining the code with that function. > +#endif #endif /* __LINUX_ARM_RMI_CMDS_H_ */ Thanks, Gavin