Re: [PATCH v10 05/43] arm64: RME: Check for RME support at KVM init

[Gavin Shan <gshan@redhat.com>]

On 8/21/25 12:55 AM, Steven Price wrote:
> Query the RMI version number and check if it is a compatible version. A
> static key is also provided to signal that a supported RMM is available.
> 
> Functions are provided to query if a VM or VCPU is a realm (or rec)
> which currently will always return false.
> 
> Later patches make use of struct realm and the states as the ioctls
> interfaces are added to support realm and REC creation and destruction.
> 
> Reviewed-by: Gavin Shan <gshan@redhat.com>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> Changes since v8:
>   * No need to guard kvm_init_rme() behind 'in_hyp_mode'.
> Changes since v6:
>   * Improved message for an unsupported RMI ABI version.
> Changes since v5:
>   * Reword "unsupported" message from "host supports" to "we want" to
>     clarify that 'we' are the 'host'.
> Changes since v2:
>   * Drop return value from kvm_init_rme(), it was always 0.
>   * Rely on the RMM return value to identify whether the RSI ABI is
>     compatible.
> ---
>   arch/arm64/include/asm/kvm_emulate.h | 18 +++++++++
>   arch/arm64/include/asm/kvm_host.h    |  4 ++
>   arch/arm64/include/asm/kvm_rme.h     | 56 ++++++++++++++++++++++++++++
>   arch/arm64/include/asm/virt.h        |  1 +
>   arch/arm64/kvm/Makefile              |  2 +-
>   arch/arm64/kvm/arm.c                 |  5 +++
>   arch/arm64/kvm/rme.c                 | 56 ++++++++++++++++++++++++++++
>   7 files changed, 141 insertions(+), 1 deletion(-)
>   create mode 100644 arch/arm64/include/asm/kvm_rme.h
>   create mode 100644 arch/arm64/kvm/rme.c
> 

[...]

> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 888f7c7abf54..76177c56f1ef 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -40,6 +40,7 @@
>   #include <asm/kvm_nested.h>
>   #include <asm/kvm_pkvm.h>
>   #include <asm/kvm_ptrauth.h>
> +#include <asm/kvm_rme.h>
>   #include <asm/sections.h>
>   

Nit: The header file <asm/kvm_rme.h> has been included to <asm/kvm_host.h> and
<linux/kvm_host.h>, which has been included to arm.c. So this explicit inclusion
can be dropped.

>   #include <kvm/arm_hypercalls.h>
> @@ -59,6 +60,8 @@ enum kvm_wfx_trap_policy {
>   static enum kvm_wfx_trap_policy kvm_wfi_trap_policy __read_mostly = KVM_WFX_NOTRAP_SINGLE_TASK;
>   static enum kvm_wfx_trap_policy kvm_wfe_trap_policy __read_mostly = KVM_WFX_NOTRAP_SINGLE_TASK;
>   
> +DEFINE_STATIC_KEY_FALSE(kvm_rme_is_available);
> +
>   DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
>   
>   DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_base);
> @@ -2836,6 +2839,8 @@ static __init int kvm_arm_init(void)
>   
>   	in_hyp_mode = is_kernel_in_hyp_mode();
>   
> +	kvm_init_rme();
> +
>   	if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) ||
>   	    cpus_have_final_cap(ARM64_WORKAROUND_1508412))
>   		kvm_info("Guests without required CPU erratum workarounds can deadlock system!\n" \
> diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
> new file mode 100644
> index 000000000000..67cf2d94cb2d
> --- /dev/null
> +++ b/arch/arm64/kvm/rme.c
> @@ -0,0 +1,56 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2023 ARM Ltd.
> + */
> +
> +#include <linux/kvm_host.h>
> +
> +#include <asm/rmi_cmds.h>
> +#include <asm/virt.h>
> +
> +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);
> +
> +	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);
> +
> +		kvm_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;
> +	}
> +
> +	kvm_info("RMI ABI version %d.%d\n", version_major, version_minor);
> +
> +	return 0;
> +}
> +
> +void kvm_init_rme(void)
> +{
> +	if (PAGE_SIZE != SZ_4K)
> +		/* Only 4k page size on the host is supported */
> +		return;

Nit: The comment can be moved before the check, something like below. Otherwise,
{} is needed here.

	/* Only 4kB page size is supported */
	if (PAGE_SIZE != SZ_4K)
		return;

> +
> +	if (rmi_check_version())
> +		/* Continue without realm support */
> +		return;

Nit: same as above.

> +
> +	/* Future patch will enable static branch kvm_rme_is_available */
> +}

Thanks,
Gavin